A Review on Polymer–Quantum Dots Nanocomposite Membrane and Its Multifunctional Applications

Abstract

Polymer–quantum dot (QD) nanocomposite membranes represent a new class of advanced separationmaterials that extend the functionality of conventional polymer membranes beyond passive transport. Incorporating QDs with controlled size, composition, and surface chemistry enables simultaneous enhancement of permeability, selectivity, and stability, while introducing active features such as antifouling, antimicrobial activity, photocatalytic self‐cleaning, and chemical sensing. This review summarizes recent progress in polymer–QD membranes, focusing on how structural design and interfacial engineering dictate multifunctional performance. Major QD categories carbon‐based, semiconductor, and metal oxide are examined with emphasis on dispersion control, compatibility with polymer matrices, and long‐term durability. Applications in water and wastewater treatment, gas separation, and barrier technologies are highlighted, illustrating the shift from inert fillers to reactive, performance‐driving nanocomponents. The review also outlines emerging design principles, fabrication strategies, and pathways toward scalable manufacturing. Key challenges such as consistent QD synthesis, large‐scale membrane production, and operational stability under realistic conditions are critically assessed. Largely, the study provides a unified framework to guide the rational development and practical deployment of polymer‐QD nanocomposite membranes for advanced separation and environmental applications.

Polymer–quantum dots nanocomposite membranes are advanced materials that surpass conventional polymer membranes by integrating enhanced transport with active functionalities. This review highlights design strategies, material interactions, and their applications in water treatment, gas separation, food and biomedical systems.

1. Introduction

Polymeric membranes have become indispensable components in modern separation, purification, sensing, packaging, and biomedical technologies because of their low cost, ease of fabrication, and mechanical flexibility [1]. Over the past several decades, extensive efforts have been devoted to optimizing polymer chemistry, membrane morphology, and processing routes to meet application‐specific demands. Despite these advances, conventional polymer membranes remain fundamentally limited by their passive nature [2]. Their performance is predominantly dictated by intrinsic polymer properties such as free volume, chain packing, and surface chemistry, which restrict their ability to simultaneously achieve high permeability, high selectivity, and long‐term operational stability [3]. The well‐known permeability‐selectivity tradeoff continues to constrain membrane efficiency across applications ranging from water desalination and gas separation to pervaporation and food packaging. Attempts to overcome this tradeoff through polymer blending or chemical modification often leadto marginal improvements and introduce new challenges such as phase incompatibility or loss of mechanical integrity. In addition to transport limitations, fouling represents a persistent and costly problem for polymer membranes. Most commercial polymers lack inherent resistance to organic adsorption, microbial attachment, or biofilm formation [4, 5, 6]. As a result, membrane fouling leads to flux decline, increased energy consumption, frequent chemical cleaning, and reduced service life [7]. Conventional membranes also exhibit limited resistance to harsh operating environments, including oxidative agents, ultraviolet radiation, and aggressive solvents, which can cause polymer degradation, swelling, or plasticization. Perhaps more importantly, traditional polymer membranes are functionally narrow [8, 9, 10]. They are designed to separate, block, or transport species, but they cannot actively interact with their environment, provide feedback, or perform additional tasks such as contaminant degradation or real‐time sensing [11, 12, 13]. As membrane technologies evolve toward more complex and demanding applications, these limitations have become increasingly apparent.

Nanocomposite membranes were introduced as a promising strategy to transcend the constraints of neat polymer systems. By incorporating nanoscale fillers into polymer matrices, researchers have demonstrated improvements in permeability, selectivity, mechanical strength, and fouling resistance. A wide range of nanofillers, including metal oxides, silica, zeolites, graphene‐based materials, and carbon nanotubes, have been explored to tailor membrane structure and surface properties [14]. In particular, metallic nanoparticles such as silver have been extensively incorporated into polymer matrices to impart antibacterial functionality in water treatment and biomedical membranes, primarily through controlled ion release and reactive oxygen species (ROS) generation [15, 16]. Copper and copper oxide nanoparticles have similarly attracted attention due to their antimicrobial efficacy and catalytic activity, while offering cost advantages compared to silver‐based systems [17]. Beyond noble and transition metal nanoparticles, metal oxides such as TiO₂ and ZnO have been integrated to introduce photocatalytic self‐cleaning behavior and enhanced antifouling performance [18, 19]. These fillers can disrupt polymer chain packing, increase free volume, introduce preferential transport pathways, or enhance hydrophilicity, thereby modulating membrane permeability, selectivity, and fouling resistance [20, 21, 22]. While such approaches have yielded notable performance enhancements, most traditional nanocomposite membranes remain fundamentally passive [23]. The fillers primarily serve as structural modifiers, and their role is largely limited to improving existing membrane properties rather than introducing new functionalities. The growing demand for membranes capable of performing multiple tasks simultaneously has highlighted the need for nanofillers that go beyond passive reinforcement. Emerging applications increasingly require membranes that can resist fouling autonomously, respond to external stimuli, degrade pollutants, inhibit microbial growth, or provide real‐time information about operating conditions [24]. Achieving such multifunctionality necessitates the integration of active nanomaterials that can impart new physical, chemical, or biological functions to the membrane system. In this context, quantum dots (QDs) have emerged as particularly attractive candidates for next‐generation polymer nanocomposite (PNC) membranes [25, 26, 27].

QDs are zero‐dimensional (0D) nanomaterials, typically below 10 nm in size, with size‐dependent electronic, optical, and chemical properties [28]. Their ultrasmall dimensions enable intimate interaction with polymer chains, minimizing disruption to membrane integrity while maximizing interfacial effects. Unlike larger nanoparticles, QDs possess a high surface‐to‐volume ratio and abundant surface functional groups, allowing fine control over their dispersion, surface chemistry, and interaction with polymer matrices [29, 30]. This makes them especially suitable for membrane applications, where uniform distribution and interfacial compatibility are critical [31]. One of the most distinctive advantages of QDs over conventional nanofillers is their intrinsic activity. Semiconductor QDs exhibit tunable photoluminescence and photoactivity, enabling membranes to function as optical sensors or photocatalytic platforms [32, 33, 34, 35]. Carbon‐based QDs, including carbon QDs (CQDs) and graphene QDs (GQDs), offer excellent water dispersibility, low toxicity, and rich surface chemistry, making them ideal for enhancing membrane hydrophilicity, antifouling behavior, and antimicrobial performance. Metal oxide QDs further contribute catalytic and redox functionalities that can be exploited for pollutant degradation or self‐cleaning membranes [36]. These active properties are fundamentally different from those of traditional fillers such as silica or alumina, which mainly influence membrane morphology and mechanical properties without contributing dynamic functionality [37, 38, 39]. Another critical distinction lies in the role QDs play at the polymer–filler interface [40]. Passive fillers generally act as inert inclusions, and their performance benefits depend largely on physical effects such as pore formation or polymer chain disruption. In contrast, QDs can actively participate in transport and surface processes [41]. They can modulate surface charge, generate reactive species under light irradiation, facilitate selective interactions with target molecules, or respond to environmental stimuli such as pH and light. As a result, polymer–QDs nanocomposite membranes can achieve multifunctionality within a single material platform, combining separation with sensing, antimicrobial activity, or catalytic behavior [42, 43, 44, 45, 46, 47]. Importantly, the versatility of QDs allows their integration across a wide range of polymer systems and membrane fabrication methods, including phase inversion, interfacial polymerization (IP), surface coating, and electrospinning [17]. This adaptability has led to rapid growth in reported applications, spanning water and wastewater treatment [48, 49, 50, 51], gas separation [52, 53], food packaging [54, 55, 56], biomedical membranes [57, 58, 59], and smart filtration systems. However, the expanding body of literature is highly fragmented, often focusing on specific QD types or isolated applications without establishing broader structure–property–function relationships. Critical issues such as long‐term stability, QD leaching, scalability, and comparative performance against other nanofillers are frequently underexplored or inconsistently reported [26, 60].

The novelty of the present review lies in its integrative and critical perspective on polymer–QD nanocomposite membranes. Rather than treating QDs merely as another class of nanofillers, this review positions them as active functional components that fundamentally transform membrane behavior. By systematically examining how QD chemistry, surface functionality, and interfacial interactions influence membrane structure, transport properties, and multifunctional performance, this article aims to bridge the gap between material design and application‐driven requirements. Emphasis is placed on distinguishing passive property enhancement from true functional activation, comparing QDs with conventional nanofillers, and identifying unresolved challenges that hinder real‐world implementation.

2. Nanocomposite Membranes

Nanocomposite membranes were developed to overcome intrinsic limitations of pristine polymeric membranes by incorporating nanoscale fillers that tailor structure, surface chemistry, and transport behavior. In these systems, nanoparticles dispersed within or on a polymer matrix create synergistic polymer–filler interactions that enhance permeability, selectivity, mechanical stability, and fouling resistance. Owing to their high surface area, nanomaterials can induce significant interfacial effects even at low loadings (Table 1). Nanocomposite membranes are commonly classified according to nanofiller dimensionality. 0D materials, including nanoparticles and QDs, primarily modulate local free volume, surface energy, and interfacial chemistry. One‐dimensional (1D) fillers such as carbon nanotubes and nanofibers that can provide rapid transport pathways and mechanical reinforcement. Two‐dimensional (2D) materials, including graphene oxide (GO) and MXenes, introduce lamellar transport channels and tunable surface charge. Among these, 0D nanoparticles have been most widely explored due to their compatibility with conventional fabrication techniques such as phase inversion, solution casting, and IP. Metal oxide nanoparticles including TiO₂, ZnO, Al₂O₃, and SiO₂ are among the earliest and most studied fillers. They are typically incorporated to enhance hydrophilicity, mechanical strength, and antifouling performance. For example, TiO₂ nanoparticles improve water permeability and can impart photocatalytic self‐cleaning properties under UV irradiation. Similarly, silica nanoparticles have been used to increase membrane porosity and thermal stability [61, 62]. Despite these benefits, conventional inorganic fillers primarily provide passive structural enhancement, and higher loading levels often induce aggregation and nonselective defect formation. Carbon nanotubes offer high aspect ratios and smooth inner channels that facilitate rapid water or gas transport, yet challenges related to dispersion, cost, and polymer–filler compatibility remain significant. GO and related 2D materials introduce oxygen‐containing functional groups that improve hydrophilicity and enable charge‐based separation. Although they have demonstrated enhanced flux and fouling resistance in water treatment and gas separation, their planar geometry can hinder uniform dispersion and promote interfacial void formation. In recent years, QDs have emerged as a distinct and increasingly important class of nanofillers within nanocomposite membranes. Unlike conventional nanoparticles, QDs possess size‐dependent electronic and optical properties, rich surface chemistry, and ultrasmall dimensions. These features allow QDs to integrate more homogeneously within polymer matrices while introducing active functionalities such as photoluminescence, antimicrobial activity, and catalytic behavior. Compared to traditional nanofillers, QDs can simultaneously enhance membrane permeability, antifouling performance, and multifunctionality without significantly compromising mechanical integrity.

TABLE 1.

Typically used nanoparticles in nanocomposite membranes.

Nanoparticle type	Materials	Imposed features into membrane	Advantages	Limitations	References
Metal oxide NPs	TiO2, ZnO, Al2O3, SiO2	Hydrophilicity enhancement, mechanical reinforcement	Low cost, chemical stability, fouling resistance	Passive functionality, aggregation at high loading	[61, 62, 63, 64, 65, 66]
Carbon nanotubes	SWCNTs, MWCNTs	Fast transport pathways, mechanical strength	High permeability, high aspect ratio	Dispersion difficulty, cost, interfacial defects	[67, 68, 69, 70]
Graphene‐based NPs	Graphene oxide, reduced GO	Charge‐based separation, antifouling	High surface area, tunable chemistry	Restacking, nonselective voids	[71, 72, 73, 74]
Clay‐based NPs	Montmorillonite, Halloysite nanotubes, Laponite	Improved mechanical strength, enhanced hydrophilicity, increased ion‐exchange capacity	Abundant, low cost, high aspect ratio, good chemical stability	Potential swelling, dispersion challenges, possible pore blockage	[75, 76, 77]
Metal‐organic NPs	Zeolites, MOFs	Molecular sieving, selectivity enhancement	Well‐defined pores, high selectivity	Interfacial compatibility issues	[8, 61, 78, 79, 80]
QDs	CQDs, GQDs, CdSe QDs	Multifunctionality (sensing, antimicrobial, catalytic)	Ultrasmall size, active behavior, good dispersion	Stability, leaching, scalability concerns	[81, 82, 83, 84, 85]

While metal oxides, carbon nanotubes, and graphene derivatives have demonstrated measurable improvements in permeability and fouling resistance, their performance enhancements are primarily structural in nature arising from modified free volume, altered hydrophilicity, or reinforcement effects. For example, TiO₂ or SiO₂ filled membranes typically improve flux through increased surface wettability but may suffer from nanoparticle aggregation and nonselective void formation at loadings exceeding ∼1–3 wt% [86, 87]. Similarly, carbon nanotubes can provide rapid transport pathways; however, their high aspect ratio and strong van der Waals interactions often complicate homogeneous dispersion and interfacial compatibility [88, 89]. In contrast, QD‐based membranes operate through both structural and physicochemical mechanisms [90]. Due to their ultrasmall size (<10 nm) and high surface area, QDs more effectively modulate local polymer chain packing without creating large interfacial defects. Moreover, quantum confinement effects generate reactive surface states that enable photocatalytic, antimicrobial, or redox‐active functionality under operational conditions [47]. Compared with GO sheets, which may induce planar stacking and interlayer voids, QDs provide isotropic distribution within the polymer matrix, reducing the likelihood of nonselective leakage pathways. Under comparable antifouling testing conditions, QDs incorporated membranes frequently demonstrate higher ROS generation efficiency relative to bulk TiO₂ nanoparticles, particularly in visible light responsive systems [91]. CQDs and GQDs further offer superior aqueous dispersibility and reduced toxicity compared with metal oxide or silver nanoparticles, making them attractive for water treatment and biomedical separation applications [92, 93]. However, QD systems are not without challenges. Their higher surface energy can promote aggregation if surface functionalization is insufficient, and synthesis reproducibility may influence batch‐to‐batch consistency. Therefore, while QDs extend nanocomposite membranes beyond passive enhancement toward multifunctional platforms, systematic benchmarking studies under standardized operational parameters remain essential to quantitatively validate their advantages over established nanofillers.

Nanofiltration (NF) membranes are widely applied for dye and organic pollutant removal from wastewater. A GO/ZIF‐7 nanocomposite layer deposited on a chitosan‐coated PES substrate improved membrane hydrophilicity (contact angle reduced from 84.9° to 64.5°) and enhanced Direct Red 16 rejection (∼94%) compared to the pristine membrane (∼84%), albeit with an 11.4% decline in pure water flux due to added transport resistance [94]. To improve flux–rejection balance and operational stability, thin‐film nanocomposite (TFN) membranes incorporating amine‐rich synthetic talc (NHST) nanosheets within a polydopamine (PDA)‐modified support have been reported [95]. Compared to thin‐film composite (TFC) membranes, NHST‐TFN membranes exhibited increased hydrophilicity and significantly higher water flux. Similarly, incorporation of amine‐functionalized cloisite Na⁺ clay nanosheets (NH₂‐CMMT) resulted in ∼99%  ± 0.5% rejection of DIC and TRI, outperforming conventional TFC membranes under prolonged operation [96]. Carbon nanotube‐based modifications have also been explored. Functionalized MWCNTs (hydroxyl‐ and carboxyl‐modified) improved PVDF membrane hydrophilicity, surface charge, porosity, and antifouling behavior, leading to enhanced dye separation performance [97]. ZnO/PMMA nanocomposite membranes demonstrated improved dielectric properties and optical limiting behavior with increasing nanoparticle loading, while TiO₂‐GO incorporated PES membranes showed superior photocatalytic degradation of methyl orange (68.6%) compared to TiO₂ (48%) or GO (43.5%) alone at identical filler content [18, 98]. Beyond pollutant removal, advanced nanocomposite architectures have been developed for solar‐driven desalination [99]. A double‐layer membrane combining MXene (photothermal absorption) and reduced GO (selective mass transport) achieved enhanced solar absorption and salt rejection. Addressing the permeability‐selectivity tradeoff in polyamide (PA) NF membranes, a capillary‐assisted IP (CAIP) strategy (Figure 1) enabled fabrication of MOF‐PA nanocomposite membranes with improved pore uniformity and reduced surface charge, achieving high water permeance (∼18.7 LMH bar⁻¹) alongside exceptional selectivity between nutrient ions and PFAS.

