Scalable and Systematical Conversions of Domestic Wastes to Core–Sheath Nanofibers for Photocatalytic Degradation of Antibiotics

Abstract

Batch nanofabrication of complex nanostructures remains a critical challenge, restricting their translation from laboratory design to industrial application. To address this, we report a conceptual and methodological advance by developing a brand-new “needle-confined region free-surface” triaxial electrospinning process. In a unique waste-to-resource concept, discarded polyethylene terephthalate (PET) beverage bottles were innovatively converted into the multifluid spinneret. This scalable device was utilized to batch-fabricate surface-porous core–sheath nanofibers using waste polystyrene (PS) foam as the primary matrix. These nanofibers comprised a porous PS/TiO₂ sheath to maximize catalytic exposure, while the polyacrylonitrile (PAN) core endowed the nanofibers with robust mechanical properties. As a proof of concept for this manufacturing approach, the resultant membranes were applied to antibiotic wastewater treatment, exhibiting excellent hydrophilicity, enhanced mechanical properties, and a high specific surface area with pronounced surface porosity. In a simulated tetracycline wastewater solution (pH 8), their photocatalytic degradation efficiency reached 70.05% within 2 h and was maintained at 66.74% after four reuse cycles. Beyond simply engineering a specific functional membrane, this integration of needle-based and free-surface electrospinning establishes a straightforward platform for the one-step scalable batch production of various multichamber nanostructures, providing robust support for advanced nanomaterials fabrication.

1. Introduction

Global freshwater resources are increasingly threatened by various contaminants. The widespread medical and agricultural use of antibiotics, such as tetracycline, leads to their accumulation in water bodies, fostering antibiotic-resistant bacteria and posing severe risks to human health. − Simultaneously, the rapid accumulation of plastic waste exerts tremendous pressure on environmental sustainability, contributing significantly to global “white pollution”. , To address these dual challenges, there is a pressing need to design sustainable systems that simultaneously accomplish plastic waste upcycling and effective antibiotic remediation. Photocatalytic technology utilizing TiO₂ offers a green solution for pollutant degradation. − However, the practical application of powdered photocatalysts is restricted by difficulties in recovery and recycling, necessitating a stable support material. In this context, the upcycling of waste plastics into high-value nanofibers has emerged as a transformative strategy to promote a circular economy. , Building on this concept, advanced photocatalytic membranes that immobilize active nanoparticles onto these flexible fibrous substrates have recently been extensively developed, exhibiting exceptional separability and robust performance in environmental remediation. , PS foam, widely available from discarded packaging, is an attractive polymer substrate for fabricating such functional materials. , Nevertheless, fibers derived solely from recycled PS inherently suffer from extreme brittleness and high hydrophobicity, which severely limit the mechanical durability and water permeability essential for wastewater treatment cycles. , To overcome these limitations, polyacrylonitrile, known for its outstanding mechanical robustness and favorable hydrophilicity, serves as an ideal reinforcement candidate. , Consequently, by integrating the photocatalytic activity of TiO₂, the chemical stability of waste PS, and the mechanical strength of PAN, a synergistic composite material can be engineered to effectively tackle these environmental issues.

Electrospinning is widely acclaimed as a versatile “top-down” technique for the single-step fabrication of nanofibers possessing high porosity and large specific surface areas. − However, monolithic nanofibers often struggle to achieve an optimal balance among physical properties, chemical properties, and functional performance. The core–sheath structure offers a solution to this dilemma. − It can be hypothesized that a PAN core serves as the mechanical skeleton, while a PS sheath loaded with TiO₂ particles performs the function of degrading pollutants. While standard coaxial and triaxial electrospinning provide platforms for creating such core–sheath structures, modified triaxial electrospinning has evolved to process combinations of spinnable and nonspinnable fluids, significantly expanding the applicability of material conversion. − Previous studies have demonstrated the utility of this approachsuch as manipulating solvent-evaporation rates with an outer nonspinnable solvent or utilizing multiple nonspinnable working fluidsto engineer complex nanostructures for controlled drug-release applications. − Building on these concepts, this study employs a modified triaxial electrospinning strategy utilizing a pure solvent as the outer fluid to fabricate nanofibers with a robust PAN core and a porous PS sheath. This strategy is expected to lubricate the spinneret nozzles, adjust jet solidification, and induce phase separation.

