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. 2026 Sep 18;11(38):57408–57421. doi: 10.1021/acsomega.6c05761

Phosphorus-Doped Cellulose-Derived Carbon Aerogel for Synergistic Adsorption of Congo Red and Cu(II) from Complex Wastewater

Kangle Zhao †, Junbin Wu †, Jing Guo †, Zhenwei Wu †, Beili Lu †, Biao Huang †, Guanfeng Lin †,‡,*, Jianhua Lv †,*
PMCID: PMC13628609  PMID: 42824559

Abstract

Wastewater produced by dye-related industries commonly contains metal ions, together with organic dyes. Their simultaneous removal is difficult because these pollutants differ in charge, molecular size, and binding behavior. To treat wastewater cocontaminated with copper ions (Cu­(II)) and Congo red (CR), phosphorus-doped carbon aerogel (PCA) was fabricated from sodium carboxymethyl cellulose by sol–gel processing, freeze-drying, and one-step carbonization, with phytic acid serving as the phosphorus source and activator. In the single-component systems, Cu­(II) and CR are retained by PCA through combined electrostatic attraction, surface complexation, hydrogen-bond formation, and enrichment within the hierarchical pore structure, giving maximum adsorption capacities of 76.40 and 641.86 mg g–1, respectively. The adsorption kinetics follows the pseudo-second-order model, and the equilibrium data are better described by the Langmuir isotherm model. In the Cu­(II)–CR binary system, PCA exhibits synergistic adsorption toward both pollutants with CR showing a more pronounced enhancement. The maximum adsorption capacities increase to 87.83 mg g–1 for Cu­(II) and 1795.32 mg g–1 for CR, representing 1.15- and 2.8-fold increases, respectively. This synergy is mainly attributed to Cu­(II)-mediated local charge regulation and interfacial interactions, which reduce the electrostatic repulsion toward CR and promote its adsorption on the PCA. Regeneration and simulated wastewater experiments further support the applicability of PCA for treating cocontaminated wastewater. This study provides new insights into the design of carbon-based adsorbents for the synergistic removal of heavy metal ions and organic dyes from complex wastewater systems.

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1. Introduction

Wastewater containing both heavy metal ions and organic dyes is increasingly generated during industrial development, creating a persistent challenge for wastewater treatment. Congo red (CR), a widely used synthetic dye, is a common contaminant in industrial wastewater. This dye poses a serious environmental challenge because of its biotoxicity and poor biodegradability. In addition to organic dyes, heavy metal ions in industrial wastewater, particularly copper ions (Cu­(II)), not only cause environmental pollution but also pose potential risks to human health. Thus, effective treatment techniques are urgently needed to reduce the impact of these contaminants on the environment and human health. Currently, various technologies, such as adsorption, membrane separation, electrochemical treatment, and photocatalytic degradation, are used to treat dyes and metal ions in wastewater. Among them, adsorption has attracted attention because of its simple operation, good removal efficiency, low energy consumption, and wide application scope. Nevertheless, the majority of current studies focus on the removal of heavy metals or organic dyes in isolation, while little attention has been given to the concurrent removal of both pollutants from complex wastewaters. The reason for this is that these two types of pollutants exhibit significant differences in size and physicochemical properties, which tend to compete for the same active sites on adsorbents, resulting in a competitive adsorption effect. Therefore, in wastewater containing multiple pollutants, the simultaneous removal of dyes and metal ions has become a formidable challenge, and the development of high-performance adsorbents with abundant adsorption sites to remove complex contaminants efficiently has become crucial.