FIGURE 1.

CAIP‐MOF membrane compared with the traditional TFC (TIP) and TFN (TIP‐MOF and ILIP‐MOF) membranes. (a) Schematic illustrating the capillary rise of water‐phase solution in the nanochannels of the PES membrane (pointed by single‐tailed arrows) and the MOF layer (pointed by double‐tailed arrows). (b) Rejection of inorganic ions. (c) Rejection of representative PFASs. (d) Membrane water permeance and nutrient/PFAS selectivity (SPNI, PFAS). The TIP‐MOF, ILIP‐MOF, and CAIP‐MOF membranes were fabricated under preoptimized conditions. Reproduced from Reference [100]. Copyright (2022), with permission from American Chemical Society.

Seah et al. investigated the influence of organic solvent temperature on TFN membranes incorporating surface‐functionalized GO for NF. Increasing the IP temperature to 55°C enhanced reaction kinetics, producing a more cross‐linked and rougher PA layer [101]. This membrane achieved superior Na₂SO₄ rejection (99%) with a water–salt permselectivity ratio of 11.0 more than twice that of a commercial reference membrane (4.88). However, the increased surface roughness promoted protein adhesion despite the improved hydrophilicity imparted by GO. In contrast, membranes fabricated at 0°C formed a thinner, smoother PA layer, resulting in higher water flux and improved antifouling performance. Stable filtration was maintained over 12 h, with GO nanosheets remaining well embedded within the selective layer. In another study, PVDF‐based nanocomposite membranes incorporating polyaniline (PANI) and titanium nanotubes (TNT) were fabricated via phase inversion (Figure 2) [102]. The addition of PANI‐TNT improved hydrophilicity, leading to a significant increase in pure water flux (484.8 ± 2.9 L m⁻² h⁻¹) compared to pristine PVDF (312.0 ± 1.9 L m⁻² h⁻¹). The membranes also exhibited enhanced dye removal (methyl orange and Allura red) and demonstrated UV‐induced self‐cleaning capability, highlighting the multifunctional advantages of nanocomposite design.

FIGURE 2.

Schematic illustrations of the manufacturing process of nanocomposite membrane. Reproduced from reference [102]. Copyright (2021), with permission from Elsevier.

3. Advantages of QDs: Passive Fillers Versus Active Functional QDs

PNC membranes depend significantly on the selection and functionality of integrated nanofillers, which crucially influence both structural and operational efficacy. Conventional passive fillers, including silica, alumina, titanium dioxide, zeolites, and carbon nanotubes, have been utilized to enhance membrane characteristics by improving hydrophilicity, mechanical strength, thermal stability, and surface roughness. These materials serve largely as inert structural modifiers, affecting polymer chain arrangement, free volume, and pore development without engaging in chemical or optical processes. TiO₂ nanoparticles integrated into polysulfone (PSF) or polyvinylidene fluoride (PVDF) membranes augment water flux by enhancing hydrophilicity and facilitate photocatalytic self‐cleaning under UV light; nevertheless, their principal function is structural, with functional activity generally confined to surface‐mediated processes. Likewise, silica and alumina nanoparticles enhance selectivity and mechanical strength by reinforcing pore walls and establishing preferential transport channels; nevertheless, they lack active sensing, antibacterial, or catalytic functions. Carbon‐based nanomaterials, including GO and carbon nanotubes, can enhance fast transport and antifouling properties but remain predominantly inert unless explicitly functionalized. Generally, passive fillers effectively enhance properties; nevertheless, their ability to facilitate multifunctionality is fundamentally limited, frequently requiring high filler loadings or intricate postmodification procedures.

Conversely, QDs constitute a category of active functional nanofillers that significantly enhance membrane functionalities beyond just passive reinforcement. QDs are 0D nanoparticles, generally measuring less than 10 nm, exhibiting electrical, optical, and chemical capabilities that are contingent upon their size. Their diminutive size facilitates uniform distribution inside polymer matrices with negligible disturbance to membrane integrity, while their extensive surface chemistry promotes robust interfacial interactions and adjustable compatibility with various polymers. CQDs and GQDs improve membrane hydrophilicity and antifouling properties while concurrently providing optical sensing functionalities owing to their inherent photoluminescence. Semiconductor QDs, such as CdSe or ZnS, can facilitate the formation ofROS, offering antibacterial and photocatalytic properties for water purification or self‐cleaning membranes. In contrast to passive fillers, QDs are not confined to structural activities; they engage actively in separation, sensing, and chemical transformations, enabling a single membrane to incorporate many functionalities without sacrificing its permeability or selectivity. Furthermore, functionalized QDs (FQDs) can be customized for precise interactions with target molecules, hence improving selectivity in gas separation, pollutant elimination, or bioactive membranes. The multifunctionality of QDs signifies a paradigm shift in membrane design, wherein active nanomaterials supplant the conventional “property‐only” methodology with function‐oriented engineering. In addition to multifunctionality, QDs provide superior operating performance and scalability compared to passive fillers. Their nanoscale size mitigates the likelihood of aggregation, a prevalent drawback of traditional nanoparticles that might result in nonselective gaps or diminish effective surface area (Figure 3). QDs can be included into many polymer systems and production techniques, including as phase inversion, IP, electrospinning, and layer‐by‐layer assembly. Moreover, QDs provide dynamic reactions to environmental stimuli, such pH, light, or temperature, so enabling membranes to adjust to fluctuating operational conditions, a functionality seldom attainable with passive fillers. The integration of structural reinforcement, active functionality, and responsive behavior renders QDs as adaptable and revolutionary elements in advanced PNC membranes.

FIGURE 3.

Comparison between passive fillers versus active QDs in nanocomposite membranes.

The efficacy of PES membranes was improved through the integration of PMO‐PPD and CQD nanomaterials. The composite membranes exhibited superior hydrophilic characteristics, decreased fouling, augmented antibacterial efficacy, and heightened pollution removal capacities. Characterization techniques validated the successful production and incorporation of the nanoparticles into the membrane matrix [103]. The incorporation of PMO‐PPD/CQDs markedly enhanced pure water flux and fouling resistance relative to pristine PES membranes. The M3 membrane, comprising 0.1 wt% PMO‐PPD and 0.4 wt% CQDs nanofiller, demonstrated superior performance in water flux (81.3 L m⁻² h⁻¹), bovine serum albumin (BSA) rejection (29.5 L m⁻² h⁻¹), foul resistance ratio (63.7%), total resistance (58%), reversible resistance (21.6%), and irreversible resistance (36.3%). M3 exhibited the best pollutant removal efficiencies among the manufactured membranes, achieving 89.76% for Pb(II) at an initial concentration of 30 mg L⁻¹, 93.7% for MO at an initial dosage of 40 mg L⁻¹, and 36.77% for NaCl at an initial concentration of 200 mg L⁻¹. 2D MXene nanosheets have emerged as a promising contender for use as functional fillers in anticorrosion coatings. Nonetheless, the self‐stacking of MXene nanosheets and their high conductivity constrained the long‐term anticorrosion efficacy of the coating [104]. The ZnO QDs decorated MXene hybrid was synthesized through electrostatic assembly, modified with aminosilane using 3‐aminopropyltriethoxysilane (ATPES), and employed as a functional filler to enhance the waterborne epoxy coating (WEP) via a straightforward spraying technique (Figure 4). Boron nitride particles modified with carbon quantum dots (CDs@BNOH) were produced as high thermal conductivity composite fillers and subsequently integrated into a possibly biocompatible silk fibroin hydrogel patch [105]. The CDs@BNOH/SilMA patch has a commendable and steady recyclable thermal conductivity of 0.77 W m^–1 K^–1 reflecting a 15.38% enhancement in overall thermal conductivity attributed to the incorporation of CQDs.

FIGURE 4.

Thermal conduction mechanisms in CDs@BNOH/SilMA. Reproduced from reference [105]. Copyright (2025), with permission from American Chemical Society.

In a separate work, hyperbranched polymers containing many active groups were effectively grafted onto the surface of graphene. A compact cross‐linked network was established within the coating by incorporating three‐dimensional dendritic hyperbranched polymers with 2D graphene. Graphene undergoes noncovalent modification by nitrogen‐doped carbon quantum dot (N‐CQD), while hyperbranched polymers are grafted onto the graphene surface via the active groups of the CQDs, therefore substantially enhancing the density of active sites on the graphene surface. The prepared coating was exposed to a high‐temperature, high‐pressure CO₂ atmosphere and immersed in a 3.5 wt% NaCl solution for 22 days [106]. The low‐frequency impedance modulus of the coating, as determined by electrochemical impedance spectroscopy (EIS), was 1010 Ω·cm², three orders of magnitude greater than that of the unmodified graphene coating, signifying outstanding shielding efficacy under severe conditions. In the Taber abrasion test, the coating demonstrated an average mass loss of merely 24.63 mg/1000 r, indicating exceptional wear resistance and a 50% enhancement in tensile strength relative to the unmodified graphene coating. A separate study detailed the manufacture of fluorescent bio‐based UV‐curable polyurethane acrylate (PUA) and examined the alterations in various specifications of these coatings resulting from the incorporation of CQDs. Castor oil was utilized as a natural and biocompatible alternative to chemical polyols for the synthesis of PUA oligomer [107]. CQDs were produced using the microwave‐assisted pyrolysis of a starch and water mixture. Electroscopic methods were employed to characterize the synthesized coatings and to evaluate the reinforcing effect of CQDs on the resulting nanocomposite. The incorporation of 0.5 wt% CQDs into PUA resin enhanced the adhesion strength and thermal stability of the PUA/CQDs (0.5 wt%) coating in comparison to the pure PUA coating.

4. Types of QDs Used in Membranes

Numerous categories of QDs have been investigated in membrane research, each with unique attributes, benefits, and possible applications. This encompasses CQDs, GQDs, semiconductor QDs such as CdSe, ZnS, and PbS, metal oxide QDs like TiO₂ and ZnO, as well as doped or surface‐FQDs designed for certain capabilities.

CQDs are extensively researched in membrane systems owing to their straightforward manufacturing, low toxicity, excellent aqueous dispersibility, and robust interfacial compatibility with polymers. CQDs generally measure between 2 and 10 nm and have a carbon core adorned with functional groups containing oxygen or nitrogen, facilitating hydrogen bonding, electrostatic interactions, or covalent bonding to polymer matrices. In membrane applications, CQDs have been integrated into various polymer matrices, including PVDF, PSF, PES, chitosan, and polyvinyl alcohol (PVA). The integration of CQDs augments hydrophilicity, elevates water flux, and promotes antifouling and antibacterial characteristics. Furthermore, the inherent photoluminescence of CQDs enables the functionalization of membranes for optical sensing and environmental surveillance. CQD‐embedded membranes have exhibited the capacity to detect heavy metal ions or tiny organic molecules in water while preserving selective permeability, integrating separation and sensing capabilities within a single material.

GQDs represent a category of carbon‐based 0D nanomaterials, characterized by their crystalline graphene domains and oxygenated edge sites. GQDs amalgamate the advantages of graphene, including substantial surface area and superior mechanical strength, with quantum confinement features that provide adjustable photoluminescence and electrical characteristics. Incorporating GQDs into polymer membranes improves structural stability, augments hydrophilicity, and imparts antibacterial properties. Moreover, GQDs enhance charge‐mediated separation processes, rendering them especially effective for the removal of ionic or charged species in water treatment. The 2D graphene fragments in GQDs facilitate efficient electron transport and photocatalytic activity under visible light, resulting in multifunctional membranes that can self‐clean or degrade reactive pollutants. Bi et al. devised a novel methodology for the design and fabrication of NF membranes by pore engineering utilizing GQDs [108]. An in‐situ IP reaction occurred between GQDs and trimesoyl chloride (TMC) within the pores of ultrafiltration (UF) membranes, subsequently followed by thermal treatment. The irreversible contraction of membrane bulk material due to thermal treatment guaranteed the stable retention of the GQDs nanoaggregates. The pore architecture of the resulting membranes was elucidated by scanning electron microscopy (SEM), positron annihilation spectroscopy (PAS), Brunauer–Emmett–Teller (BET) analysis, and neutral solute rejection studies. The voids within GQDs nanoaggregates created the holes of the resultant membranes, with a radius that can be adjusted between 1.21 and 1.72 nm by varying the quantity of GQDs added. The resulting membranes demonstrated an ultrafast water penetration rate of 244.7 [L/(m²  h bar)], approximately 5–6 times greater than previously reported data, with rejection rates for Alcian blue and Congo red reaching 92.9% and 98.8%, respectively. Yang et al. produced polyethyleneimine (PEI) functionalized GQDs as aqueous phase monomers and fabricated an ultrathin desalination membrane by IP. The in situ implanted GQDs, exhibiting exceptionally uniform dispersion, create numerous nanopores in the membrane, while PEI chains occupy the newly formed nanopores, preventing the emergence of excessively large nanopores [109]. Furthermore, the PEI‐grafted GQDs exhibit a reduced diffusion rate during interphase, resulting in an ultrathin selective layer. Leveraging its ultrathin thickness (∼6.5 nm), extensive water routes (specific surface area: 6.73 m²/g), and enlarged pore size (∼0.82 nm), the PA‐NGQD600 membrane demonstrates remarkable pure water permeance (38.5 L m⁻² h⁻¹ bar⁻¹) and inorganic salt rejection (95.5% for Na₂SO₄). Yeh et al. developed a distinctive self‐diagnosis bioresource‐derived nitrogen‐doped GQDs (NGQDs)‐based TFN membrane with regulated optical characteristics and optimized porous nanostructures for exceptional water transport and purification [82]. Their comprehensive experimental and computational investigations indicate that nanoscale NGQDs with numerous surface functional groups can facilitate the development of targeted porous structures during membrane fabrication, resulting in an exceptional water permeability of 289 L m⁻² h⁻¹ bar⁻¹ (LMHB) and impressive 99.96% separation efficiency for various organic dyes. Interlayered‐thin film nanocomposite (i‐TFN) membranes, using nanomaterials as the interlayer, have garnered increasing interest from researchers in recent years due to their effective modulation of the separation layer architecture in membrane separation applications [110]. This study involved the synthesis of amino‐functionalized graphene quantum dots and their application as an interlayer to enhance the PES UF substrate (Figure 5). Subsequently, IP was conducted between TMC and β‐cyclodextrin (β‐CD) to synthesize innovative i‐TFN polyarylate membranes for CO₂/N₂ separation.

FIGURE 5.

Schematic diagram of interlayered‐thin film nanocomposite (i‐TFN) membranes prepared by interfacial polymerization (IP). Reproduced from reference [110]. Copyright (2022), with permission from Elsevier.

Semiconductor QDs, such as CdSe, ZnS, PbS, and associated chalcogenide materials, constitute a category of QDs that have distinctive optical and electrical properties. These QDs demonstrate size‐dependent bandgaps and photoluminescence, rendering them advantageous for sensing and photocatalytic applications in membranes. The integration of semiconductor QDs into polymeric membranes can facilitate photocatalytic self‐cleaning, antibacterial properties, or selective adsorption when exposed to light irradiation. CdSe QDs incorporated in PVDF or PSF matrices have demonstrated the ability to decompose organic contaminants in water and diminish bacterial growth on membrane surfaces. ZnS QDs are employed to augment UV or visible‐light‐induced catalytic activity while preserving structural integrity and water transport efficiency. The potential cytotoxicity of heavy‐metal‐based semiconductor QDs requires meticulous surface functionalization or encapsulation to avert leaching and guarantee safe utilization in water treatment and biomedical applications. CdS QDs were effectively encapsulated in a polysulfone membrane (PSM) to create a photoactive membrane for application in wastewater remediation under solar illumination [111]. The CdS@PSM membranes were fabricated via the nonsolvent induced phase separation (NIPS) method. Optical tests indicate the confinement of CdS QDs in the PS matrix at the smallest bandgap (2.41 eV) with a 5 wt% loading. PS has two prominent emission peaks at 411 and 432 nm, attributed to photoelectron–hole recombination on the surface of pure PSM. The incorporation of 1 wt% CdS QDs into PSM diminished the initial peak and induced a blueshift in the subsequent peak, resulting in the emergence of three emission peaks associated with the near band‐edge emission of confined CdS QDs. The overloading of CdS diminished all emission peaks. Proton exchange membrane water electrolysis (PEMWE) produces oxygen at the anode and hydrogen at the cathode by transporting protons from the anode to the cathode via a proton exchange membrane (PEM). The efficacy of PEMWE can be enhanced through accelerated catalytic reactions at both electrodes; therefore, the advancement of a PEM with superior ionic conductivity and physicochemical stability is imperative. Nafion, a perfluoro‐sulfonic acid polymer, is the predominant material utilized for PEMs [112]. Nonetheless, despite its superior conductivity and chemical stability, it demonstrates elevated hydrogen permeability owing to its structural attributes (Figure 6). QDs possess a hydrophilic functional group that functions as an ion conductor and exhibit remarkable compatibility with the hydrophilic cluster of Nafion, attributable to their distinctive nanoscale structure.