While electrospinning allows facile construction of complex nanostructures in laboratory settings, bridging the gap between intricate structural design and industrial-scale batch production remains a formidable challenge. , Throughout the development of electrospinning for nanofiber fabrication, fluid-guided electric-field methods have primarily been categorized into two types: needle-based electrospinning and free-surface electrospinning. − The former excels at regulating complex multichamber nanostructures (such as core–sheath or Janus) through precise capillary control, yet faces challenges in industrial-scale production because of low throughput. − The latter facilitates large-scale manufacturing but struggles to produce intricate multichamber structures in a controlled manner. , Although recent breakthroughs in scalable electrospinning have introduced various innovative high-throughput systemssuch as advanced free-surface setups and modified multineedle arrays to significantly boost productivitysuccessfully reconciling the trade-off between precise multichamber structural control and mass production remains largely unresolved. , Therefore, we integrated the traditional needle-type process with the concept of free surface electrospinning and termed this brand-new method “needle-confined region free surface electrospinning.” This technique retains the structural control capabilities of needle-based systems while possessing the potential for scalable batch fabrication of complex nanostructures. To achieve batch production of these complex core–sheath nanostructures, the equipment must incorporate a rationally designed spinneret, which is considered the core and the key innovation of the entire electrospinning system. , Guided by the concept of waste-to-resource, we conceptualized a novel triaxial spinneret made from waste PET beverage bottles. Its core innovation lies in the integration of metal capillaries with several “confined” free surface areas (i.e., holes) in a liquid reservoir formed by the bottle, which enables the scalable production of multichamber nanofibers. This design significantly compacts and simplifies the overall apparatus, providing strong support for the systematic treatment of different kinds of pollutants in a cost-effective manner.

In brief, this study utilized waste PS foam and PET beverage bottles as raw materials to fabricate, via a custom-built triaxial electrospinning system, a porous core–sheath nanofibrous membrane in a batch process. Evaluated against the “12 principles of green membrane materials and processes,” this strategy exemplifies a sustainable waste-to-resource approach by integrating waste minimization with process intensification. The resultant nanofibers were systematically characterized in terms of morphology, internal structure, physical state, component compatibility, mechanical performance, hydrophilicity, and antibiotic degradation capability. This strategy achieves the dual goals of scalable production and environmental restoration.

2. Materials and Methods

2.1. Materials

The waste polystyrene foam boxes were cleaned and cut into small pieces. The beverage bottles used to manufacture new spinnerets were cleaned and set aside for subsequent use. PAN (M _w = 85,000) and rutile titanium dioxide (TiO₂, P25, ≥99.8%, 5–10 nm) were purchased from Sigma-Aldrich (Shanghai, China). Dimethylformamide (DMF, 99.8%) and anhydrous ethanol, purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China), were used in this study. Tetracycline hydrochloride (≥98%) was purchased from Shanghai Macklin Biochemical Technology Co., Ltd. (Shanghai, China). All solvents were used as received without further purification. Deionized water was produced by a laboratory water purification system.

2.2. Preparation of Nanofibers

A 30% (w/v) base solution, designated as F1 for solid nanofibers, was prepared by dissolving 30 g of washed waste polystyrene in 100 mL of DMF. The F2 solution was subsequently obtained by dispersing 2 g of nanotitanium dioxide into this base solution. For the F3 and F4 core–sheath nanofibers, the core fluid was a 10% (w/v) PAN solution prepared by dissolving 10 g of PAN in 100 mL of DMF. The sheath fluid was a dilute, nonspinnable 10% (w/v) PS solution (10 g of PS in 100 mL of DMF) doped with nano-TiO₂ particles: 2 g for F3 and 5 g for F4. Additionally, pure DMF was used as the outer fluid to facilitate the fabrication of all nanofiber types.

The experiment setup comprised a high-voltage generator (ZGF60 kV/2 mA, Wuhan, China), three syringe pumps (two KDS100 and one KDS200, Cole-Parmer, USA) for delivering the working fluid, a homemade beverage bottle spinneret, and a flat plate collector covered with aluminum foil. During electrospinning, the high-voltage power supply was set to 25.4 kV. The collection distance was 17 cm. The core flow rate was 18 mL/h, and the sheath flow rate was 12 mL/h. The temperature and relative humidity were 18 ± 2 °C and 40 ± 5%, respectively. Four types of nanofibers were prepared, and the flow rates of each fluid are listed in Table .

1. Parameters about the Preparations of Various Electrospun Nanofibers.

		Working Fluid (Flow rate, mL/h)
No.	Electro-spinning	Inner	Middle	Outer	Structure
F1	Modified coaxial	30% PS (30)	-	DMF (3)	Monolithic
F2		30% PS + 2% TiO2 (30)	-	DMF (3)	Monolithic
F3	Modified triaxial	10% PAN (18)	10% PS + 2% TiO2 (12)	DMF (3)	Core–sheath
F4		10% PAN (18)	10% PS + 5% TiO2 (12)	DMF (3)	Core–sheath

2.3. Characterization of Raw Materials and Nanofibers

The molecular weight of the waste PS foam was determined by gel permeation chromatography (GPC). The morphology and various physical and chemical properties of the nanofiber membranes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), mechanical property tests, and water contact angle tests. The porosity was characterized by an ethanol immersion method. Detailed characterization data are provided in the Supporting Information.