Sodium carboxymethyl cellulose (CMC) is a widely available, low-cost, and renewable cellulose derivative with good water solubility. Its molecular chains contain abundant hydroxyl and carboxymethyl groups, which enable the formation of stable gel networks through cross-linking interactions. Therefore, CMC can serve as an important precursor for constructing carbon aerogel adsorbents. Owing to these structural advantages, CMC-based aerogels and their derived carbon materials have recently been explored for the design and fabrication of water-treatment materials. For example, Wang et al. prepared sodium carboxymethyl cellulose-derived carbon aerogels by pyrolyzing cross-linked CMC xerogels. During carbonization, the cross-linked gel network was converted into an interconnected porous carbon skeleton, endowing the material with both hydrophilicity and light absorption capability for solar-driven water purification. This finding suggests that constructing a precursor gel network is an effective strategy for regulating the pore structure and application performance of CMC-derived carbon aerogels. Jing et al. fabricated a CMC-based functional aerogel using CMC, sodium styrenesulfonate, and acrylic acid through a one-pot method. By introducing sulfonic and carboxyl groups into the CMC network, the resulting material exhibited a three-dimensional porous structure and abundant surface-active sites, enabling its use for selective adsorption of cationic dyes and dynamic wastewater treatment. These studies indicate that the pore structure and surface chemistry of CMC-based materials can be effectively regulated through gel-network construction, carbonization, and surface functionalization, thereby improving their performance in water-treatment applications. In addition, heteroatom doping is an effective modification strategy for further enriching the surface functional groups of carbon materials. The incorporation of heteroatoms such as N, O, P, S, and B into carbon frameworks can regulate the electronic structure, surface polarity, and defect density of carbon materials while introducing additional active sites, thereby strengthening the interactions between adsorbents and pollutants. Among these heteroatoms, phosphorus has a relatively low electronegativity and a large covalent radius. After being incorporated into the carbon framework, P atoms can form stable C–P bonds with neighboring carbon atoms and introduce phosphorus-containing functional groups such as PO, P–O, and C–P–O, which provide additional interaction sites for the adsorption of heavy metal ions and dye molecules. Tegin et al. prepared phosphorus-doped hydrochar from pistachio shell waste through hydrothermal carbonization followed by H3PO4 surface modification and applied it to Cu­(II) adsorption. Their results showed that H3PO4 modification enhanced the Cu2+ adsorption capacity of the material. Sudarsan et al. prepared activated carbon from Spathodea campanulata flowers using orthophosphoric acid activation and employed it for CR removal. The phosphoric-acid-activated carbon exhibited favorable surface adsorption ability, which was beneficial for CR immobilization. These studies demonstrate that phosphorus sources or phosphoric acid-based activators can regulate the surface chemistry of carbon materials and increase the number of active sites involved in pollutant binding, thereby improving their adsorption performance toward heavy metal ions and dye molecules.

Inspired by these studies, phytic acid was selected in this work as both the phosphorus source and activator for CMC-derived carbon aerogels. Phytic acid contains abundant phosphate groups, which can introduce P-containing functional groups such as PO and P–O into the carbon framework during carbonization. Meanwhile, it can also function as an activating and structure-regulating agent, contributing to improvements in pore structure, hydrophilicity, and surface reactivity. , Therefore, incorporating phytic acid into the CMC-derived carbon aerogel system is expected to achieve the synergistic regulation of pore architecture and O/P-containing active sites, thereby enhancing the adsorption capacity toward Cu­(II) and CR. Based on the above considerations, PCA was prepared in this study using CMC as the carbon source and phytic acid as both the phosphorus source and activator through sol–gel processing, freeze-drying, and high-temperature carbonization. The prepared PCA was applied to the adsorption of Cu­(II) and CR in both single-component and binary systems. The adsorption performance, environmental adaptability, and cycling stability of PCA were systematically investigated. In addition, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and zeta-potential analyses were employed to elucidate the adsorption mechanisms. Particular attention was given to the synergistic adsorption behavior and interfacial interactions in the Cu­(II)–CR binary system. This work provides new insights into the design of CMC-derived carbon aerogels for treating complex wastewater containing both heavy metal ions and organic dyes.

2. Experimental Section

2.1. Experimental Materials

For details of the experimental ingredients, see the Supporting Information (Text S1).

2.2. Material Characterization

For details on material characteristics, see the Supporting Information (Text S2).

2.3. Fabrication of PCA

In a water bath at 80 °C, 2 g of CMC was slowly added into 50 mL of deionized water with constant stirring to accelerate the dissolution, and then 6 g of phytic acid solution was slowly dripped into the mixture to form a hydrogel, which was then transferred to a petri dish to set and freeze-dried to form an aerogel, and then finally placed in a muffle furnace protected by nitrogen and heated up to 900 °C at 10 °C min–1 and then held for 1 h. Then, the solution was cooled to chamber temperature. After cooling, it was washed to achieve neutrality and dried at 100 °C to obtain PCA (see Figure for the synthesis schematic). Meanwhile, phytate-free samples were prepared under the same process conditions as control sample and named CA.

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PCA synthesis schematic.

2.4. Adsorption Experiments

For details on adsorption experiments, see the Supporting Information (Text S3).