FIGURE 6.

Schematic representation of the N‐doped CQD‐coated Nafion membranes. Reproduced from reference [112]. Copyright (2023), with permission from American Chemical Society.

Metal oxide QDs, including TiO₂ and ZnO, merge the advantages of nanoscale metal oxides with quantum confinement phenomena. TiO₂ QDs demonstrate robust photocatalytic efficacy, chemical stability, and ultraviolet responsiveness, whereas ZnO QDs offer antibacterial characteristics and improved hydrophilicity. The integration of metal oxide QDs into polymeric membranes enhance water permeability, resistance to fouling, and photocatalytic self‐cleaning properties. These QDs are especially beneficial in wastewater treatment, where the concurrent separation and degradation of contaminants is necessary. Furthermore, their powerful interfacial contact with polymer chains improves mechanical durability, alleviating prevalent problems of cracking or swelling in high‐performance membranes. Researchers can improve metal oxide QDs for multifunctional performance by adjusting particle size, surface chemistry, and loading concentration, without substantially sacrificing selectivity.

Doped and surface‐FQDs serve as a method to augment membrane performance by including heteroatoms, surface ligands, or functional groups that facilitate specialized interactions with target molecules or environmental inputs. N‐CQDs, sulfur‐doped GQDs, and functionalized semiconductor quantum dots have been employed to adjust hydrophilicity, charge density, and reactivity. Amino‐functionalized CQDs on chitosan membranes augment metal ion binding, whereas carboxyl‐terminated GQDs boost antifouling properties and ionic selectivity. Surface functionalization facilitates the integration of stimuli‐responsive characteristics, allowing membranes to react to variations in pH, temperature, or light intensity. Doped QDs merge the inherent multifunctionality of the base material with enhanced chemical specificity, hence broadening the design possibilities for membranes that incorporate separation, sensing, catalytic, and antimicrobial capabilities within a unified platform.

The selection of QD type, dimensions, surface chemistry, and loading methodology must be meticulously customized to the polymer matrix and intended application to optimize performance while guaranteeing stability and safety (Table 2). This expanding research emphasizes the crucial function of QDs in enhancing PNC membranes from conventional passive fillers to multifunctional, intelligent, and adaptable materials appropriate for diverse separation, environmental, and medicinal applications.

TABLE 2.

Types of QDs in polymer nanocomposite membranes.

QDs type	Example materials	Polymer matrices	Functional advantages	Applications	Surface functionalization/ Doping	Challenges	Reference
Carbon QDs	CQDs, N‐doped CQDs	PVDF, PES, PSF, PVA, Chitosan	Hydrophilicity, antifouling, antimicrobial, photoluminescence	Water purification, sensing, antifouling membranes	Amino, carboxyl, hydroxyl groups	Photostability, leaching	[113, 114, 115, 116, 117, 118]
Graphene QDs	GQDs, S‐doped GQDs	PVDF, PVA, Chitosan	Mechanical reinforcement, hydrophilicity, charge‐based separation, optical sensing	Water treatment, ionic separations, antibacterial membranes	Amino, carboxyl, sulfur groups	Restacking, aggregation	[119, 120, 121, 122, 123, 124, 125]
Semiconductor QDs	CdSe, ZnS, PbS	PVDF, PSF, PVA	Photocatalytic, antimicrobial, tunable bandgap	Pollutant degradation, antibacterial membranes, sensing	Ligand functionalization, polymer grafting	Toxicity (Cd, Pb), leaching	[112, 114, 126, 127, 128, 129, 130]
Metal Oxide QDs	TiO2 QDs, ZnO QDs	PVDF, PES, PSF	Photocatalytic self‐cleaning, antimicrobial, hydrophilicity	Waste water treatment, antifouling membranes	Surface hydroxylation, ligand coating	UV stability, aggregation	[131, 132, 133, 134]
Doped / Functionalized QDs	N‐, S‐, B‐, P‐doped CQDs/GQDs; surface‐modified CdSe	PVDF, PVA, Chitosan, PSF	Stimuli‐responsive, metal ion adsorption, enhanced charge selectivity	Smart membranes, ion‐selective membranes, responsive sensing	Amino, carboxyl, thiol, polymer grafting	Synthesis complexity, stability	[135, 136, 137, 138]

5. Interfacial Engineering

Interfacial engineering is crucial in influencing the performance of polymer–QDs nanocomposite membranes, as the interface regulates dispersion, stability, transport characteristics, and the conversion of intrinsic QDs qualities into macroscopic membrane functionalities. In contrast to traditional fillers, QDs exhibit a high density of surface atoms and functional groups, rendering their interaction with polymer chains acutely sensitive to surface chemistry. Ligand exchange and surface functionalization are thus essential processes in the creation of QD‐based membranes. The as‐synthesized QDs are frequently coated with tiny organic ligands that stabilize them in solution, however may be incompatible with polymer matrices. Ligand exchange methodologies, including the substitution of hydrophobic ligands with hydrophilic or polymer‐compatible entities, facilitate enhanced dispersion and augmented interfacial adhesion. Amino‐, carboxyl‐, or hydroxyl‐functionalized CQDs and GQDs readily engage with polar polymers such as PVA, chitosan, and PA, whereas customized surface ligands facilitate their integration into more hydrophobic matrices like PVDF or PSF. In semiconductor and metal oxide QDs, surface functionalization also functions to reduce toxicity and inhibit leaching by securely attaching the QDs within the polymer matrix.

At the polymer–QD interface, various contact mechanisms may concurrently function, including hydrogen bonding, electrostatic attraction, and covalent bonding. Hydrogen bonding is especially significant in CQDs, where many surface oxygen or nitrogen groups engage with polymer chains, improving compatibility and minimizing interfacial gaps. Electrostatic interactions are significant when charged QDs are included within oppositely charged or zwitterionic polymers, facilitating stable dispersion and, in certain instances, charge‐selective transport. Covalent bonding, albeit less prevalent because to synthetic intricacies, offers superior interfacial anchoring and is particularly beneficial for applications necessitating long‐term stability in tough operational environments. The covalent attachment of QDs to polymer backbones or crosslinked networks reduces nanoparticle movement and guarantees stable membrane performance over prolonged usage.

Effective control of dispersion and aggregation continues to be a fundamental problem in QD‐based nanocomposite membranes (Figure 7). The diminutive size of QDs intrinsically diminishes sedimentation propensity relative to bigger nanoparticles; yet, aggregation may still transpire due to robust van der Waals interactions or inadequate surface stability. Aggregated QDs may obstruct pores, induce nonselective defects, or reduce active surface area, so undermining permeability and selectivity. Strategies for interfacial engineering, including surface charge modulation, steric stabilization by polymer grafting, and regulated in situ development of QDs inside polymer matrices, have been utilized to mitigate these challenges. In situ synthesis specifically facilitates uniform dispersion by producing QDs immediately within the polymer phase, thus preventing aggregation during mixing and enhancing interfacial contact.

FIGURE 7.

Schematic illustrations of interfacial engineering strategies in polymer–QDs nanocomposite membranes, highlighting (a) ligand exchange and surface functionalization, (b) dominant interfacial interaction mechanisms, (c) dispersion versus aggregation behavior, and (d) the influence of quantum dot (QD) size and loading on membrane structure and performance.

The concentration and size of QDs significantly affect interfacial behavior and membrane performance. Under low to moderate load conditions, well‐dispersed QDs can augment hydrophilicity, establish supplementary transport routes, and impart active capabilities without compromising membrane integrity. Excessive QD loading frequently results in aggregation, pore obstruction, or heightened brittleness, highlighting the necessity for meticulous regulation of filler concentration. Likewise, QD size influences both interfacial interactions and functional efficacy. Smaller QDs provide a greater surface area and stronger interactions with polymers, promoting uniform dispersion and improved functionality, while larger QDs may resemble traditional nanoparticles, heightening the likelihood of interfacial defects. Notwithstanding considerable advancements, issues regarding interfacial compatibility remain, especially in the integration of QDs into hydrophobic polymers or high‐performance membranes functioning under harsh circumstances. The disparity in surface energy, inadequate ligand stability, and prolonged chemical degradation may compromise the polymer–QD interface, resulting in leaching or diminished performance. Confronting these problems necessitates a comprehensive interfacial engineering strategy that takes into account QD chemistry, polymer architecture, fabrication techniques, and operational conditions. Ultimately, rational interfacial design is the crucial enabling feature that allows QDs to serve not just as fillers but as active components that confer stability, multifunctionality, and responsiveness to PNC membranes. Membranes of polymer carbon dots (PCDs) with various acid groups were engineered to regulate electrostatic complexation. The enhanced interface compatibility provides PCDMs with a maximum PCD content of 50 wt%, while phosphate‐functionalized PCDs offer numerous proton transport sites and a minimal energy barrier for proton transport pathways [139]. A chitosan (CH)‐CDs hybrid hydrogel nanocomposite film was subsequently developed as a membrane platform for the extraction of Cd²⁺ ions from wastewater. The synthesized CH‐CDs membranes have commendable mechanical properties, characterized by stress resistance and flexibility to enhance handling. The equilibrium state was attained within 5 min. The UV‐light illuminations significantly increased the Cd²⁺ removal efficiency of the photoluminescent CDs, achieving a rate four times faster [140]. α‐amino‐substituted lysine derivatives with a defined chemical structure were utilized as precursors to synthesize bright and extremely stable fluorescent carbon dots via a simple hydrothermal method [141]. The correlations between the chemical structure of precursors, circular dichroism fluorescence, and particle size were examined. The findings demonstrated that a higher quantity of functional groups in precursors might enhance the degree of cross‐linking, resulting in reduced size, improved fluorescence characteristics, and increased stability of CDs. CDs exhibited excitation‐dependent excitation‐dependent dual excitation and dual emission (DE2) fluorescence (Figure 8). The DE2 fluorescence characteristic can be ascribed to the recurrent structural units that can establish a distinct donor‐π‐acceptor (D‐π‐A) configuration, with C–N, –NH₂, and C–OH serving as electron‐donating moieties and C=O functioning as an electron‐accepting moiety.

FIGURE 8.

Repeated structural units as donor‐π‐acceptor (D‐π‐A) architectures in the polymerization structure. Reproduced from reference [141]. Copyright (2020), with permission from American Chemical Society.

Control of airborne diseases and pollution generally requires numerous membranes, each designed for effective aerosol filtering, moisture management, or antimicrobial defense. Consolidating all these activities into a singular membrane is significantly beneficial however remains intrinsically difficult due to material incompatibility and unavoidable performance compromise. Another work revealed a photoactive Janus nanofibrous membrane designed for highly efficient air filtration, fabricated using successive electrospinning [142]. This asymmetric membrane incorporates a biomimetic cactus spine and pollen structures within a hydrophilic biopolymer matrix, embedding N‐CQDs on one side and hydrophobic microchannels on the opposite side, thereby establishing interfacial chemical gradients that facilitate unidirectional water transport (Figure 9). The nanofibrous membranes demonstrate concurrent size‐exclusion screening and electrostatic capture via quantum‐confined charge polarization, attaining over 99.59% retention of PM0.3 aerosols.

FIGURE 9.

(A,B) Schematics and fluorescence images of antigravity directional water transport across PVDF/PG‐N20 membranes under UV radiation using 1% sodium fluorescein‐labeled droplets, (A) discharge of dye droplets from the hydrophobic PVDF side to the hydrophilic PG‐N20 side and (B) attempted discharge of dye droplets from the hydrophilic side to the hydrophobic side. Real‐time force on water droplets versus distance when dropped on (C) PVDF side and (D) PG‐N20 side of the PVDF/PG‐N20 membranes. (E) WVTR of PVDF/PG‐N20 membranes. (F) Schematic illustration of the proposed water transport mechanism in the PVDF/PG‐N20 membranes with asymmetric wettability, PLO: capillary force in hydrophobic channels, PLI: capillary force in hydrophilic channels. Reproduced from reference [142]. Copyright (2025), with permission from American Chemical Society.

6. Biocompatibility of QDs in Polymer Nanocomposite Membranes

The biocompatibility of QDs is a critical parameter in evaluating their suitability for applications involving water purification, biomedical interfaces, and antimicrobial surfaces. QDs induced biological responses are strongly dependent on composition, size, surface chemistry, and colloidal stability. Semiconductor QDs containing heavy metals like cadmium or lead can demonstrate cytotoxicity due to ion release, activation of oxidative stress, and intracellular accumulation [143]. These risks are particularly relevant under conditions where polymer degradation or nanoparticle leaching may occur. Metal oxide QDs, such as TiO₂ and ZnO, usually show improved biocompatibility; however, their photocatalytic activity can produce ROS, which, although advantageous for antimicrobial properties, may also cause oxidative damage in mammalian cells under uncontrolled exposure [144]. Therefore, dose‐dependent and context‐specific evaluation is necessary. CQDs and GQDs have been considered to be safer alternatives owing to their metal‐free composition, useful aqueous dispersibility, and adjustable surface functionalization [145, 146]. Multiple studies indicate low cytotoxicity profiles at concentrations relevant to operational conditions, especially when surface‐passivated or heteroatom‐doped to improve stability. In polymer–QDs nanocomposite membranes, biocompatibility is intricately associated with the stability of nanoparticle immobilization. Robust interfacial bonding, covalent attachment, or in situ synthesis within the polymer matrix can minimize nanoparticle migration and reduce exposure risks. Thus, the incorporation of safe‐by‐design principles encompassing material selection, surface engineering, and leaching validation will be pivotal in ensuring the responsible advancement of multifunctional QDs enabled membrane systems.

7. Multifunctional Applications

7.1. Water and Wastewater Treatment

Multifunctional polymer–QDs nanocomposite membranes have garnered increasing interest in water and wastewater treatment for their capacity to combine separation with supplementary active functionalities, including antifouling, antibacterial properties, photocatalysis, and sensing. Traditional polymer membranes employed in microfiltration, UF, NF, and reverse osmosis function predominantly as passive barriers, utilizing size exclusion or charge interactions to eliminate impurities [147]. Although efficient, these membranes are particularly vulnerable to fouling from organic substances, bacteria, and inorganic compounds, resulting in decreased flux, the necessity for frequent chemical cleaning, and a shortened operating lifespan. The integration of QDs into polymer membranes provides a means to address these limitations by adding multifunctionality without fundamentally changing existing membrane production methods. In water and wastewater treatment, QDs, including CQDs, GQDs, semiconductor QDs, and metal oxide QDs, have demonstrated a substantial improvement in membrane hydrophilicity, a crucial element in minimizing fouling. The many surface functional groups on CQDs and GQDs facilitate robust interactions with water molecules, creating hydration layers that inhibit the adsorption of organic foulants and proteins [31, 81]. Consequently, QD‐modified membranes often demonstrate enhanced water flow, superior flux recovery ratios, and less irreversible fouling relative to unmodified polymer membranes. These enhancements are especially beneficial for the treatment of intricate wastewater streams comprising natural organic materials, colors, oils, and surfactants. In addition to passive antifouling properties, QD‐based membranes have active antibacterial capability, essential for reducing biofouling. Semiconductor and metal oxide QDs, including ZnO and TiO₂, can produce ROS upon light exposure, resulting in bacterial inactivation on membrane surfaces. Certain CQDs demonstrate inherent antibacterial properties through membrane rupture or oxidative stress processes, even in the absence of light. QD‐modified membranes inhibit microbial adhesion and biofilm development, ensuring consistent long‐term efficacy and minimizing the necessity for rigorous cleaning procedures, thereby tackling a significant obstacle in wastewater treatment processes. Photocatalytic activity constitutes a significant multifunctional benefit of QD‐integrated membranes. Titanium dioxide (TiO₂), zinc oxide (ZnO), and certain semiconductor QDs incorporated into polymer matrices facilitate the concurrent filtration and degradation of organic contaminants, including colors, medicines, and endocrine‐disrupting substances. Under UV or visible light, these QDs facilitate the degradation of pollutants at or near the membrane surface, thereby decreasing pollutant accumulation and alleviating fouling. The dual separation and degradation capacity is especially appealing for advanced wastewater treatment and reuse applications, where trace organic pollutants present considerable environmental and health hazards. QD‐based membranes provide options for the selective extraction and monitoring of certain pollutants. Functionalized CQDs and GQDs can be engineered to preferentially interact with heavy metal ions, like lead, mercury, or copper, via coordination with surface functional groups. This facilitates improved rejection or adsorption of hazardous metals during filtering. The inherent photoluminescence of QDs enables membranes to serve as optical sensors, delivering real‐time feedback on membrane fouling, pollutant breakthrough, or alterations in water quality. Sensing‐enabled membranes signify a progressive advancement in intelligent water treatment systems.