2.4. Photocatalytic Activity

A 20 mg/L tetracycline hydrochloride (TCH) solution with pH 8 was prepared as simulated wastewater, and 30 mg of nanofiber membrane was immersed therein. Prior to photodegradation, a 60 min dark adsorption experiment was conducted first, and the absorbance of the solution was measured every 10 min. Photocatalytic degradation was carried out under a 35 W full-wavelength xenon lamp; absorbance was measured every 20 min over 120 min. TCH absorbance at 357 nm was measured using the Lambda 750UV spectrometer (PerkinElmer, USA), and its concentration was then calculated using the standard formula

$$D=\frac{c_0-c_t}{c_0}\times 100\%$$ 1

where D is the degradation rate, C ₀ the initial concentration, and C _t the concentration at time t.

The photocatalytic cycle test was repeated after the nanofiber film was washed, dried, and irradiated for 2 h.

2.5. Statistical Analysis

The mean ± standard deviation (SD) is used to display all data. To evaluate significant differences between groups, one-way analysis of variance (ANOVA) was employed. Where ANOVA indicated significance (p < 0.05), Dunnett’s post hoc test was applied to identify specific differences.

3. Results and Discussion

3.1. Batch Production through Modified Triaxial Electrospinning

Modified triaxial electrospinning fundamentally requires at least one spinnable fluid to be rheologically dominant, thereby drawing nonspinnable components into continuous fibers. , The waste PS foam collected in this study originates from diverse sources, exhibiting broad molecular-weight distributions and variable compositions. Moreover, the PS solution tended to premature solidification during electrospinning. To mitigate these challenges and achieve the desired surface porosity, we employed a modified triaxial electrospinning strategy. A spinnable PAN solution constituted the structural core to ensure continuous jet formation. The middle layer comprised a dilute, functional PS/TiO₂ suspension that, although intrinsically nonspinnable, was successfully drawn into a sheath layer by the core layer. Crucially, pure DMF was used as the outer working fluid. This outer solvent layer serves two purposes: (i) it establishes a localized solvent-rich atmosphere that retards premature jet solidification and prevents PS adhesion to the capillary wall, thereby avoiding nozzle clogginga common issue when electrospinning naturally derived macromolecules. − (ii) It modulates the solvent evaporation rate to induce thermodynamic instability and phase separation, the primary mechanism for producing surface porosity. ,

To bridge the gap between laboratory-scale structural design and industrial production, this study developed a novel “needle-confined region free-surface” system to improve the traditional electrospinning setups. The conventional multineedle or needleless technologies often fail to strike a balance between structural precision and high output. To resolve this issue, we propose a new electrospinning technique based on a homemade beverage-bottle spinneret featuring a “needle-in-hole” design. This spinneret is expected to combine the advantages of both needle-based and free surface electrospinning. The complete electrospinning system is illustrated in Figure . Monolithic fibers were prepared from a polymer-based working fluid. For core–sheath fibers, the core comprised a spinnable polymer solution, the middle layer a dilute nonspinnable polymer solution, and the outermost layer pure solvent.

1.

Batch production through a modified triaxial electrospinning.

As shown in Figure a, the batch spinneret was fabricated by cutting and assembling two PET beverage bottles into a large-capacity container. The structural details are shown in Figure b,c. Delivery of the electrospinning solutions occurs in two parts. First, the core and middle-layer fluids were supplied through five long metal needles that passed through the beverage bottle and terminated in a concentric configuration. These capillary tubes converge into two collective inlet ports at the top (Figure (b2,b3)). At the bottle bottom, the needles were scattered into five outlets (Figure c). Second, the outer layer fluid was fed through sidewall ports in the beverage-bottle body (Figure (b1)). This fluid exits via the bottle’s bottom aperture, creating a “confined” liquid surface that envelops the metal capillaries without introducing capillary forces. The main components of the batch electrospinning system include a high-voltage power supply, a homemade beverage bottle spinneret, three syringe pumps, and a fiber collector (Figure e). The beverage bottle spinneret was fixed by an insulated Teflon rod (Figure f). High voltage was applied to the working fluids via an alligator clip connected to the spinneret. When a suitable high voltage is reached, five compound Taylor cones formed simultaneously at the spinneret outlets (Figure g). Figure h shows the typical processes of electrospinning, including the formation of a Taylor cone, a straight fluid jet, and a bending and whipping unstable region. Furthermore, the chemical compatibility between the PET spinneret and DMF was tested (FTIR spectra are shown in Supporting Information Figure S1), revealing a stable chemical structure without any detectable ester hydrolysis. Consequently, the PET spinneret demonstrates excellent chemical durability, ensuring its long-term viability in DMF-based electrospinning.

2.

Batch PET spinneret and batch electrospinning setup. (a–c) Fabrication and construction of the beverage-bottle-based spinneret: (a) assembly process; (b) overall appearance and a bare metal section that delivers high voltage; (b1–b3) three top liquid inlets; (c,c1–c5) five bottom triaxial outlets and their enlarged view. (d–h) Electrospinning apparatus and operational process: (d) syringe connections; (e) system overview; (f) voltage application; (g) simultaneous formation of five Taylor cones; and (h,h1–h5) visualization of stable jets and bending and whipping regions.