2.5. Modeling Analysis

To clarify the adsorption interactions in the single-component systems, the experimental data were analyzed using four kinetic models, two isotherm models, and thermodynamic parameters (Table S1). In the binary system, to quantitatively analyze the interaction between Cu­(II) and CR, we employed the adsorption capacity ratio (R q) as an evaluation metric.

2.6. Regeneration of PCA

To evaluate the reusability of PCA in single-component systems, separate adsorption–desorption cycling experiments were conducted for CR and Cu­(II). Briefly, 0.01 g of PCA was added to 100 mL of CR solution (80 mg L–1) or Cu­(II) solution (20 mg L–1) and shaken until adsorption saturation was reached. The CR-loaded PCA was regenerated by using 0.1 M NaOH, whereas the Cu­(II)-loaded PCA was regenerated by using 1 M HCl. Finally, it was rinsed to a neutral pH using deionized water and then dried. The regeneration performance of PCA was evaluated in five consecutive adsorption–desorption cycles.

2.7. Assessment of the Adsorption Capacity of PCA in Real Aqueous Environment

Three water samples, tap water, lake water, and river water (from Fuzhou, China), were employed as solvents. These solvents were used to prepare CR (80 mg L–1, pH = 5.0) and Cu­(II) (20 mg L–1, PH = 6.0) solutions for simulating the application of PCA in real aqueous environments.

3. Results and Discussion

3.1. Characterization of PCA and CA

The morphology and microstructure of the CA and PCA were examined by SEM. CA exhibits a relatively smooth surface with abundant pores (Figure a,b), whereas PCA shows a denser structure composed of tightly arranged nanoparticles (Figure d,e). This difference may arise from the cross-linking between CMC and phytic acid, which forms a more compact carbon skeleton. EDS mapping and elemental analysis show (Figure c,f and Table S2) that PCA mainly contains C, O, Na, and P, whereas the P content detected in CA is extremely low, at just 0.04%; in contrast, the P content in PCA is nearly 10 times that in CA, indicating that P doping was successfully realized in PCA. Additionally, PCA contains more O atoms than CA, which indicates that PCA has more surface-active sites that are closely related to chemisorption.

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SEM and EDS elemental maps of CA (a–c) and PCA (d–f).

Contact angles of CA and PCA were measured to assess hydrophilicity changes after P incorporation. As depicted in Figure S1, the contact angle of CA is 127.5°, whereas that of PCA is 45.0°, indicating that PCA has superior hydrophilicity. This improvement may be related to P-induced surface charge redistribution and the increased abundance of polar O/P-containing functional groups on PCA, and good hydrophilicity is favorable for reducing diffusion resistance at the adsorbent–solution interface, thereby enhancing the adsorption performance.

The crystalline structure and defect degree of CA and PCA were studied by XRD and Raman spectroscopy. The peaks observed at 2θ values of approximately 23 and 43° (Figure a) are attributed to the (002) and (100) diffraction planes of graphitic carbon, respectively. For the (002) diffraction peak, the diffraction peak of PCA is flatter than that of CA, which suggests that PCA has a more disordered structure and that P doping increases the degree of defects. Figure b displays two broad bands at 1350 and 1585 cm–1, both of which are characteristic of carbonaceous structures. The former corresponds to disordered carbon (D), while the latter is ascribed to graphitic carbon (G). On this basis, variations in the I D/I G ratio can be used to reflect changes in the defect density and graphitic ordering of carbonaceous materials. PCA shows a higher I D/I G value than CA (1.05 vs 1.03), indicating that P incorporation introduced additional structural defects and weakened graphitic ordering, consistent with the XRD results.

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XRD patterns (a), Raman spectra (b), N2 adsorption–desorption isotherms (c), and pore-size distributions (d) of CA and PCA; FTIR spectra (e), XPS survey spectra (f), and high-resolution XPS spectra of C 1s (g), P 2p (h), and O 1s (i) of CA, PCA, and adsorption-treated PCA samples.

N2 adsorption–desorption was conducted on CA and PCA in order to ascertain their respective pore structures and pore-size distributions. The adsorption–desorption isotherms for both CA and PCA exhibit the characteristic type IV behavior, associated with H3-type hysteresis loops (Figure c). This pattern indicates that hierarchical porosity is formed, encompassing both micropores and mesopores, as a result of the thermal treatment process, which agreed with the pore-size profile results (Figure d). PCA possessed a larger specific surface area and greater total, mesopore, and micropore volumes than CA (Table S3). This phenomenon is owing to the dual functions of phytic acid. In addition to serving as a phosphorus source, phytic acid acts as an acid modulator and structure-directing agent, promoting the formation of additional mesopores and micropores during carbonization. The micropores provide adsorption space, whereas the mesopores act as transport channels that facilitate the diffusion of contaminant molecules into the material’s interior, and thus PCA has a greater ability to remove contaminants than CA.