Solvent resistant nanofiltration (SRNF) membranes are in high demand for processing organic solutions, particularly those containing big molecules with molecular weights ranging from 200 to 2000 Da; nonetheless, they exhibit several disadvantages, including generally inadequate solvent resistance and low solvent permeance. Li et al. introduced a novel category of amino‐functionalized graphene quantum dots (aGQDs) incorporated into thin film nanocomposites (TFN) for SRNF membranes, fabricated using IP and subsequent processes including chemical imidization, crosslinking, and solvent activation [148]. The fabricated membranes facilitated covalent connections between the IP skin layer and the substrate, as well as between the IP layer and the included aGQDs. The ethanol permeance and surface porosity enhanced by 44% and 69%, respectively, with the incorporation of aGQDs under ideal circumstances, whereas the rejection of Rhodamine B (RDB, 479 Da) remained consistently above 99%. Moreover, these innovative membranes demonstrated exceptional long‐term durability, with a rejection rate over 99% for Rose Bengal (RB, 1017 Da) during the continuous filtering of a 100  mg L⁻¹ RB/N, N‐dimethyl formamide (DMF) solution at ambient temperature for over 768 h. Li et al. presented a polyimide (PI)‐based TFN membrane incorporated with GQDs, demonstrating enhanced solvent resistance for organic solvent nanofiltration (OSN) applications. The SRNF membrane, designated as (PI‐GQDs/PI)XA, was manufactured using sequential steps of IP, imidization, cross‐linking, and solvent activation. The IP process was conducted on the PI substrate surface using an aqueous m‐phenylenediamine solution infused with GQDs, averaging 1.9 nm in size, and an n‐hexane solution of 1,2,4,5‐benzenetetracarboxylic acyl chloride (Figure 10). The created (PI‐GQDs‐50/PI)X SRNF membranes, devoid of organic solvent activation, attained an ethanol permeance approximately 50% superior to that of the GQD‐free membranes under identical preparation conditions, with no observable compromise in dye rejection.

FIGURE 10.

Long‐term solvent resistance of (PI‐GQDs‐50/PI)XA membranes. (a) During 100 h cross‐flow filtration with RB/DMF solution (100.0 mg L⁻¹) as the feed at room temperature, (b) static immersion for more than 120 h in DMF at 80°C, and (c) static immersion test in organic solution at room temperature for nearly 1 year; (A) Before immersion in DMF, (B) after static immersion in DMF for 356 days, (C) before immersion in ethanol, and (D) after static immersion in ethanol for 363 days. Reproduced from reference [149]. Copyright (2019), with permission from American Chemical Society.

Bi et al. devised an innovative method for the design and fabrication of NF membranes via pore engineering with GQDs. An in‐situ IP reaction occurred between GQDs and TMC within the pores of UF membranes, subsequently followed by thermal treatment [108]. The irreversible contraction of membrane bulk material due to thermal treatment guaranteed the stable retention of the GQDs nanoaggregates. The voids within GQD nanoaggregates created the holes of the resulting membranes, with a radius that can be adjusted between 1.21 and 1.72 nm by varying the quantity of GQDs added. The resulting membranes demonstrated an ultrafast water penetration rate of 244.7 [L/(m² h bar)], approximately 5–6 times greater than previously reported data, with rejection rates for Alcian blue and Congo red reaching 92.9% and 98.8%, respectively. A bespoke loose nanocomposite membrane was developed to assess the viability of efficient dye/salt separation in actual pretreatment hairwork dyeing effluent (HDE). It was noted that following the partial alternative doping of 4,4′‐bipiperidine and the continuous incorporation of GQDs, the ensuing membrane skin‐layer characteristics, including smoothness, hydrophilicity, surface charge, and nominal pore size, were enhanced synergistically [150]. Thus, the ideal TFN‐0.2 membrane exhibited exceptional fractionation and antifouling capabilities for synthetic dye/salt mixes and actual pretreatment HDE. The as‐prepared TFN‐0.2 membrane had the maximum water permeance of 56.0 L·m⁻²·h⁻¹·bar⁻¹, with a retention rate for all selected dyes of at least 99.8% and a salt permeability of at least 91.2%. Furthermore, the antifouling indices for reversible and irreversible fouling ratios of the TFN‐0.2 membrane in relation to the HDE solution decreased from 13.3% and 20.7% of the pristine membrane to 8.32% and 1.34%, respectively. The flux recovery ratio significantly increased from 79.1% to 98.5% throughout this period. High‐flux β‐CD/GQDs NF membranes were synthesized using IP, utilizing β‐CD as the aqueous monomer, GQDs as the additive, and TMC as the organic monomer [151]. The incorporation of GQDs not only altered the membrane surface characteristics but also resulted in the development of a porous selective layer due to nonspecific hydrogen bonding interactions between GQDs and β‐CD. The pure water flux of the β‐CD/GQDs NF membranes rose from 122.2 to 474.7 (L/m²h) (at a pressure of 0.1 MPa) as the concentration of GQDs grew from 0 to 0.5 wt%, about 3.9 times more than that of the pristine β‐CD membrane. Lamellar membranes exhibit significant potential for extremely selective permeation, particularly those based on graphene, which are extensively researched. Graphene‐based membranes have restricted molecular permeance due to the adverse microenvironments of nanochannels, primarily characterized by singular chemical affinity and constrained channel dimensions [152]. QDs were incorporated into nanochannels to regulate the microenvironments for enhanced performance. Hydrophobic GQDs were affixed within hydrophilic GO nanochannels to enhance affinity for nonpolar molecules and locally increase the channel size from 0.84 to 1.35 nm. The favorable interaction enables swift breakdown and ingress of molecules into nanochannels, while the increased channel dimensions enhance their speedy transport. This synergistic action enables significantly improved permeance for both polar and nonpolar molecules, particularly for nonpolar molecules.

7.2. Gas Separation and Barrier Membranes

Conventional polymeric gas separation membranes predominantly operate based on the solution‐diffusion process, wherein gas transport is dictated by the mobility of polymer chains and the availability of free volume. Although polymers including polyimides, PSFs, polyethylene, and ethylene–vinyl alcohol copolymers are extensively utilized, they frequently exhibit restricted selectivity, plasticization phenomena, and a decline in permeability over time. The integration of QDs introduces nanoscale interfacial effects that can alter gas transport paths and introduce supplementary functional mechanisms, resulting in higher separation performance and improved barrier qualities. In gas separation membranes, CQDs and GQDs are notably effective in modifying the free volume distribution inside the polymer matrix. Their diminutive size and robust interfacial interactions disturb local polymer chain arrangement, generating regulated micro voids that promote selective gas diffusion. This phenomenon has been utilized to augment permeability for tiny gases like as CO₂, H₂, and O₂, while preserving or enhancing selectivity for larger molecules like N₂ or CH₄. Furthermore, surface‐FQDs can facilitate particular interactions with target gasses (Figure 11). Oxygen‐containing functional groups on CQDs demonstrate an affinity for CO₂ via dipole–quadrupole interactions, enhancing CO₂ permeability and selectivity in gas separation membranes. In barrier membrane applications, especially in food packaging and protective coatings, QDs function by an alternative mechanism. Well‐dispersed QDs augment the tortuosity of gas diffusion paths, compelling gas molecules to traverse longer and more intricate routes through the membrane. This markedly lowers gas transmission rates, enhancing the effectiveness of oxygen and moisture barriers. GQDs are particularly efficient in this capacity owing to their planar architecture and robust interfacial adhesion, which establish highly convoluted diffusion pathways even at minimal loading levels. In contrast to traditional inorganic fillers, QDs attain these characteristics without significantly impairing membrane transparency or mechanical flexibility, both of which are essential for packaging applications. Semiconductor and metal oxide QDs enhance functionality by facilitating stimulus‐responsive gas barrier properties. Under light irradiation, specific QDs can modify polymer chain dynamics or induce localized heating, briefly affecting gas permeability. This creates prospects for intelligent barrier membranes that can react to environmental circumstances. Furthermore, QDs enhance resistance to gas‐induced plasticization, such as that caused by CO₂, by stabilizing polymer chains through robust interfacial contacts and mitigating long‐term performance deterioration.

FIGURE 11.

Mechanism of gas separation and barrier proeprties of QDs based nanocomposite membranes: (a) solution–diffusion in neat polymer membranes, (b) QD‐induced tortuous pathways for barrier membranes, (c) selective gas transport via QDs–gas interactions (e.g., CO₂ affinity), and (d) stabilized polymer chains at the polymer–QDs interface reducing plasticization.

i‐TFN membranes, using nanomaterials as the interlayer, have garnered increasing interest from researchers in recent years due to their efficacy in modulating the structural configuration of the separation layer inside the membrane separation domain. Another study involved the synthesis of amino‐functionalized graphene quantum dots (N‐GQDs) and their application as an interlayer to enhance the PES UF substrate [110]. Subsequently, IP was conducted between TMC and β‐CD to synthesize innovative i‐TFN polyarylate membranes for CO₂/N₂ separation. The impact of the N‐GQDs deposition quantity on the structure and gas separation efficacy of the composite membrane was extensively examined. The findings demonstrated that the i‐TFN polyarylate membrane had a distinct sandwich structure and facilitated an efficient transport pathway for CO₂ diffusion. Furthermore, the interaction between the nitrogen‐containing groups (e.g., amino and amide groups) in the i‐TFN membrane and CO₂ molecules enhanced the CO₂/N₂ separation selectivity. FQDs were integrated to modulate the physicochemical characteristics of interlaminar nanochannels for efficient molecule separation. FQDs functioning as hard nanowedges can expand the interlaminar nanochannels for rapid molecular transport [153]. The hydrophilic functional groups of FQDs promote the preferential transit of water molecules across the interlaminar nanochannels. The improved GO‐FQDs/PTFE membrane achieves an exceptional permeation flux of 8877.8 [g/(m²h)] and a favorable separation factor of 3763 when processing a 90 wt% n‐butanol aqueous solution at 80°C, exhibiting performance superior to any previously reported GO‐based laminar membranes. Three functionalized CQDs with carboxyl, amino, and sulfonic acid groups were produced and subsequently integrated into the PA layer of TFN membranes using IP [154]. The effects of functional groups of CQDs on membrane characteristics were carefully examined. Leveraging the superior hydrophilicity and diminutive size of CQDs, all TFN membranes containing CQDs demonstrated enhanced permeate flux, while maintaining Na₂SO₄ rejection efficiency and exhibiting improved antifouling properties compared to the TFC membrane. A hybrid sulfonated poly(ether ether ketone) (SPEEK) nanofiber was synthesized for the first time by consistently incorporating 2–5 nm QDs [155]. Subsequently, chitosan was integrated into the pores of the fiber mat to fabricate a hybrid nanofiber composite membrane (HNFCM). The filled QDs can offer a substantial quantity of proton‐conducting moieties (–NH–/–NH₂ and –COOH). The –NH–/–NH₂ groups create structured acid–base pairs with the –SO₃H groups in SPEEK, facilitating low‐energy routes for proton transfer within the nanofiber. The hyperbranched macromolecule (HBM) PA PEM, characterized by a consistent three‐dimensional matrix architecture, enhances proton conductivity [156]. To boost the utilization of HBM in direct methanol fuel cells (DMFC), GO, and GQDs are integrated into HBM to improve the proton/methanol selectivity of the membrane. The functional groups on the surfaces of GO and GQD will interact with –SO₃H groups in HBM through hydrogen bonding and contribute to the formation of proton conductive channels. The GO and GQD in the composite can effectively inhibit the penetration of methanol molecules. Parthiban et al. investigated CQDs as a prospective inorganic filler to develop a Nafion hybrid membrane, significantly reducing methanol crossover for DMFCs [157]. Highly fluorescent CQDs are manufactured by a straightforward hydrothermal procedure utilizing gelatin as the precursor, with their production validated by UV–visible and photoluminescence spectroscopic analyses. The incorporation of CQDs enhances ionic conductivity mainly through the creation of hydrogen bonds between the many hydrophilic groups present in the CQDs and the sulfonic acid moieties inside the Nafion matrix. Polymer QDs with intrinsic ordered acid–base pairs are employed and affixed to dopamine‐coated GO, so creating long‐range conductive channels. The generated building blocks (nPGO) are incorporated into a sulfonated poly(ether ether ketone) matrix to produce composite membranes [158]. The engineered long‐range transfer highways with organized acid–base pairs confer substantial enhancement to the proton conduction capability of the composite membrane. In the hydrated condition, the composite membrane exhibits a 91% enhancement in conductivity compared to the control membrane, while the single‐cell fuel utilizing the membrane realizes a 71% rise in maximum power density. Under anhydrous circumstances, the composite membrane exhibits a significant increase in conductivity, attaining 7.14 mS cm^–1, nearly tenfold the conductivity of the control membrane (0.78  mS cm^–1). Notably, the anhydrous proton conduction performance is comparable to that of composite membranes infused with ionic liquids, a feat difficult to achieve with traditional fillers.