The batch production of core–sheath nanofibers exhibited excellent robustness and continuity. The whole homemade apparatus and the experimental conditions are shown in Video SI. Under intense illumination, the simultaneous five working processes from the five bottom concentric outlets are exhibited in Video SII. Like a conventional single-spinneret process, they had the typical Taylor cones, straight fluid jets, and the instable regions, which displayed an illusion of continuous divisions due to the limited shooting frequency per minute (16 shots/min, Huawei P20 smartphone). When a better Canon (G7X, Canon Co. Ltd., Tokyo, Japan) was exploited to capture the phenomenon with a magnification of 16×, the real bending and whipping processes containing gradually enlarged loops are disclosed in Figure (h1–h5).

For comparison, a whole coaxial process using a concentric spinneret for preparing the core–sheath nanofibers and their optical microscopic images are shown in Figures S2 and S3, respectively, in the Supporting Information. To keep the process going, semisolid deposits had to be manually removed from the spinneret nozzle. The new electrospinning processes not only can be implemented for a continuous batch production but also are free from the above-mentioned negative phenomena. This advantage stems from (i) the outer hole acting as a confined free surface that exerts no adverse capillary forces on Taylor cone formation; (ii) the bottle is composed of PET (its FTIR spectra are shown in Figure S4 of the Supporting Information), which provides fewer opportunities for the possible clinging of viscous fluid and the emergence of semisolid substances around the fluid jets; (iii) the lubrication effect of the outer solvent DMF.

A combined cost and process efficiency assessment was conducted for the batch electrospinning. By substituting virgin PS pellets, which commercially cost approximately USD 1.5–3.0/kg, with waste PS foam, the raw material expenditure is effectively reduced to near zero. In terms of production efficiency, the theoretical production of solid nanofibers is calculated according to the following formula

$$Y=V_t\times \frac{(V_{\mathrm{i}}\times W_{\mathrm{i}})+(V_{\mathrm{m}}\times W_{{\mathrm{m}}_1})+(V_{\mathrm{m}}\times W_{{\mathrm{m}}_2})}{V_{\mathrm{i}}+V_{\mathrm{m}}+V_{\mathrm{o}}}\times 100\%$$ 2

where V _i, V _m, and V _o represent the flow rates of the inner, middle, and outer layers, respectively; V _t is the sum of these flow rates; W denotes the concentration of each solid component; and W _i, W _m1 , and W _m2 denote the concentrations of PAN, PS, and TiO₂, respectively. Given that the outer layer is composed of solvent, no solid content is contributed by this layer.

The batch electrospinning pumped 33 mL of working fluids per hour, theoretically yielding 33 × (18 × 10% + 12 × 10% + 12 × 5%)/(18 + 12 + 3) × 100% ≈ 3.6 g of solid nanofibers. The conventional single-needle system pumped 3.3 mL of working fluids per hour (core, middle, and sheath flow rates of 1.8, 1.2, and 0.3 mL/h), theoretically yielding 0.36 g of solid nanofibers. The results indicate that the productivity of the batch electrospinning used in this study was 10 times that of the conventional single-needle electrospinning. Based on the formula for electric power consumption

$$P=U\times I$$ 3

where P is the electrical power; U is the applied voltage; and I is the generated current.

The total electrical energy P consumed for operating an electrospinning system includes the electrical energy P _b (typically around 30–50 W) for driving the high-voltage power supply and the syringe pump, as well as the electrical energy P _j required for driving the working fluid. In our study, although the applied voltage is as high as 25.4 kV, the spinning current is merely on the microampere scale. Thus, the energy required to drive working jets is negligible, making P _t overwhelmingly dominated by P _b. Consequently, the batch electrospinning system enables a 10-fold or greater expansion in production capacity with only a marginal increase in overall power consumption.

We combined the traditional needle-type electrospinning with the concept of needleless liquid surface electrospinning to form a combined electrospinning system featuring a coworking of “needle” and “confined liquid surface”. Importantly, this batch electrospinning retains the structural precision of needle-based methods, paving a new way for the batch production of complex architectures, including core–sheath, Janus, and sophisticated multichamber nanostructures. − As a proof-of-concept, this integrated platform overcomes traditional production bottlenecks and provides a cost-effective, energy-efficient pathway for the industrial-scale deployment of advanced functional nanomaterials.

3.2. Morphology and Structure

Figure a–d show the diameter distributions and SEM images of nanofibers. The prepared fibers all have a columnar morphology, and no bead-like or spindle-like morphology is observed. SEM images of the batch-produced F4 electrospun fibers collected from various positions are shown in Figure S5 of the Supporting Information. A 30% (w/v) polystyrene solution was selected at 30% (w/v) for monolithic fiber preparation. Due to variations in processing, additives, molecular weight, and the wide molecular weight distribution of the waste PS, it is hard to determine a certain electrospinnable PS concentration. To prevent excessive parameter fluctuations between different products that could lead to suboptimal fiber morphology, after exploring the spinnable window of a batch of PS foam at a range of 20–40%, a middle concentration was chosen as the control group to prepare monolithic nanofibers. At the same time, the molecular weight (M _w) of the waste PS foam used in this study was characterized by gel permeation chromatography (GPC), which was approximately 24.46 × 10⁴ g/mol (Figure S6 in the Supporting Information). F1 exhibited microscale diameters, whereas F2, after nano-TiO₂ incorporation, showed a higher diameter distributionaccompanied by the observation of minor TiO₂ particle agglomeration within the fibers (Figure b). In contrast, F3 and F4 had average diameters of 468 and 475 nm, respectively (Figure c,d). Despite the same total fluid flow rate of 30 mL/h, core–sheath nanofibers are significantly thinner than monolithic PS fibers. This is primarily attributed to (i) the core spinnable PAN solution playing its key role during the electrical drawing of working fluids under the electrical fields; (ii) the outer solvent and also the dilute middle fluid of PS extending the tensile time of the core–sheath fluid jets during the bending and whipping processes; and (iii) the smaller concentration of PS in the nonspinnable middle fluids.

3.

(a–d) SEM images and corresponding diameter distributions of F1–F4; (e,f) TEM images of F4 and F3; and (g) EDS mapping of F4.

Further investigation of the nanofibrous structural characteristics using TEM, as shown in Figure e,f, reveals that F4 exhibits a clear core–sheath structure, with significant grayscale contrast between the center and the sides of the nanofibers. At the same time, irregular porous structures are also observed on the fiber surfaces, as reflected by the presence of many small regions with a smaller grayscale. As indicated in Figure e, TiO₂ nanoparticles were observed to be homogeneously distributed on the sheath PS layers of F4. However, when F3 was collected at the edge of the deposition regions on the collector, the TiO₂ nanoparticles were observed to be occasionally absent (Figure f).

The generation of surface pores is primarily driven by NIPS. Although the high boiling point of DMF typically favors the formation of dense fibers, its high hygroscopicity plays a decisive role here. The outermost DMF layer retards jet solidification, providing an extended flight time that allows the jet to actively absorb water vapor from the humid atmosphere (40 ± 5%). This influx of moisture triggers thermodynamic instability, leading to a liquid–liquid phase separation into polymer-rich and polymer-poor phases. Combined with the low concentration of the sheath polymer, this process ensures the formation of a well-defined porous morphology upon the final evaporation of the solvent/nonsolvent mixture. , Therefore, the porosity is attributed to moisture-triggered NIPS facilitated by the unique fluid dynamics of the modified triaxial electrospinning. The EDS mapping (Figure g) confirms the presence of C, N, O, and Ti elements in F4, revealing that the agglomerated particles observed at specific locations are TiO₂. Overall, with the help of modified triaxial electrospinning, porous-surfaced core–sheath nanofibers with finer diameters are robustly and continuously produced.

3.3. Physical Condition and Compatibility

The physical condition of the nanofibrous membranes was described using XRD patterns (Figure a). The figure shows distinct characteristic peaks for PAN, with a primary peak at 16.8° and a secondary peak at 29.5°. Waste PS exhibits a broad diffraction peak around 19°, indicating its amorphous physical state. The typical diffraction peaks at 25.3°, 37.8°, 48.0°, and 54.2° were assigned, respectively, to the (101), (004), (200), and (105) facets of anatase TiO₂. The diffraction peak at 25.3° confirms the anatase structure of TiO₂, which corresponds well with the JCPDS file (card no. 21-1272). F2 also displayed TiO₂ peaks, albeit with reduced intensity owing to decreased crystallinity upon embedding. F3 and F4 appeared in an amorphous state with attenuated TiO₂ peaks, attributable to (i) the reduction in TiO₂ crystallinity after being supported on PS and (ii) the coating effect of the polymer.

4.

(a) XRD patterns; (b) FTIR spectra; and (c) chemical formulas of PS and PAN.

Using infrared spectroscopy, the compatibility of the polymer and functional particles was examined (Figure b). The absorption bands located at 2245 cm^–1 and 1450 cm^–1 are assigned to the CN (cyano) stretching and C–H bending modes of the PAN structure, respectively. The peaks of PS molecules at 3059, 3026, and 2922 cm^–1 are attributed to the stretching vibrations of C–H bonds, and the peaks observed at 1600, 1492, and 1452 cm^–1 are due to the stretching vibrations of CC bonds. The vibration peaks of these groups are related to the molecular structure of PAN and PS (Figure c). Additionally, the F2 exhibits the characteristic functional groups of PS, and an anatase Ti–O–Ti bending vibration peak is observed around 470 cm^–1, indicating the loading of TiO₂ nanoparticles. These characteristic functional groups are also observed in the F3 and F4, confirming the successful fabrication of core–sheath nanostructures.