7.3. Antibacterial and Antifouling Membranes

Biofouling and microbiological contamination continue to be significant obstacles that hinder the long‐term efficacy and reliability of membrane‐based separation systems in water treatment, biomedical devices, and healthcare‐related applications. The attachment and growth of microorganisms on membrane surfaces result in pore obstruction, decreased flow, elevated transmembrane pressure, and recurrent chemical cleaning, eventually diminishing membrane longevity and escalating operating expenses. The antifouling capability of QDs is significantly influenced by their functional groups, which enhance their hydrophilicity and impart a negative surface charge. This result in the formation of a hydration layer barrier and generates electrostatic repulsion against a range of foulants. He et al. reported that changing a PES membrane with Na⁺‐modified CQDs enhanced the hydrophilicity of the NF membrane, hence improving its antifouling characteristics [84]. The CQDs‐Na/PES NF membrane demonstrated significant hydrophilicity and flux due to the protective hydration layer formed by the hydrophilic CQDs‐Na selective layer. The numerous hydroxyl and carboxyl groups present in the CQDs created robust intermolecular bonds with the PA skin layer, leading to improved long‐term stability, with no notable leaching of CQDs observed after 180 h of filtration. Heng and coworkers documented enhanced antifouling characteristics resulting from the doping of a PES membrane with NCQDs [159]. A polyacrylic layer was successfully grafted onto a PES membrane through the process of UV‐induced graft polymerization. The carboxyl and hydroxyl groups in the NCQD‐TiO₂ nanoparticles formed a substantial hydration layer, attributed to the hydrogen bonding interactions between the NCQDs and the adjacent water molecules. The presence of a hydrophilic surface layer effectively suppressed foulant adhesion, particularly for the hydrophobic dye methylene blue, thereby facilitating the facile removal of deposited contaminants from the membrane surface. Owing to their abundant hydrophilic functional groups, CQDs serve as effective dopants for constructing a stable hydration layer on NF membranes, leading to significantly enhanced antifouling performance. The incorporation of oxygen‐containing functional groups in CQDs imparts a net negative surface charge to the host membrane, thereby electrostatically repelling anionic foulants and mitigating their adhesion. For instance, Sun and Wu reported the fabrication of PSF NF membranes incorporating CQDs with diverse surface functionalities, including carboxylated CQDs (CCQDs), N‐CQDs, and sulfonated CQDs (SCQDs), which collectively contributed to improved antifouling performance [154]. PSF membranes incorporating CCQDs and SCQDs exhibited markedly more negative surface zeta potentials as a result of the anionic carboxylate and sulfonate functionalities. This enhanced negative surface charge significantly improved antifouling performance against anionic BSA, as evidenced by reduced total fouling ratios. The resulting electrostatic repulsion effectively suppressed foulant attachment and facilitated the formation of a looser, less compact fouling layer. In contrast, membranes modified with more charge‐neutral NCQDs demonstrated improved resistance toward cationic foulants, attributable to their relatively neutral surface characteristics. Notably, the surface charge of CQD‐modified NF membranes can be readily tuned through rational control of CQD surface functionalities, offering a versatile strategy for optimizing antifouling behavior. In another study, Wu et al. reported comparable antifouling enhancements through the incorporation of L‐aspartic acid functionalized graphene quantum dots (LaGQDs) into a PSF membrane [160]. The presence of LaGQDs suppressed nanoparticle aggregation within the active layer by impeding monomer diffusion into the PSF substrate during aqueous‐phase immersion, thereby producing a smoother selective layer with reduced surface roughness. In addition, the oxygen‐rich functional groups of LaGQDs enhanced membrane hydrophilicity, facilitating the formation of a stable hydration layer that substantially diminished foulant adsorption. Notably, positively charged lysozyme induced significantly greater fouling on the LaGQDs‐free control membrane than on the LaGQDs/PSF membrane, attributable to electrostatic attraction toward the negatively charged control surface. These results underscore the importance of engineering near‐neutral selective layers to effectively mitigate fouling arising from both cationic and anionic species. The incorporation of CQDs into the active layer of polymeric membranes can effectively decrease surface roughness, thereby limiting foulant‐membrane contact and enhancing antifouling performance. In this context, Deng et al. reported the fabrication of a smooth carbo polyetherketone (CPEK) membrane surface through the integration of CQDs using a layer‐by‐layer assembly strategy [161]. The introduction of a CQD‐based surface layer led to a pronounced reduction in membrane surface roughness. Owing to their nanoscale dimensions, CQDs in combination with PEI were densely and uniformly deposited on the membrane surface, effectively masking the prominent PA peaks and ridges of the CPEK membrane. The resulting smoother surface diminished interfacial contact with BSA foulants, thereby enhancing water permeance retention and flux recovery. Notably, simple rinsing with deionized water was sufficient to restore the original water flux, indicating that fouling occurred primarily via a loosely bound foulant layer on the smoothened membrane surface. However, some researches have shown that the incorporation of QDs could enhance the roughness of the membrane surface. For instance, Gai et al. found that CQDs have the potential to either enhance or reduce surface roughness, influenced by the pH levels and the loading of CQDs [162]. Spherical CQDs predominantly functionalized with carboxyl groups (CCQDs) were adjusted to pH 5 or 9 via NaOH treatment, producing charge‐neutral CQDs‐Na5 and alkaline CQDs‐Na9 nanospheres with diameters in the range of 5–9 nm. Incorporation of 1 wt% pristine CCQDs or CQDs‐Na5 resulted in a markedly smoother membrane surface, attributable to dense nanoparticle packing that effectively attenuated PA surface peaks. The relatively acidic nature of CCQDs and CQDs‐Na5 was found to retard the IP process, leading to the formation of finer PA peaks and ridges. Notably, membranes prepared with both low (0.5 wt%) and high (2 wt%) loadings of CQDs‐Na9 also exhibited reduced surface roughness compared with the pristine PES membrane. The 0.5 wt% loading led to reduced diffusion of aqueous monomers into the organic phase, producing small PA peaks that are closely packed, resulting in decreased surface roughness. The loading of 2 wt% CQDs‐Na9 led to the formation of large PA nodules, which subsequently decreased the surface roughness. The findings suggest that adjusting the acidity of the membrane solution and the content of CQDs can effectively reduce surface roughness, leading to enhanced antifouling performance. In a study Xu et al. reported that the incorporation of 0.05 wt% GQDs into the active layer of a polyacrylonitrile (PAN) membrane led to an increase in both surface roughness and hydrophobicity [163]. Strong covalent interactions between the GQDs and PEI resulted in the formation of large GQDs‐PEI aggregates that persisted following IP. These agglomerates generated pronounced surface grains, increasing the surface roughness to nearly four times that of the pristine NF membrane. The elevated roughness intensified foulant/membrane contact, thereby potentially compromising antifouling performance. In addition, the GQDs/HPAN membrane exhibited diminished hydrophilicity, attributed to the presence of hydrophobic aromatic domains within the GQDs. These findings suggest that selecting aqueous‐phase monomers with weaker affinity toward GQDs, along with synthesizing GQDs enriched in oxygen‐containing functional groups, is critical for achieving a smooth, hydrophilic selective layer conducive to antifouling applications.

Different QDs demonstrate remarkable photocatalytic capabilities that improve chemical and biological antifouling processes. Qiu et al. combined graphitic carbon nitride (CN) nanosheets with graphene sheets that were intercalated with Ag nanospheres and carbon nitride QDs (CNQDs) to produce a self‐cleaning membrane [164]. The CNQDs‐modified thin‐film membrane demonstrated outstanding photocatalytic performance, as evidenced by the complete degradation of rhodamine B under UV–visible irradiation. In this system, CNQDs facilitated the generation of photoinduced electron–hole pairs, while the Ag/graphene component effectively suppressed charge carrier recombination. The synergistic interaction between these components enhanced the production of ROS, which in turn drove the efficient photocatalytic degradation of rhodamine B. Comparable photodegradation behavior was also observed for methylene blue, indicating effective antifouling performance with minimal dye accumulation within the nanogaps of the CNQDs‐modified thin‐film membrane. These findings collectively demonstrate that photocatalytic nanomaterials represent promising membrane dopants for imparting intrinsic antifouling functionality.

Biofouling, caused by the attachment, growth, and accumulation of microorganisms, particularly bacteria on membrane surfaces, severely limits membrane performance [165]. Consequently, the development of antibacterial membranes has emerged as a key strategy to mitigate this challenge. The bactericidal effects of QDs have been documented in several investigations [166, 167]. The antibacterial efficacy of the QDs is dependent upon their surface charge and particle size, whereas surface functionalization can regulate this process [168]. Most polymer membranes are inherently hydrophobic, making them highly susceptible to microbial contamination and severe membrane fouling. Bacterial adhesion to solid surfaces occurs naturally and can initiate biofilm formation, exacerbating performance decline [169]. Incorporating QDs into membranes offers a promising strategy for long‐term fouling mitigation in forward osmosis (FO) applications. Many QDs possess intrinsic antibacterial activity due to the negatively charged carboxyl groups on their surfaces, which induce electrostatic repulsion between the membrane and bacterial cells. Typically, bacterial cell surfaces carry a net negative charge arising from the presence of peptidoglycans in their cell walls [170, 171], further enhancing the antifouling effect of QDs modified membranes. Furthermore, QDs have the capability to directly influence bacterial cells on the membrane surface due to their extremely small size and large surface area. Zhao et al. utilized CQDs derived from citric acid on a PES substrate surface with PDA containing amine groups, resulting in a negatively charged solution that improved antibacterial properties [170]. Membranes exhibiting reduced fouling from microbial or bacterial adhesion demonstrate enhanced water permeability and improved reverse salt flux, owing to the favorable modification of surface properties that promote increased water molecule attraction to the membrane interface [172]. Mahat et al. demonstrated the successful development of a TFC CQDs‐PSF membrane for FO applications [173]. Incorporation of CQDs into the PSF matrix markedly enhanced the membrane surface hydrophilicity and porosity, leading to improved water permeability. Moreover, the CQDs–PSF membrane exhibited potential antibacterial activity against Escherichia coli (Gram‐negative), contributing to superior antifouling performance in FO processes. Koulivand and group fabricated antifouling and antibacterial membranes by incorporating nitrogen‐doped carbon dots (NCDs) into the PES polymer matrix via the phase inversion method [83]. Antibacterial evaluation revealed that membranes containing NCDs at concentrations above 0.10 wt% exhibited measurable antibacterial activity. The inhibition zone diameter increased with higher NCD loading, with membranes containing 0.50 and 1.00 wt% NCDs demonstrating the most pronounced antibacterial performance. Liu et al. reported that a TFN membrane incorporating only GQDs exhibited negligible antibacterial activity against Escherichia coli (E. coli), with significant bacterial inactivation (∼80%) observed only at a high GQDs concentration of 9 g/L [174]. Interestingly, UV irradiation in the presence of GQDs resulted in lower bactericidal efficiency compared to membranes without GQDs, likely due to the absorption of high‐energy photons by the GQDs. In contrast, compositing GQDs with photocatalytic ZnO markedly enhanced antibacterial performance, achieving near‐complete E. coli inactivation within 5 min. The synergistic effect arises from GQDs facilitating interfacial charge transfer in ZnO, promoting the formation of additional electron–hole pairs and generating increased ROS. Covalent immobilization of graphene oxide quantum dots (GOQDs) onto amino‐functionalized PVDF membranes has produced a novel nanocarbon functionalized membrane with significantly enhanced antibacterial and antibiofouling properties. Zeng et al. reported that incorporating GOQDs into a PEG/PVDF NF membrane reduced bacterial activity by 89%, representing a 28% improvement compared to membranes modified with GO sheets [171]. Continuous filtration tests using feedwater containing E. coli revealed a relative flux decline of only 23% for GOQDs‐modified PVDF, markedly lower than the 86% and 62% drops observed for pristine PVDF and GO‐sheet‐modified PVDF, respectively, after 10 h of operation. The GOQD coating effectively inactivates E. coli and Staphylococcus aureus while suppressing biofilm formation on the membrane surface, demonstrating superior antimicrobial and antibiofouling performance compared to previously reported 2D GO sheets and 1D CNT‐modified membranes. The exceptional activity of GOQDs is attributed to their unique structure and uniform dispersion, which maximize exposure of active edges and promote oxidative stress‐mediated microbial inactivation. It is important to recognize that addressing microbial fouling cannot rely solely on enhancing the intrinsic antibiofouling properties of membranes. To prevent rapid membrane fouling, pretreatment of feedwater is typically required, which removes the majority of bacteria; however, residual microorganisms can still form biofilms on the membrane surface. The role of an antifouling membrane is not to completely eliminate bacterial adhesion but to slow biofilm formation. Once biofilms compromise membrane performance, cleaning via chemical or physical methods becomes necessary. Membranes with reduced fouling propensity, however, require less frequent cleaning, thereby lowering operational and maintenance costs. The incorporation of QDs into polymer membranes offers a versatile strategy to enhance both antibacterial and antibiofouling performance. By modulating surface charge, hydrophilicity, and photocatalytic activity, these nanomaterials can significantly slow biofilm formation and reduce microbial adhesion, improving membrane longevity and operational efficiency.

7.4. Photocatalytic and Self‐Cleaning Membranes

Photocatalytic and self‐cleaning membranes signify a significant progression in membrane technology, especially for applications where fouling and enduring organic pollutants restrict long‐term efficacy. Traditional polymer membranes employed in water treatment and separation procedures largely function as passive barriers and are susceptible to fouling by organic substances, bacteria, and inorganic deposits. Fouling diminishes permeation flux and selectivity, while also requiring frequent chemical cleaning, hence reducing membrane longevity and elevating operational expenses. Incorporating photocatalytically active QDs onto polymer membranes offers an efficient method to achieve self‐cleaning properties while maintaining the advantageous mechanical flexibility and processability of polymeric systems. The photocatalytic mechanism in QD‐based membranes is predominantly regulated by light‐induced charge production and surface redox reactions. QDs composed of semiconductors and metal oxides, including TiO₂, ZnO, CdS, and their doped versions, can absorb ultraviolet or visible light, resulting in the excitation of electrons from the valence band to the conduction band. The resultant electron–hole pairs travel to the membrane surface, where they engage in oxidation and reduction processes with adsorbed water and oxygen molecules. These reactions produce extremely ROS, such as hydroxyl radicals and superoxide anions, which can decompose a broad spectrum of organic contaminants. When these QDs are fixed within or on the surface of polymer membranes, pollutant breakdown transpires immediately at the membrane interface, inhibiting the accumulation of foulants. Self‐cleaning behavior results from the ongoing or intermittent photocatalytic destruction of contaminants accumulated on the membrane surface. Under light irradiation, organic colors, proteins, oils, and biofilm‐forming bacteria can be mineralized or split into smaller, less sticky entities. This procedure reinstates membrane permeability without using external chemical cleaning agents. CQDs and GQDs augment this effect by enhancing membrane hydrophilicity and promoting uniform distribution of photocatalytic sites. The development of a hydration layer on the membrane surface diminishes initial foulant adhesion, while photocatalysis eradicates adsorbed pollutants, leading to synergistic antifouling and self‐cleaning efficacy. A further benefit of QD‐enabled photocatalytic membranes is their potential efficacy under visible light. In contrast to bulk photocatalysts that typically necessitate ultraviolet irradiation, QDs possess size‐dependent band gaps and adjustable surface states, enabling them to utilize visible light. Doping and surface functionalization enhance light absorption and optimize charge separation efficiency. This property is crucial for practical applications, enabling self‐cleaning membranes to function under sun irradiation or low‐energy indoor lighting, hence decreasing energy usage. In addition to fouling management, photocatalytic membranes can concurrently destroy trace organic pollutants, including pharmaceuticals, pesticides, and endocrine‐disrupting substances, during the filtration process. This dual filtration and degrading action improves treated water quality and minimizes the production of detrimental byproducts. Crucially, encapsulating QDs in polymer matrix reduces catalyst leaching and related toxicity issues, hence enhancing operational safety and stability.