3.4. XPS Analysis

The valence states and content of the components in the F4 were examined using XPS. According to Figure a, the fibers contain C, O, N, and Ti elements, consistent with the EDS analysis results (Figure g). Peaks in the C 1s spectrum (Figure b) appear at 285.55, 284.80, and 283.74 eV, corresponding to CN in PAN, CC, and Ti–C bonds, respectively. The N 1s peak appears at 397.20 eV (Figure c). In the O 1s XPS spectrum (Figure d), the peaks at 529.46 and 531.36 eV are attributed to the Ti–O bond and hydroxyl group (OH), respectively, and the CO bond at 533.39 eV is speculated to be derived from the additives in the PS foam raw material. The characteristic peaks at 462.97 and 457.49 eV in Figure e correspond to the 2p_1/2 and 2p_3/2 spin–orbitals of Ti in TiO₂, indicating the presence of Ti⁴⁺.

5.

XPS spectra of F4: (a) survey spectrum; (b) C 1s; (c) N 1s; (d) O 1s; and (e) Ti 2p. Mechanical properties: (f) stress–strain curves of F1–F4.

3.5. Mechanical Properties

The mechanical properties of the modified membranes for water pollution treatment are crucial for their practical applications. Sufficient strength maintains active component functionality during degradation and withstands repeated washing cycles. As shown in Figure f, F1 exhibited stresses below 0.1 MPa with pronounced fluctuations, including a decrease followed by an increase. Such behavior stems from the low density and stiffness of PS, which result in a loose structure with less physical cross-linking between the fibers when electrospun into nanofibers. During stretching, the membrane tends to separate, causing individual fibers to break first. Nano-TiO₂ in F2 improved the interaction between polymer chains, reduced interchain slippage, and marginally increased tensile strength. In contrast, the stresses of F3 and F4 reached 1.35 and 1.60 MPa, respectively, and exhibited higher elongation and better mechanical properties. This improvement stems from the PAN core, which significantly reinforced the membrane.

3.6. Hydrophilic Properties

Figure shows the changes in water contact angles on the fiber membranes. Fiber membranes used for water treatment typically need to be hydrophilic. Hydrophilicity improves water permeability, antibiotic adsorption, membrane–pollutant contact (enhancing degradation), and antifouling resistance. , As shown in Figure a,b, after 180 s, the water contact angles of the F1 and F2 decreased by only 1.46° and 1.41°, respectively, indicating the high hydrophobicity of the polystyrene-based monolithic fiber membranes. Compared to F1, F2 showed a 4.44° decrease in the initial contact angle, which is ascribed to the integration of nano-TiO₂ particles that effectively improved the membrane’s hydrophilicity. This enhancement occurs for two main reasons: first, TiO₂ itself is inherently hydrophilic; second, the addition of TiO₂ increases the roughness of the fibers, further contributing to the reduction in contact angle. , In contrast, F3 and F4 exhibited dramatic decreases (Figure c,d). The water contact angle of the F3 dropped from 55.63° to 24.11° in just 5 s, while the F4 dropped from 57.99° to 17.40°. These values indicate complete hydrophilicity. This transformation stems from the synergistic effect of the porous core–sheath architecture. Specifically, the porous PS sheath allows water to penetrate through pores and contact the hydrophilic PAN core. Furthermore, surface-exposed TiO₂ aggregates and increased geometric roughness further facilitate the rapid spreading of water droplets, leading to the observed hydrophilicity. Notably, the relatively large standard deviations observed for F3 and F4 at 0 s are attributed to this rapid dynamic wetting process. The instant the water droplet contacts these highly hydrophilic surfaces, it undergoes significant kinetic jittering, causing the test system’s CCD camera to capture slightly different transient states across parallel measurements.

6.

Water contact angles: (a) F1; (b) F2; (c) F3; and (d) F4.

3.7. Evaluation of Photocatalytic Activity and Reusability

First, the P1 was introduced as a comparison to assess the impact of the porous structure of F4. P1 comprised 10% (w/v) PAN as the core layer and 10% PAN with 5% TiO₂ loaded as the sheath layer (its characterization data are shown in Figure S7 of the Supporting Information). Before the photodegradation experiment, a 60 min light-shielded adsorption experiment was conducted first. The results shown in Figure S8 of the Supporting Information indicated that adsorption was negligible (<1.5%) for all membranes.