The integration of photocatalysis with membrane technology presents a viable option to address the fouling issue. An IP PA NF membrane with self‐cleaning properties was synthesized through the integration of CQDs/titanium dioxide (CQD/TiO₂) nanoparticles [175]. The incorporation of hydrophilic CQD/TiO₂ nanoparticles enhanced membrane hydrophilicity and provided the NF membrane with a high water flux of 67.22 Lm⁻² h⁻¹, which is 1.8 times more than that of the pristine membrane, along with a sodium sulfate rejection rate of 96.7%. The produced NF membranes concurrently exhibited significant dye rejection rates of 99.1% for methyl blue (MB) and 99.8% for congo red. Furthermore, the photocatalytic capability of CQD/TiO₂, activated by visible light, enabled the membranes to effectively destroy MB dyes adhered to their surface. In sharp contrast to the outcomes of cyclic physical water purification, the flux recovery ratios were sustained at 97%–98% without compromising MB rejections during the cyclic fouling‐irradiation process, indicating consistent and effective self‐cleaning efficacy. Covalent triazine frameworks (CTFs), a subtype of covalent organic frameworks (COFs) derived from triazine units, exhibit a substantial specific surface area and superior optoelectronic characteristics, rendering them particularly appropriate for the fabrication of photocatalytic nanocomposites. A high‐performance photocatalytic self‐cleaning membrane was created by integrating WS2 quantum dot‐decorated CTF‐A (WS₂ QDS@CTF‐A) into a PVDF matrix in another study [176]. The composite membrane successfully combined the superior optoelectronic characteristics of CTF‐A with the robust photocatalytic efficacy of WS₂ QDs. In simulated sunshine, the membrane effectively produced •OH/•O^2– radicals, facilitating the breakdown of adsorbed dye molecules and imparting exceptional self‐cleaning and antifouling characteristics (Figure 12a). The improved membrane (QL2) demonstrated enhanced separation efficacy, with a pure water flux of 28.27 L·m^–2·h^–1·bar^–1 and a rejection rate of 99% for Eriochrome Black T. Saline wastewater and dye‐laden effluents represent common industrial wastewaters characterized by substantial discharge volumes, wherein elevated salt concentrations and intricate organic constituents aggravate fouling and complicate the permeability–selectivity challenge of traditional NF membranes. This study presents a unique magnetic‐field‐assisted IP method for the fabrication of photocatalytic thin‐film nanocomposite (M‐TFN) membranes, exhibiting improved antifouling and self‐cleaning capabilities. A multifunctional nanostructure, Fe3O4@CdS@CQDs, was produced using a one‐pot hydrothermal technique and incorporated into the aqueous phase of IP. In the presence of an external magnetic field, the nanoparticles were directed to the water–organic interface, resulting in the creation of a wrinkled PA surface characterized by enhanced roughness, hydrophilicity, and specific surface area [177]. In comparison to the traditional TFC membranes (6.1 L·m⁻²·h⁻¹·bar⁻¹, 98.2% Na₂SO₄ rejection) and TFN membranes (15.7 m⁻²·h⁻¹·bar⁻¹, 99.0% Na₂SO₄ rejection), the M‐TFN membranes demonstrated a markedly enhanced water flux of 22.5 m⁻²·h⁻¹·bar⁻¹ while achieving a high Na₂SO₄ rejection rate of 99.2%, thereby effectively addressing the permeability‐selectivity tradeoff (Figure 12b,c). The performance degradation of NF membranes due to concentration polarization (CP) and membrane fouling has significantly limited their practical application across several domains. Another study detailed the creation of an innovative interlayer between the substrate and the selective layer of traditional composite membranes by the coordinated manipulation of CQDs and PDA [178]. The strategy endows the membrane with dual functions simultaneously, in contrast to conventional strategies that address CP and fouling independently (Figure 12d). The incorporation of the PDA–CQDs layer modifies the IP process, thereby decreasing solute transport resistance and alleviating the CP issue. Secondly, the intercalated photoactive CQDs can decompose organic molecules adhered to the membrane surface when exposed to visible light, which is advantageous for economical fouling mitigation. A highly efficient photocatalytic membrane driven by visible light, comprising of Ag/CNQDs/g‐C₃N₄ and PVDF membranes, was successfully fabricated using vacuum filter crosslinking. This novel photocatalytic membrane exhibited superior photocatalytic degradation efficacy and self‐cleaning capabilities [179]. The Ag/CNQDs/g‐C₃N₄ photocatalyst with a coating quantity of 10 mg exhibited the maximum photocatalytic degradation of norfloxacin (NOR), with a quasifirst‐order kinetic constant (k) value of 0.0138 min⁻¹. Furthermore, the mechanism of the photocatalytic reaction was also examined (Figure 12e,f). Furthermore, BSA was utilized as the simulated pollutant to assess the self‐cleaning capability of the Ag/CNQDs/g‐C₃N₄‐PVDF composite membrane. Five types of amino acid‐functionalized graphene quantum dots (AA‐fGQDs) were synthesized and incorporated into the active layers of TFN membranes through the IP method to create self‐cleaning NF membranes with superior desalination efficacy [180]. The synthesized AA‐fGQDs and the resultant TFN NF membranes were methodically analyzed to examine the structural–performance correlations between the AA‐fGQDs and the NF membranes. The findings indicated that the desalination and photocatalytic self‐cleaning efficacy of the synthesized TFN membranes were intricately linked to the types and architectures of AA‐fGQDs (Figure 12g,h). The TFN membranes containing AA‐fGQDs with polar amino acids demonstrate superior desalination performance compared to those with non‐polar amino acids, thereby mitigating the tradeoff between water flux and salt rejection.

FIGURE 12.

(a) Photocatalytic self‐cleaning performance of QL2 membrane during nine cycles EBT filtration. Reproduced from reference [176]. Copyright (2025), with permission from American Chemical Society. (b) Performance of TFC, M‐TFN with Fe3O4@CdS, and M‐TFN with Fe3O4@CdS@CQDs membranes during five filtration–photocatalysis cycles under H₂O₂‐assisted conditions. (c) Performance comparison of the M‐TFN membrane with Fe3O4@CdS@CQDs under photocatalytic cycles with and without H₂O₂. Reproduced from reference [177]. Copyright (2025), with permission from Elsevier. (d) Preparation process of photocatalyst as interlayer for self‐cleaning nanofiltration (NF) membrane. Reproduced from reference [178]. Copyright (2019), with permission from American Chemical Society. (e) DMPO spin‐trapping ESR spectra and (f) quenching experiments of active species. Reproduced from reference [179]. Copyright (2022), with permission from Elsevier. (g) Schematic diagram of photocatalytic degradation of MB by GQDs/AA‐fGQDs and (h) normalized water flux, and MB rejection before and after photocatalysis. Reproduced from reference [180]. Copyright (2022), with permission from Elsevier.

7.5. Optical and Chemical Sensing Membranes

Optical and chemical sensing membranes have attracted growing attention as functional platforms for real‐time monitoring of environmental conditions, food quality, and biological processes. Integrating QDs into polymer membranes enables highly sensitive and selective sensing by combining the tunable photoluminescence, high quantum yield, and surface reactivity of QDs with the mechanical robustness and processability of polymers. As a result, QDs/polymer membranes offer versatile, flexible, and low‐cost sensing systems capable of transducing chemical or biological stimuli into measurable optical or electrical signals. Monitoring food pH is of critical importance, as it serves as a reliable indicator of freshness, ripeness, and overall quality during storage and distribution [181]. Beyond food systems, pH regulation is fundamental to maintaining acid–base balance in the human body, underscoring the need for rapid and accurate pH determination in applications ranging from food sterilization and fermentation to dietary management. Consequently, the development of responsive materials capable of tracking pH variations has become increasingly relevant for intelligent food packaging technologies. Hu et al. demonstrated that chitosan films incorporating CDs exhibited pronounced, pH‐dependent color transitions, shifting from yellow to pink as alkalinity increased, a characteristic change associated with fish spoilage [182]. This visually perceptible response enabled direct, real‐time assessment of fish freshness during storage and transportation. The enhanced sensitivity of the films was attributed to strong interfacial interactions between the CDs and the chitosan matrix, which amplified the optical response to subtle pH fluctuations, highlighting their promise for freshness‐indicating packaging applications. In a related approach, Ezati et al. functionalized CDs with resazurin to produce resazurin‐modified CDs (R‐CDs) via a hydrothermal route and integrated them into cellulose nanofiber (CNF) matrices to fabricate pH‐responsive indicator films [183, 184, 185]. The resulting CNF/R‐CDs films exhibited excellent UV‐shielding performance, blocking approximately 98.3% of UV‐B and 87.7% of UV‐A radiation [184]. Moreover, the films displayed rapid and reversible color changes from yellow to brownish‐red in response to alkaline environments and ammonia vapor (Figure 13a,b). The sensitivity of an R‐CD‐based indicator to pH variations as a gas sensor was examined by its capacity to alter color in reaction to ammonia and acid vapors (Figure 13c) [185]. Upon contact with ammonia vapor, the indicator became reddish‐brown. The indicator exhibited minimal color change upon exposure to acid gas, displaying a subtle, brilliant yellowish tint. The ammonium and hydroxyl ions in the indicator film undergo hydrolysis by water and distributed volatile ammonia, resulting in an alkaline indicative surface. When applied to shrimp packaging, the films showed clear visual responses correlated with pH variation and total volatile basic nitrogen (TVB‐N) levels, validating their suitability as intelligent freshness indicators (Figure 13d,e). Ding et al. developed starch/poly(vinyl alcohol) (PVA) films embedded with phosphorus‐doped carbon dots (P‐CDs) for real‐time monitoring of pork freshness [187]. As spoilage progressed, the accumulation of ammonia and other volatile nitrogenous compounds increased the local pH, triggering a fluorescence shift in the P‐CDs from blue to green. The starch/PVA matrix provided mechanical flexibility and ensured stable dispersion of P‐CDs, enabling efficient interaction with the surrounding atmosphere. This visual fluorescence response directly reflected meat spoilage dynamics, offering a practical tool for quality monitoring throughout storage and transportation. In another strategy, Kilic et al. cross‐linked citric acid‐derived CDs into gelatin films containing anthocyanins using ultraviolet irradiation [188]. The resulting films exhibited high sensitivity toward ammonia and were successfully integrated with a custom smartphone application (SmartFood) for real‐time and quantitative monitoring of chicken breast spoilage. Riahi et al. synthesized Ti‐doped CDs from sweet potato peels and titanium dioxide and incorporated them into anthocyanin/carrageenan films [186]. These films showed strong responsiveness to phosphate‐buffered saline across different pH values and to volatile ammonia indicators (Figure 13f,g), which further demonstrating the versatility of QD/polymer membranes in intelligent sensor systems.

FIGURE 13.

Visual response of the CNF/R‐CD3% pH‐sensitive indicator film under different conditions. Photographs of the CNF/R‐CD3% film after exposure to buffer solutions (a) with varying pH values, along with the corresponding colorimetric parameters (b). (c) Color changes and associated color values of the indicator film following exposure to acidic and ammonia vapors. (d) Application of the CNF/R‐CD3% indicator for real‐time monitoring of shrimp freshness at 25°C. (e) Schematic illustration of the pH‐ and ammonia‐responsive color transition mechanism of the indicator. Reproduced from reference [185]. Copyright (2023), with permission from Elsevier. Comparative color responses of (f) Carrageenan‐based sustainable active and pH‐dependent color‐changing composite films were fabricated by blending anthocyanin extracted from sweet potato peel (SPA)‐based and (g) carrageenan‐based (Car) indicator films across different pH environments, and (h) their visual transformations upon exposure to acetic acid and ammonia vapors. Reproduced from reference [186]. Copyright (2024), with permission from Elsevier.

7.6. Food Packaging and Smart Barrier Applications

Modern food packaging solutions must evolve from mere confinement to incorporate active and intelligent features that enhance shelf life, preserve food quality, and guarantee customer safety. In this context, polymer/QDs nanocomposite membranes have emerged as promising candidates for next‐generation food packaging and smart barrier applications due to their tunable physicochemical properties and multifunctionality. The incorporation of QDs into polymer matrices enables precise control over gas and moisture permeability, enhanced UV‐blocking capability, and improved mechanical and thermal stability, while simultaneously introducing active features such as antimicrobial, antioxidant, and sensing functions [189, 190]. The properties of polymer/QDs nanocomposite membranes position them as adaptable platforms for advanced food packaging systems that enable real‐time quality monitoring and safeguard against environmental and microbial degradation.

Food deterioration arising from inadequate preservation is governed by multiple factors beyond the intrinsic properties of the food matrix, with microbial proliferation and oxidative reactions representing the most critical challenges. Consequently, the development of food packaging systems with integrated antimicrobial and antioxidant functionalities is essential to suppress spoilage processes and reduce associated economic losses [191, 192]. Alongside polymers possessing inherent antibacterial properties, such as chitosan, a wide range of active agents have been explored as functional additives in advanced food packaging films. These include bio‐derived compounds (e.g., essential oils, polyphenols, and flavonoids) as well as nanostructured materials, such as QDs, metallic and metal oxide nanoparticles, and nanotubular systems [193, 194, 195]. Notably, recent years have witnessed a marked increase in research activity focused on the incorporation of QDs into active food packaging platforms.

Schmitz et al. reported the fabrication of Mg‐doped ZnO QDs (ZnO:Mg QDs) via a sol–gel approach and their subsequent incorporation into zein‐based films to produce nanocomposite food packaging materials [19]. Incorporation of a low filler content (0.83 wt%) markedly enhanced the antibacterial performance of pristine zein films, increasing inhibition efficiencies against Staphylococcus aureus and Escherichia coli from 0% and 3.2% to 19.5% and 8.1%, respectively. In addition to antimicrobial activity, the resulting composite films demonstrated improved surface hydrophobicity and superior ultraviolet shielding capability. In a related study, Priyadarshi et al. demonstrated sulfur as the precursor and embedded them into gelatin/agar blend films [196]. The SQD‐loaded films exhibited minimal cytotoxicity alongside notable enhancements in UV resistance, mechanical strength, and antioxidant activity (Figure 14a). Moreover, antimicrobial efficacy increased with SQD concentration; films containing 3 wt% SQDs achieved reductions of approximately 5 and 3 log₁₀ CFU mL⁻¹ against Listeria monocytogenes and E. coli, respectively, after 12 h of incubation, attributed to the intrinsic antimicrobial nature of the sulfur‐based QDs. Sul et al. developed CQDs via hydrothermal carbonization of waste banana peel and incorporated them into gelatin/chitosan composite films for beef preservation [202]. The resulting packaging materials exhibited pronounced antibacterial activity, yielding a 2 log₁₀ CFU mL⁻¹ reduction in E. coli within 3 h and complete inactivation of L. monocytogenes after 6 h of exposure. Similarly, Fu et al. prepared CQDs from chitosan precursors and blended them into chitosan/gelatin cast films, which displayed enlarged inhibition zones against E. coli and S. aureus and effectively suppressed microbial proliferation in fish during storage [203]. After 10 days, fish packaged with the CQD containing film showed a total bacterial count of 5.22 log₁₀ CFU g⁻¹, compared with 7.16 log₁₀CFU g⁻¹ for the control samples.

FIGURE 14.

(a) Fabrication of SQD‐embedded gelatin/agar composite films and the associated mechanisms underlying their antioxidant and antimicrobial functions. Reproduced from reference [196]. Copyright (2021), with permission from American Chemical Society. (b) Schematic representation of the preservation performance of CD‐modified gelatin/Persian gum films applied to trout fillets. Reproduced from reference [197]. Copyright (2023), with permission from Elsevier. (c) Illustration of the design of CD‐integrated chitosan films, highlighting their antimicrobial activity and effectiveness in extending the shelf life of pork. Reproduced from reference [198]. Copyright (2023), with permission from Elsevier. (d) Overview of the preparation of CD‐containing carboxymethyl cellulose coating films and their role in enhancing the storage stability of lemons. Reproduced from reference [199] Copyright (2022), with permission from Elsevier. (e) Schematic depiction of TPS preparation and the fabrication of CPCD‐integrated TPS/κ‐carrageenan composite films (top), along with digital photographs of the pristine film (TC0) and CPCD‐loaded hybrid films (TC1 and TC2). Reproduced from reference [200]. Copyright (2022), with permission from American Chemical Society. (f) Photographic comparison of banana storage under different conditions over time: without packaging (top), packaged with neat polypropylene (PP) film (middle), and packaged with PP film functionalized with NPSC‐dots (bottom), illustrating the enhanced preservation performance of the modified films. Reproduced from reference [201]. Copyright (2022), with permission from American Chemical Society.

More recently, Khoshkalampour, Ghorbani et al. synthesized CDs from grape leaves using a hydrothermal method and incorporated them into gelatin films cross‐linked with dialdehyde Persian gum [197]. The optimized composite film containing 30% CDs exhibited no detectable cytotoxicity, while demonstrating enhanced UV‐barrier performance and antibacterial activity against S. aureus and E. coli. As a result, the shelf life of trout fillets packaged with this material was extended from 4 to 8 days (Figure 14b). In a recent investigation, Wen et al. synthesized CDs from turmeric via a hydrothermal route and incorporated them into chitosan‐based films (Figure 14c) [198]. Upon irradiation with 405 nm light, the CDs‐modified chitosan films exhibited effective ROS generation, enabling photodynamic antimicrobial activity. Specifically, reductions of 3.19 and 2.05 log₁₀ CFU mL⁻¹ were achieved against Staphylococcus aureus and Escherichia coli, respectively, after 40 min of treatment. During pork storage, the CDs/chitosan packaging films delayed spoilage, preserved sensory attributes, and extended shelf life up to 10 days. Riahi et al. evaluated the applicability of CD‐based coatings for citrus preservation, focusing on fresh lemons (Figure 14d) [199]. In this study, CDs were produced from chitosan through a hydrothermal process and incorporated into carboxymethyl cellulose films. When applied as a surface coating with 5% CD loading, the formulation effectively suppressed mold growth and postponed quality deterioration, extending lemon shelf life from 7 to 21 days. Khan et al. reported the hydrothermal synthesis of CDs using garlic cloves as a carbon precursor, followed by their integration into sodium alginate/carrageenan composite films for active food packaging [204]. The inclusion of CDs substantially improved the films’ mechanical integrity, UV‐shielding performance, antibacterial efficacy, and antioxidant capacity. Notably, films containing 4 wt% CDs reduced E. coli and Listeria monocytogenes populations by 2.4 and 3.5 log₁₀ CFU mL⁻¹, respectively, after 12 h, demonstrating their effectiveness in beef preservation.

Beyond microbial contamination, oxidative degradation represents another dominant pathway of food quality loss, leading to nutrient depletion, off‐flavor formation, and the generation of potentially harmful aldehydic compounds [205]. Consequently, inhibiting oxidative reactions is critical for prolonging the shelf life of packaged foods, particularly lipid‐rich products such as meats, edible oils, nuts, and bakery items [206]. Compared with the direct incorporation of antioxidants into food matrices, antioxidant‐active packaging systems offer a strategy to reduce the reliance on chemical additives. In addition to plant‐derived bioactive compounds, various nanomaterials, including QDs, have been explored as antioxidant components in active packaging. Ezati and coworkers synthesized NCDs from glucose and urea and embedded them into CNF cast films [207]. The introduction of 1 wt% N‐CDs markedly enhanced the radical scavenging capacity of CNF films, increasing DPPH and ABTS scavenging efficiencies from 5.8% and 14.1% to 84.7% and 98.7%, respectively. These NCD‐containing films also exhibited superior antioxidant performance compared with undoped CDs and demonstrated effective antibacterial activity against L. monocytogenes, E. coli, and Aspergillus flavus. When applied as coatings, they extended the shelf life of strawberries and tangerines by more than 2 and 10 days, respectively. In a related work, sulfur‐doped CDs (S‐CDs) were prepared using turmeric and ammonium persulfate as carbon and sulfur sources, respectively [208]. Incorporation of 2 wt% S‐CDs significantly improved the antioxidant performance of pectin/gelatin composite films; however, their overall antioxidant efficiency was lower than that observed for undoped CD systems, likely due to hydroxyl radical generation. QD‐enabled packaging films and coatings have also demonstrated suitability for preserving lipid‐rich foods susceptible to oxidative degradation. For instance, Chen et al. incorporated banana peel‐derived CDs into gelatin/chitosan films, resulting in substantial increases in ABTS and DPPH radical scavenging activities from 20% and 10% to 99.4% and 74.5%, respectively [209]. The composite films effectively suppressed oxidative browning in stored beef, highlighting their potential for applications involving high‐fat or readily oxidizable food products. Consistently, Khan et al. observed concentration‐dependent enhancement in antioxidant performance for alginate/carrageenan films containing garlic‐derived CDs, with DPPH and ABTS scavenging efficiencies reaching 34.3% and 98.7%, respectively, at a CD loading of 4 wt% [204]. Importantly, these films delayed oxidative discoloration, odor development, and spoilage during beef storage.

UV radiation accelerates food degradation by promoting photo‐oxidation, nutrient loss, discoloration, and the formation of off‐flavors, thereby significantly shortening shelf life. Incorporating UV‐shielding functionality into food packaging is therefore essential, particularly for light‐sensitive and lipid‐rich products. In this context, QDs/polymer membrane‐based packaging systems are highly attractive, as QDs provide strong and tunable UV absorption while maintaining transparency in the visible range, enabling effective photoprotection without compromising package appearance. Uthirakumar et al. reported the fabrication of a PMMA‐based nanocomposite film incorporating uniformly dispersed CQD/N–ZnO nanoparticles [210]. The resulting film, with a thickness of approximately 250 μm, exhibited strong ultraviolet shielding performance, achieving UV attenuation efficiencies of about 85% under artificial UV irradiation and 92% under natural sunlight exposure. Wagh et al. reported the development of an advanced active and intelligent food packaging film composed of CNFs, anthocyanins extracted from Brassica oleracea, and carbon dots derived both from BO extracts and BO biowaste (BO‐CDs) [211]. Incorporation of 1.5 wt% BO‐CDs and 6 wt% BOA significantly enhanced the films’ physicochemical performance and ultraviolet shielding efficiency, yielding an improvement exceeding 189%. The BO‐CDs exhibited strong fluorescence emission, pronounced UV absorption, and effective antibacterial and antioxidant activities, with radical scavenging efficiencies of approximately 90% for ABTS and 80% for DPPH. Microscopic and spectroscopic characterizations confirmed uniform dispersion, elemental integrity, and interfacial compatibility of the functional components within the CNF‐based polymer matrix. Practical packaging evaluations demonstrated the films’ capability to monitor freshness in minced pork, fish, and shrimp through clear visual responses, thereby contributing to improved food quality management and shelf‐life extension.

In a related approach, heteroatom‐doped carbon dots were incorporated into flexible polymeric thin films using a simple physical blending strategy combined with a cast‐and‐peel fabrication method by Das et al. [200]. CDs reinforced thermoplastic starch (TPS)/κ‐carrageenan hybrid films were engineered to function as antioxidant packaging materials for extending the storage life of agricultural products (Figure 14e). These films exhibited high tensile strength (>40 MPa), optical transparency (∼77%), dimensional stability under high relative humidity (∼97%), and effective UV resistance. To assess food safety and preservation performance, time‐dependent CDs release behavior was examined in various food simulant media, revealing gradual changes in entrapment efficiency with increasing medium polarity. Kinetic analysis of the preplateau release profiles followed a non‐Fickian diffusion model. Notably, immobilization of CDs within the polymer network imparted excellent water vapor barrier performance, reduced moisture uptake, enhanced toughness, and good flexibility under mechanical deformation. Furthermore, the TPS/κ‐carrageenan/CDs composite films demonstrated strong antioxidant capacity, with DPPH and ABTS radical scavenging activities exceeding 85% and 90%, respectively, highlighting their potential as thin, durable, antioxidant, and moisture‐resistant alternatives for next‐generation food packaging applications. In a related work, Das et al. reported the synthesis of nitrogen‐, phosphorus, and sulfur‐codoped CDs (NPSCDs) via a one‐step hydrothermal route [201]. Owing to their strong radical scavenging capability, the antioxidant performance of the NPSCDs was systematically evaluated using multiple assays and practical demonstrations. Notably, the antioxidant functionality was successfully translated to polymer substrates by coating plastic films with NPSCDs. For the first time, NPSCDs were immobilized onto nonpolar polypropylene (PP) films through a photochemical covalent grafting strategy, enabling shelf‐life extension of stored food products without compromising the intrinsic properties of the polymer. Packaging bags fabricated from NPSCD‐coated PP films exhibited antifogging behavior and significantly reduced banana spoilage compared with pristine PP bags and unpackaged controls (Figure 14f). These findings highlight the effective antioxidant activity of NPSCD‐modified PP films and underscore their potential as low‐cost, fluorescent, and multifunctional plastic materials for next‐generation food packaging and storage applications.

7.7. Biomedical and Bioseparation Applications

The incorporation of QDs into polymer matrix platforms has created exciting opportunities in biomedical and bioseparation fields by integrating the inherent optical capabilities of QDs with the adjustable physicochemical characteristics of polymer matrices. QDs/polymer composite membranes provide a range of multifunctional capabilities, such as selective transport, fluorescence‐based sensing, and improved interaction with biological species. These features are essential for sophisticated biomolecule separations, targeted therapeutic delivery, and responsive biosensing systems. Bioactive GQDs based polymer composites exhibit strong affinity toward a wide range of biomolecules through π–π stacking and electrostatic interactions, enabling rapid and efficient loading of diverse therapeutic agents [212]. Similarly, their favorable membrane permeability and high biocompatibility facilitate enhanced intracellular drug delivery, thereby improving therapeutic efficacy, including against drug‐resistant cancer cells [213, 214]. Considerable efforts have therefore focused on exploiting bioactive GQD/polymer composites for in vivo drug delivery applications. Owing to their nanoscale dimensions, bioactive GQDs show reduced uptake by the reticuloendothelial system and diminished renal clearance, resulting in prolonged blood circulation times and improved delivery efficiency [215]. Sam et al. demonstrated pronounced anticancer activity using curcumin‐loaded graphene‐based nanocomposites under both in vitro and in vivo conditions. In their study, curcumin was incorporated into GO, double‐layer graphene oxide (DGO), and GQDs platforms via interactions with surface oxygen‐containing functional groups. These interactions played a decisive role in determining drug loading capacity, which was strongly pH dependent due to variations in surface functional group ionization. Among the tested systems, GQDs–curcumin nanocomposites exhibited the highest loading efficiency, reaching 40,800 mg g⁻¹, and showed superior anticancer performance compared with other curcumin‐loaded graphene derivatives at equivalent dosages. Notably, while curcumin and its GQDs composite were nonfluorescent in the bound state, fluorescence emission emerged following curcumin release, enabling GQDs to function simultaneously as drug carriers and fluorescent probes for tumor imaging [216]. Beyond drug delivery, bioactive GQD‐based polymer composites have been widely explored for biological imaging owing to their broad absorption profiles, narrow emission bandwidths, pronounced quantum confinement effects, and relatively high quantum yields combined with large molar extinction coefficients [217, 218]. Their ability to emit in the near‐infrared region further supports applications in deep‐tissue imaging, which is particularly relevant for early tumor detection, metastasis identification, and monitoring cancer reappearance [219]. For instance, Sheng et al. synthesized nitrogen‐doped GQDs (N‐GQDs) via a hydrothermal process using citric acid, poly(vinyl pyrrolidone), and glutamate as precursors, achieving a quantum yield of 64.2%. The resulting N‐GQDs functioned as effective fluorescent probes for chromium(VI) detection and cellular labeling of MCF‐7 breast cancer cells [220].

Nanoparticle‐ and QDs‐based bioprobes are increasingly recognized as alternatives to conventional small‐molecule probes for in vitro and in vivo bioimaging. However, their cellular uptake, intracellular trafficking, and cytotoxicity profiles differ markedly from those of molecular probes and are highly sensitive to surface chemistry. Tan et al. systematically investigated QDs with tunable surface charge, hydrophobicity, and polyethylene glycol (PEG) functionalization, revealing that surface ligands strongly govern cellular interactions, subcellular localization, and cytotoxic effects [221]. While all QDs exhibited dose‐dependent cellular uptake, cationic and hydrophobic QDs showed enhanced interactions compared with anionic counterparts. Positively charged QDs rapidly penetrated cells but induced higher cytotoxicity, whereas hydrophobic QDs primarily adhered to cell membranes without internalization. PEGylation effectively reduced nonspecific binding and cytotoxicity, although higher QD concentrations were required for cellular entry. These findings underscored the importance of balancing surface charge and hydrophobicity to engineer QD nanoprobes for controlled cellular labeling and targeted subcellular delivery. For particles in the 20–50 nm size range, cellular uptake and intracellular fate were predominantly dictated by surface chemistry, enabling precise control over biological behavior through rational ligand design.

In the context of tissue engineering and regenerative medicine, Gogoi et al. developed CDs decorated hydroxyapatite nanocomposites embedded within tannic acid and polyurethane matrices. Biological evaluations revealed excellent cytocompatibility, enhanced cell proliferation, and elevated alkaline phosphatase activity in MG‐63 osteoblast cells. The nanohybrids also displayed favorable mechanical performance, with tensile strength of approximately 20 MPa and elongation at break of 221%, alongside improved osteogenic potential [222]. Similarly, Lu et al. fabricated CD‐doped chitosan/nanohydroxyapatite (CS/nHA/CD) scaffolds via a freeze‐drying approach. These scaffolds upregulated genes associated with focal adhesion and osteogenesis, promoting enhanced cell attachment and osteoinductive behavior in rat bone mesenchymal stem cells. In vivo studies further demonstrated significantly increased formation of vascularized bone tissue within 4 weeks compared with CD‐free CS/nHA scaffolds [223]. Leveraging the intrinsic fluorescence and photothermal properties of CDs, the CS/nHA/CD scaffolds were additionally evaluated for near‐infrared (808 nm) photothermal therapy (PTT). Under NIR irradiation (1 W cm⁻²), the hybrid scaffolds exhibited efficient tumor cell ablation, effectively suppressing osteosarcoma proliferation in vitro and halting tumor progression in vivo.

Owing to their tunable electronic structure, particularly the ability to modulate the HOMO–LUMO energy gap, QDs are increasingly integrated with polymer matrices to engineer PNCs for advanced biosensing applications. CQDs, in particular, have emerged as versatile nanotransducers due to their strong photoluminescence, surface functionalizability, and compatibility with polymer hosts [224]. Jalili and Amjadi reported a molecularly imprinted biosensor in which PDA served as a recognition layer, green‐emitting CDs acted as the signal transducer, and 3‐nitrotyrosine (3‐NT) functioned as the template molecule. Following template removal, selective imprinted cavities were formed within the composite, enabling specific recognition of 3‐NT. The sensing mechanism relied on fluorescence quenching induced by target binding, mediated through hydrogen bonding and π–π interactions between CDs and PDA. Notably, the resulting sensor demonstrated superior sensitivity at the micromolar level, outperforming conventional HPLC and ELISA methods for 3‐NT detection in human serum samples [225]. In another notable contribution, Chowdhury et al. developed an electrochemical immunosensor for the ultrasensitive detection of hepatitis E virus (HEV) using nitrogen and sulfur codoped graphene quantum dots (N, S‐GQDs) integrated with gold nanoparticle‐embedded polyaniline nanowires (AuNP–PAni). Nitrogen incorporation significantly altered the electronic structure of the GQDs, leading to enhanced electrochemical activity, while the AuNP–PAni framework provided a large interfacial area that facilitated rapid electron transfer. This synergistic architecture enabled the reliable identification of HEV genotypes with an exceptionally low detection limit of 0.8 fg mL⁻¹ [226]. Polymer/QDs composites have also been explored for optical biosensing platforms. Jiang et al. fabricated a dual‐emissive biosensor film by homogeneously blending blue‐fluorescent polyurethane with green‐yellow emitting CQDs. The resulting composite exhibited high optical transparency (>85% above 550 nm), uniform CQD dispersion, and excellent mechanical robustness, including flexibility and ductility. Importantly, the temperature‐dependent and reversible fluorescence response of the CQDs endowed the material with potential for real‐time optical sensing applications [227].

Beyond sensing interfaces, polymer/QDs systems have been extensively investigated for bioimaging and diagnostic applications. Liu et al. reported a one‐pot synthesis of green‐emissive CDs using poly(acrylate sodium) (PAAS), which were subsequently functionalized with folic acid (FA) through hydrogen‐bond interactions to form a turn‐on fluorescence probe. The FA–CDs selectively targeted folate receptor–expressing cancer cells, enabling high‐contrast imaging in heterogeneous cellular environments. The excellent photostability and receptor‐specific activation of the probe highlight its promise for real‐time tumor visualization and fluorescence‐guided surgical interventions [228].

Stimuli‐responsive biosensing has further been realized using diselenide‐containing CDs (dsCDs) incorporated into ureidopyrimidinone‐functionalized gelatin (Gel‐UPy) hydrogels. These electrochemical wireless biosensors exhibited dynamic self‐healing, conductivity, and adhesion properties triggered by glutathione (GSH) or ROS. Cleavage of diselenide bonds modulated both the mechanical integrity and electrochemical output of the hydrogel, enabling effective in vivo cancer detection and responsive adhesion under oxidative microenvironments [229]. Targeted therapeutic sensing platforms have also been demonstrated. Shoval et al. engineered VEGF aptamer‐functionalized CDs capable of efficiently delivering anti‐VEGF agents across the cornea following topical administration. The intrinsic fluorescence of CDs enabled noninvasive monitoring of intraocular drug distribution, while in vitro and in vivo studies confirmed excellent biocompatibility and effective inhibition of VEGF‐induced angiogenesis [230]. In addition to diagnostic and therapeutic biosensors, QDs based PNCs have been translated into protective biomedical devices [167, 231]. Singh et al. reported the fabrication of CD–poly(vinylidene fluoride) (PVDF) nanoporous membranes for reusable, self‐sterilizing facemasks. These membranes combined a hydrophobic surface to suppress moisture accumulation with a dense nanoporous architecture capable of filtering particles larger than 100 nm while maintaining breathability. Upon brief exposure to solar irradiation, the embedded CDs absorbed visible light and converted it into thermal energy, enabling rapid self‐sterilization and highlighting the multifunctional potential of CD–PNC systems in personal protective equipment [232]. Collectively, these studies highlight the multifunctional potential of QD‐based polymer composites, not only for drug delivery, bioimaging, biosensors but also for photothermal cancer therapy and osteogenesis‐promoting bone repair platforms.