Figure a presents the first cycle TCH degradation curves for F1, F2, F3, F4, and P1. F2, F3, and F4 achieved 65.84%, 68.26%, and 70.05% within 2 h, respectively, versus 67.8% for P1. Figure f illustrates the porosities measured by the ethanol immersion method, which were 82.21% for F4 and 70.87% for P1. This evidence substantiates that the surface-porous architecture of F4 successfully exposes a greater density of catalytic sites, thereby leading to a superior degradation efficiency. Additionally, despite having a lower sheath flow rate and TiO₂ content compared to those of F2, F3, and F4 demonstrated superior photocatalytic performance. This enhancement is primarily ascribed to the sheath thin layer distributions of TiO₂ nanoparticles and fine hydrophilicity. The F1 reached a degradation rate of 19.96% after 80 min, after which it leveled off. Although no photocatalyst was added to F1, some degradation still occurred. This is likely due to (i) the slight degradation of the alkaline TCH solution under light in the experimental conditions and (ii) the presence of unknown catalytic components in the industrial-grade PS foam.

7.

(a) Photodegradation curves of TCH using F1–F4 and P1. Four-cycle reusability tests for (b) F2, (c) F3 (d) F4, and (e) P1. (f) Porosity of F4 and P1. SEM images of (g) F2, (h) F3, and (i) F4 after four cycles of water treatment.

The durability and reusability of nanofibrous membranes are essential for their practical use. , Figure b–e shows four-cycle degradation curves for F2, F3, F4, and P1. Due to its highly hydrophobic nature, the F2 achieved an average degradation rate of only 64.8% in the first two cycles. After two cycles, the membrane was damaged and fragmented, thoroughly mixing into the TCH solution, which led to an increased degradation rate of 73.23% in the third cycle. As the membrane continued to be lost, the photocatalytic degradation rate of the F2 decreased in subsequent cycles, and the lost membrane fragments entered the water, causing secondary pollution. In contrast, the F3, F4, and P1 showed degradation rates of 68.26%, 70.05%, and 67.80% in the first cycle and 65.39%, 66.74%, and 63.40% in the fourth cycle, with only slight losses observed. This indicates that the composite nanofiber membrane possesses good mechanical strength and maintains stability during the photocatalytic degradation of TCH, making it suitable for repeated use without causing secondary pollution to the water. Meanwhile, F4 offered more active sites than P1, yielding higher degradation. The SEM micrographs in Figure g–i visualize the state of F2, F3, and F4 after four cycles of use, respectively. F2 was extensively fractured, whereas F3 and F4 merely became disordered without breakage.

3.8. Photocatalytic Mechanism Analysis

Electrospinning converts waste PS foam into porous core–sheath membranes that photodegrade water pollutants, as illustrated in Figure . When nano TiO₂ absorbs energy greater than its bandgap, it generates electron–hole pairs that subsequently transport to the catalytic surface. These charge carriers then react with water or hydroxide ions (OH^–) to form hydroxyl radicals (^•OH), or with O₂ to form superoxide radicals (^•O₂ ^–). , These radicals can degrade pollutants, as shown by the following equations

$${\mathbb{e}}^{-}+{\mathrm{O}}_2\to {}^{·}{{\mathrm{O}}_2}^{-}$$ 4

$${\mathrm{h}}^{+}+{\mathrm{H}}_2\mathrm{O}/{\mathrm{O}\mathrm{H}}^{-}\to {}^{·}\mathrm{O}\mathrm{H}+{\mathrm{H}}^{+}$$ 5

8.

Mechanism diagram of photodegradation of water pollutants by porous core–sheath nanofibers derived from waste PS.

In this work, on one hand, the combination of TiO₂ with electrospun fibers exhibits a synergistic effect in the degradation of TCH. The high specific surface area characteristic of its porous structure plays a significant role in enhancing the degradation of pollutants. Additionally, PAN cores further improve hydrophilicity and mechanical integrity, facilitating water-treatment applications and recycling. On the other hand, core–sheath nanostructure is one of the most popular multichamber configurations, which can be exploited for conceiving many routes for “turning waste into treasure” through the advanced material conversion methods, particularly those capable of creating nanoproducts in a batch manner. ,

While the physical manufacturing and functional feasibility of the “needle-in-hole” batch production strategy have been successfully validated, several limitations remain that warrant further investigation. As a proof-of-concept study centered on a waste-to-resource methodology, the current antibiotic degradation experiments were primarily employed as a comparative tool to demonstrate structural advantages. Consequently, future work is required to utilize TOC and LCMS/HPLC to trace degradation intermediates and confirm mineralization safety, alongside EPR for the direct detection of active species. Furthermore, BET surface area quantification and DMA interfacial assessment will be conducted to further optimize the material’s structural and mechanical robustness for practical wastewater environments. These advanced characterizations will be the primary focus of our next research phase to mature this technology for practical, large-scale remediation applications.

3.9. Environmental Applicability and Sustainability Analysis

Modern membrane fabrication is increasingly evaluated against the “12 principles of green membrane materials and processes.” These principles provide a rigorous framework focusing on waste minimization, process intensification, and the utilization of sustainable raw materials. The environmental applicability and sustainability of the batch electrospinning were evaluated against the “12 principles of green membrane materials and processes” (Figure ).