8. Environmental Impact of Polymer–QDs Nanocomposite Membranes

Polymer–QDs nanocomposite membranes have emerged as advanced materials offering enhanced separation performance, antifouling behavior, photocatalytic self‐cleaning, and antimicrobial activity. While these functionalities present clear technological advantages, the environmental implications of incorporating QDs into polymer matrices must be carefully evaluated across the full material life cycle, from synthesis to disposal. The environmental profile of nanocomposite membranes is significantly affected by the composition of QDs. Cadmium‐ and lead‐based semiconductor QDs have inherent toxicity hazards due to the possibility of metal ion leaching under operational or degradation conditions [143]. Even trace release can accumulate in aquatic ecosystems, affecting microorganisms and higher trophic levels [233]. Metal oxide QDs, such as TiO₂ and ZnO, are less toxic but may induce oxidative stress in nontarget organisms via ROS under light exposure [144, 234]. In contrast, CQDs offer lower toxicity and improved biocompatibility, though surface functionalization and particle size still influence bioavailability and ecological interactions [235, 236]. Therefore, compositional selection and surface engineering are crucial to minimizing environmental risks.

In addition to ecological considerations, potential human health implications must be carefully evaluated, particularly for membranes used in potable water treatment and biomedical interfaces. Chronic exposure to leached metal ions or nanoscale particles may induce cytotoxicity through oxidative stress, inflammatory responses, or cellular uptake and bioaccumulation [143, 237]. Occupational exposure during membrane fabrication, handling, or disposal also warrants attention, especially in large‐scale manufacturing settings [238]. Accordingly, standardized toxicological assessment including in vitro cytocompatibility studies, long‐term exposure analysis, and nanoparticle migration testing is essential to ensure compliance with emerging regulatory frameworks governing engineered nanomaterials. A major concern is the potential release of QDs during membrane operation. Fluctuating pH, ionic strength, oxidative agents, and mechanical stress can compromise nanoparticle/polymer interfaces, leading to leaching. Strategies such as covalent grafting, in situ QDs growth, core–shell architectures, and crosslinked polymer networks enhance retention stability [179]. Rigorous leaching studies under realistic operating conditions are essential to validate environmental safety and regulatory compliance prior to large‐scale application [239]. Such studies should encompass prolonged operational simulations, varying pH and ionic environments, and accelerated aging protocols to accurately predict long‐term nanoparticle stability and potential release profiles under practical conditions. QDs synthesis often involves high‐temperature reactions, organic solvents, and purified precursors, contributing to energy demand and environmental burden. Life cycle assessment (LCA) provides a framework to quantify these impacts and compare fabrication routes. Performance benefits, such as increased permeability reducing operational energy, and antifouling/self‐cleaning functions extending membrane lifetime, can offset upstream environmental costs. Incorporating both production metrics and operational efficiency is thus essential to assess net sustainability. End‐of‐life disposal of nanocomposite membranes poses additional challenges. Conventional incineration or landfilling may release nanoparticles or metals. Approaches to improve circularity include using recyclable thermoplastic polymers, biodegradable matrices combined with benign QDs, and encapsulating nanoparticles within stable inorganic shells to limit leaching. Standardized protocols for safe decommissioning and material recovery will be increasingly important as industrial adoption grows. Polymer–QDs nanocomposite membranes offer transformative potential in multifunctional separations. Addressing composition‐dependent toxicity, nanoparticle leaching, energy‐intensive synthesis, and end‐of‐life challenges is critical for sustainable development. Future research should focus on green synthesis, robust interfacial stabilization, long‐term leaching assessments, and comprehensive LCA to integrate high performance with environmental responsibility, enabling safe and industrially viable deployment.

9. Future Outlook and Commercialization Scopes

Scalability and manufacturing continue to be significant obstacles impeding the extensive use of polymer–QDs nanocomposite membranes, despite their encouraging performance in laboratory settings. A primary concern is the repeatability of QDs synthesis. QDs demonstrate traits that are contingent upon size, shape, and surface chemistry, with even little alterations in synthesis circumstances potentially resulting in substantial discrepancies between batches. In carbon‐ and graphene‐based QDs, parameters like precursor composition, reaction temperature, and post‐treatment significantly affect optical characteristics, surface functionality, and dispersibility. Semiconductor and metal oxide QDs present further hurdles owing to more stringent demands for stoichiometric control, crystallinity, and surface passivation. Inconsistent QD properties can directly result in variability in membrane permeability, selectivity, and long‐term stability, rendering repeatability a significant concern for industrial production. The expenses and scalability of fabrication techniques further hinder the shift from laboratory demonstrations to commercial production. Numerous high‐quality QDs are produced via solvothermal or hydrothermal processes that are economically challenging to scale, necessitate prolonged reaction durations, or utilize costly precursors and solvents. Semiconductor QDs frequently depend on high‐purity chemicals and intricate multistep surface modification procedures, hence elevating production expenses. Although carbon‐based QDs present a more economical option owing to the accessibility of inexpensive carbon sources and straightforward synthesis methods, issues concerning purification, yield enhancement, and waste management persist. Likewise, membrane production methods, including solution casting, phase inversion, and layer‐by‐layer assembly, must be modified to facilitate QD integration without jeopardizing throughput or cost‐effectiveness. Compatibility with roll‐to‐roll processing is an essential criterion for industrial membrane production. Roll‐to‐roll methods are extensively employed for the large‐scale production of polymer films and membranes, owing to their continuous operation and elevated productivity. Integrating QDs into these processes necessitates meticulous management of dispersion stability, ink or dope rheology, and coating uniformity. The aggregation of QDs during continuous processing can result in nonuniform membranes, defect accumulation, and variable performance. Moreover, it is essential to ensure ligand stability during shear forces, temperature fluctuations, and solvent evaporation to preserve interfacial integrity during high‐speed manufacture. The development of QDs solutions and the establishment of membrane casting processes suitable for roll‐to‐roll systems continue to be a prominent field of investigation.

In addition to fabrication issues, membrane fouling in actual operating settings constitutes a significant obstacle to scaling. Although most studies exhibit outstanding antifouling or self‐cleaning properties in controlled laboratory settings, actual feed streams are significantly more intricate. Industrial wastes, flue gases, and mixed gas streams possess variable compositions, particles, oils, and corrosive chemical species that can compromise designed membrane performance. Prolonged operation may result in fouling layers that obscure active QD sites, diminish photocatalytic effectiveness, or modify gas transport paths. Furthermore, recurrent cleaning cycles, mechanical stress, and chemical exposure might deteriorate the polymer–QDs interface, resulting in diminished performance or nanoparticle leaching. These concerns highlight the necessity for extensive pilot‐scale testing and durability evaluations in realistic situations.

Beyond fouling‐related degradation, prolonged exposure to harsh operational environments including extreme pH, oxidizing agents (e.g., chlorine‐based disinfectants), elevated temperatures, and high transmembrane pressures can induce polymer chain scission, interfacial debonding, and QDs surface oxidation. Repeated chemical cleaning cycles may further accelerate structural fatigue, alter QD surface passivation layers, and compromise nanoparticle immobilization, potentially leading to performance decline or increased leaching. In photocatalytically active systems, sustained irradiation may also trigger local polymer degradation due to ROS generation at the QDs–polymer interface. Therefore, systematic long‐term stability assessments including accelerated aging studies, cyclic filtration‐cleaning tests, and mechanical integrity analysis are essential to quantify durability under application relevant conditions. Establishing standardized durability metrics will be critical for comparing materials and advancing industrial qualification of QDs‐based membranes. The future advancement of polymer–QDs nanocomposite membranes is at a pivotal juncture, necessitating that ongoing material innovation aligns with production feasibility and market demands. Although laboratory‐scale investigations have effectively shown improved permeability, selectivity, antifouling properties, and multifunctionality, the subsequent phase of research will prioritize the translation of these benefits into durable, scalable membrane technologies. Future initiatives are anticipated to progress from proof‐of‐concept demonstrations to system‐level optimization, long‐term stability, and application‐specific performance metrics.

From a materials standpoint, the future prognosis significantly supports the utilization of environmentally friendly and economically viable QDs, especially carbon‐based and metal oxide QDs. These materials present diminished toxicity issues, compatibility with water processing, and enhanced regulatory approval relative to heavy‐metal semiconductor QDs. Improvements in green synthesis methods utilizing biomass‐derived precursors, solvent‐free techniques, and continuous‐flow reactors are expected to enhance batch‐to‐batch repeatability and output yield. Concurrently, systematic surface functionalization techniques will provide exact regulation of interfacial interactions, permitting the optimization of membrane characteristics for specific gas separation, water purification, or barrier functions.

Future research in membrane fabrication will focus on compatibility with industrial manufacturing methods, including roll‐to‐roll coating, slot‐die casting, and extrusion procedures. The incorporation of in situ QD growth or postfabrication surface immobilization techniques could mitigate aggregation problems and enhance scalability. Standardization of fabrication techniques and performance testing methods is essential for facilitating meaningful comparisons across studies and expediting technology transfer.

Despite rapid laboratory advances, universally accepted testing standards specifically tailored to QD‐based membranes remain limited. Variations in feed composition, operating pressure, temperature, membrane configuration, and reporting metrics hinder direct comparison of permeability, selectivity, antifouling efficiency, and photocatalytic performance across studies. Alignment with established membrane evaluation frameworks such as ASTM standards for water permeability and solute rejection testing (e.g., ASTM D6908), mechanical integrity assessments (ASTM D882), and chemical resistance protocols as well as ISO guidelines for membrane filtration performance (e.g., ISO 9906 for hydraulic performance evaluation) would provide a structured foundation for benchmarking. In addition, nanospecific considerations, including standardized nanoparticle leaching quantification, accelerated aging tests, and cyclic fouling‐cleaning protocols, should be integrated into these frameworks. The development of consistent durability and safety metrics will be pivotal for regulatory acceptance, reproducibility, and the commercialization of QD‐enabled membrane technologies.

The commercialization of polymer–QD nanocomposite membranes will probably use a phased strategy. In the short term, niche applications that can accommodate elevated material prices and leverage multifunctionality, such as high‐value gas separation, intelligent packaging, or self‐cleaning membranes for specialized water treatment, are anticipated to drive market penetration. These early adopters can function as pilot platforms to assess durability, safety, and economic viability under actual working settings. The mid‐term commercialization strategy will prioritize the optimization of the cost‐performance ratio, enhancement of membrane longevity, and the incorporation of QD‐based membranes into current modules and infrastructure without significant system modification. Long‐term commercialization will hinge on resolving regulatory, environmental, and lifecycle factors. Proving minimal nanoparticle leaching, the recyclability of membrane materials, and a low environmental impact will be essential for regulatory approval and public acceptability. Life‐cycle evaluation and techno‐economic analysis will have a progressively significant role in directing material selection and process optimization.

Although QD‐based membranes are largely at the research and pilot scale, several companies and industrial consortia are actively advancing related technologies that showcase pathways toward commercialization. For example, companies such as Quantum Solutions and Nanosys have established scalable production lines for semiconductor QDs, supplying materials for optoelectronic and sensing applications that directly overlap with emerging QDs‐functional membrane platforms. In the water treatment sector, organizations including Evoqua Water Technologies and Aquaporin A/S have initiated research partnerships investigating photocatalytic or antimicrobial nanomaterial enabled membranes, providing a translational pathway for QDs modified versions of these systems. Additionally, Dotz Nano has commercialized carbon based QDs for antifouling, tagging, and detection technologies that can be integrated into polymer membrane architectures for enhanced monitoring and self‐reporting functionality. Beyond water technologies, industries focused on gas separation and barrier coatings such as Air Products and Evonik are actively evaluating nanocomposite membrane formulations incorporating luminescent or catalytic nanomaterials, creating potential entry points for QDs enhanced designs. Collectively, these industrial activities illustrate the growing alignment between academic research on polymer–QDs nanocomposite membranes and real‐world technological adoption. Collaboration among academic researchers, membrane manufacturers, and end‐users will be crucial to synchronize research aims with industrial requirements and expedite scale‐up.

10. Conclusions

Polymer–QDs nanocomposite membranes represent a transformative materials platform capable of redefining the functional scope of conventional polymeric separation systems. Unlike traditional membranes that operate primarily as passive barriers, QDs integration enables the development of multifunctional architectures combining enhanced permeability–selectivity tradeoffs with antifouling, antimicrobial, photocatalytic, and sensing capabilities. The distinctive nanoscale dimensions, tunable surface chemistry, and interfacial activity of QDs allow precise modulation of polymer chain packing, free‐volume distribution, and transport pathways performance enhancements that are difficult to achieve using conventional inorganic fillers. A central conclusion of this review is that membrane performance is governed by the physicochemical characteristics of the incorporated QDs, including composition, size, surface functionality, and electronic structure. CQDs and GQDs offer advantages in terms of low toxicity, chemical stability, and compatibility with scalable processing, whereas semiconductor and metal oxide QDs provide photocatalytic activity and stimulus‐responsive functionality. However, the realization of these benefits is contingent upon robust interfacial engineering. Uniform dispersion, strong polymer–QD interactions, and long‐term interfacial stability are essential to prevent aggregation, suppress nanoparticle leaching, and ensure that QDs function as active nanocomponents rather than inert fillers. Despite substantial laboratory‐scale progress, key translational barriers remain. Reproducible QD synthesis, batch‐to‐batch consistency, scalable membrane fabrication, and durability under realistic operating conditions including complex fouling environments and chemical stress continue to limit industrial adoption. Addressing these challenges requires standardized synthetic protocols, process‐integrated fabrication strategies, and application‐driven performance benchmarking. Looking forward, the evolution of polymer–QDs nanocomposite membranes will be driven by three converging priorities. First, safe‐by‐design and sustainability‐oriented material selection including metal‐free or environmentally benign QDs and green synthesis strategies will be essential to meet regulatory and environmental expectations. Second, advanced interfacial engineering through tailored surface functionalization, in situ nanoparticle growth, and hierarchical structuring will enable membranes with programmable transport characteristics and stimulus‐responsive functionality. Third, integration of data‐driven materials discovery and multiscale modeling will accelerate rational optimization of structure–property–function relationships, minimizing empirical development cycles. Beyond incremental gains in separation efficiency, polymer‐QDs membranes are positioned to advance toward adaptive, multifunctional systems capable of concurrent separation, sensing, and self‐regeneration. In summary, polymer‐QDs nanocomposite membranes represent a high‐potential platform for next‐generation separation and barrier technologies. Their effective transition from laboratory discovery to industrial implementation will rely on the combination of materials reliability, scalable manufacture, sustainable development, and system‐level integration.

Author Contributions

Sayan Ganguly: conceptualization, literature review, visualization, writing – original draft, writing – review and editing. Poushali Das: conceptualization, literature review, formal analysis, writing – original draft, writing – review and editing. Tushar Kanti Das: formal analysis, literature review, writing ‐original draft, writing – review and editing.

Conflicts of Interest

The authors declare no conflicts of interest.

Biographies

Sayan Ganguly is a research associate at the University of Waterloo, Ontario, Canada. His research focuses on hydrogels, polymer nanocomposites, quantum dots, and advanced functional materials for diverse applications. He has authored over 80 peer‐reviewed research papers, edited several academic books, and contributed numerous book chapters in nanomaterials, polymers, and applied chemistry.

Poushali Das is a senior research scientist in the Faculty of Engineering at McMaster University, Canada. She previously held a postdoctoral position in the Department of Chemistry at Bar‐Ilan University, Israel, and earned her Ph.D. from the Indian Institute of Technology, Kharagpur, India. She is a recipient of several prestigious awards, including the DST INSPIRE Scholar Award (Government of India), the Horizon Europe Marie Skłodowska‐Curie Fellowship (European Commission), and the H.G. Thode Postdoctoral Fellowship (Canada). Das has authored over 70 research articles in leading international journals and has edited more than 10 books with CRC Press, Elsevier, and Springer. She serves as an associate editor for the Frontiers in Drug Delivery (Technological and Methodological Advances section) and has contributed as a topic editor and reviewer for several high‐impact journals. Her research focuses on multifunctional luminescent quantum dots, smart nanocomposites, and polymer‐based materials for sensing and biomedical applications.

Tushar Kanti Das is an assistant professor at the Institute of Physics, Silesian University of Technology, Poland. He earned his Ph.D. from Indian Institute of Technology, Kharagpur, India. focusing on polymer nanocomposites for catalytic applications. He was listed among the top 2% researchers worldwide for 2023–2024 and 2024–2025 (Scopus) and is a recipient of the DAAD Research Scholarship. He has published 62 research articles and 10 book chapters. He is associate editor of Frontiers in Materials and holds editorial roles while teaching. His research spans polymers, nanomaterials, quantum dots, catalysis, membranes, and water treatment focusing on sustainability.

Data Availability Statement

No data was used for the research described in the article.