9.

Interconnectivity of the 12 principles of green membrane materials and the 12 principles of green membrane processes. PAT = process analytical technology; AI = artificial intelligence. Reproduced with permission from ref . Copyright 2024 The Royal Society of Chemistry.

Regarding material selection, our study directly aligns with Principle 2.1 (consider greener compounds) and Principle 2.12 (cradle-to-grave mindset). By upcycling nonbiodegradable domestic wastesPS foam and PET beverage bottlesinto membrane polymer matrix and core spinneret components, this research reroutes plastic waste from landfills back into the value chain. This waste-to-resource approach minimizes the dependency on virgin petroleum-based polymers and addresses the global “white pollution” challenge. Furthermore, the integration of a PAN core fulfills Principle 2.10 (design for robust performance) by endowing the membrane with the mechanical integrity required for multiple reuse cycles, thereby extending its operational lifespan. While the current use of DMF represents a shortfall under Principle 2.1­(consider greener compounds), its use was necessary at this study. In future research, we are committed to exploring biobased or greener alternatives to further align with this principle.

Regarding the fabrication process, the modified triaxial electrospinning aligns with Principle 2.6 (reduce complexity and steps) and Principle 3.1 (minimize processing steps) by enabling the one-step fabrication of surface-porous core–sheath nanofibers. From an engineering perspective, the “needle-in-hole” design fulfills Principle 2.11 (design for scalability) and Principle 3.6 (minimize the footprint). The compact spinneret achieves high-throughput production while occupying a minimal space compared to bulky industrial multineedle arrays. Furthermore, the batch electrospinning significantly enhances mass productivity with only a marginal increase in total power consumption, aligning with Principle 3.4 (minimize energy consumption). In summary, this synergy between waste upcycling and process intensification establishes a sustainable pathway for scalable environmental remediation.

4. Conclusions

By integrating waste beverage bottles into the spinneret design, a novel and scalable modified triaxial electrospinning process was established to successfully transform domestic waste into functional surface-porous core–sheath nanofibrous membranes for antibiotic wastewater remediation. This approach exemplifies a highly adaptable manufacturing strategy for the batch fabrication of complex nanoscale structures. The core–sheath nanofiber membrane, featuring a waste PS-TiO₂ sheath and a PAN core, exhibited a TCH degradation efficiency of 70.05% within 2 h under simulated conditions (pH 8) while maintaining a value of 66.74% after four repeated uses. Specifically, the core–sheath design addressed the inherent limitations of recycled plastics: the PAN core endowed the membrane with essential mechanical robustness and superhydrophilicity to support repeated water treatment cycles, while the waste PS-based sheath engineered with a porous surface via phase separation maximized the specific surface area and exposure of TiO₂ active sites for the efficient generation of reactive radicals.

Beyond functional performance, this research offers significant implications for scalable nanotechnology by utilizing a “needle-in-hole” design that organically integrates needle-based precision with free-surface throughput. By ensuring stable Taylor cone evolution at a confined interface and circumventing negative capillary forces, this technology enables the scalable batch production of complex nanostructures, effectively overcoming the inherent throughput limitations traditionally associated with high-precision electrospinning. Furthermore, this waste-to-resource strategy minimizes costs, including raw materials, core spinnerets, and operational energy consumption. This significantly reduces the economic barriers faced in large-scale industrial production.

This research highlights the dual environmental benefits of upcycling solid plastic waste and decontaminating antibiotic-polluted water, providing a sustainable, scalable, and efficient technology for enhancing the regional environmental quality and ecological safety. While current investigations focus on laboratory-scale validation, future work will involve optimizing fluid distribution uniformity and evaluating the long-term operational stability to gradually mature this technology.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.6c03877.

• Supplementary Video 1: Apparatus & parameters (MP4)

• Supplementary Video 2: Working processes (MP4)

• Details on the characterization of raw materials and nanofibrous membranes; FTIR spectra of PET before and after soaking in DMF; a typical traditional coaxial electrospinning process and its resulting nanofibers; FTIR spectra of the PET waste bottle; supplementary SEM images of the batch electrospinning; molecular weight distribution curve of the waste PS; preparation and characterization of the control P1 nanofibrous membrane; and physical adsorption experimental data (PDF)

§.

R.D. and Y.R. contributed equally to this work. Ran Dong: writingoriginal draft, methodology, investigation, formal analysis, writingreview and editing, conceptualization, software, and data curation. Yingao Ru: methodology, investigation, data curation, formal analysis, and methodology. Xinyi Zhang: formal analysis and investigation. Jiaqi Zhu: resources, software, and methodology. Haifeng Wen: conceptualization, methodology, supervision, and resources. Daihua He: methodology, supervision, resources, software, validation, and visualization. Deng-Guang Yu: conceptualization, funding acquisition, supervision, and writingreview and editing.

The authors declare no competing financial interest.