The surface functional groups of CA and PCA were analyzed with FTIR spectra (Figure e). Both CA and PCA show absorption bands at 3438, 2919, 2853, 1627, 1397, 1095, and 797 cm–1, indicating the presence of similar carbon-based functional groups. The peaks at 3438 and 1397 cm–1 are regarded as hydroxyl vibrations, while the peak at 1095 cm–1 corresponds to the symmetric C–O bond stretching vibration. Concurrently, spectral peaks at 2919, 2853, and 797 cm–1 are attributed to C–H stretching vibrations. The characteristic peak at 1627 cm–1 corresponds to stretching vibration of the CC bond in the aryl group or the CO bond in the carboxylic acid group. Compared with CA, PCA exhibits an additional peak at 1173 cm–1, which is assigned to the stretching vibrations of P–O and PO bonds in bridged (P–O–P) and terminal (POOH) phosphorus structures, confirming the effective doping of PCA with P. The introduction of phosphorus-based functional groups into adsorbent materials can effectively enhance their chemical adsorption capacity for metal ions and organic pollutants.

The surface chemical compositions of CA and PCA were further examined by XPS. In the survey spectrum (Figure f), distinct P 2s and P 2p signals appeared in PCA, and the calculated P content reaches 3.82% (Table S4), suggesting that phytic acid introduces phosphorus species into the carbon framework during carbonization. The chemical environments of C, P, and O in PCA were further examined using the high-resolution XPS spectra in Figure g–i. The C 1s spectrum is deconvoluted into five peaks at 284.5, 284.9, 285.5, 286.4, and 289.2 eV, corresponding to C–C, C–OH, C–P, CO, and C–O–P. The P 2p spectrum contains three fitted peaks at 132.9, 133.8, and 134.8 eV, corresponding to C–PO, C–P–O, and C–O–P species. In the O 1s spectrum, the peaks at 533.92, 532.87, 531.46, and 532.12 eV are related to C–O, P–O, PO, and C–O–P groups, respectively. Together, the XPS analysis verifies P incorporation into the carbon framework and reveals abundant O/P-containing functional groups on PCA, offering potential binding sites for Cu­(II) and CR adsorption.

3.2. Effect of Solution pH

Solution pH strongly affects the surface properties of adsorbents by altering the charge distribution and the protonation/deprotonation behavior of functional groups. Therefore, examining the zero-charge point (pHpzc) can help to study the electrostatic adsorption mechanism further. The surface charge properties of CA and PCA were evaluated by determining their pHpzc values. The pHpzc values (Figure a) of CA and PCA are 6.50 and 5.27, respectively, indicating that phosphorus doping shifts the surface charge transition of the carbon aerogel to a lower pH. For PCA, the surface is mainly protonated and positively charged when the solution pH is below 5.27, whereas deprotonation occurs at pH values above 5.27, leading to a negatively charged surface. This pH-dependent surface charge behavior is expected to strongly influence the electrostatic interactions between the PCA and ionic pollutants. The pH ranges selected for the Cu­(II) and CR solutions were 3–7 and 5–9, respectively, since metal ions are easily precipitated under alkaline conditions, and CR undergoes an obvious color change when the pH value is below.

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Effect of pHpzc values of CA and PCA (a); effect of solution pH on the adsorption capacity of Cu­(II) (b) and CR (c).

As shown in Figure b, Cu­(II) adsorption on PCA increases as the solution pH rises and then stabilizes at pH 6.0. Under acidic conditions, abundant H+ ions compete with Cu­(II) for the available adsorption sites, thereby suppressing Cu­(II) adsorption. In addition, the protonated PCA surface is unfavorable for the electrostatic attraction of positively charged Cu­(II). At elevated pH, O/P-bearing surface groups on PCA tend to lose protons, thereby increasing the negative charge density of the adsorbent surface. This enhances the electrostatic attraction between PCA and Cu­(II) and also facilitates the coordination of Cu­(II) with surface functional groups such as −OH, CO, PO, and P–O. Thus, Cu­(II) uptake is favored as the pH increases, but the solution pH was maintained at 6.0 to prevent Cu­(II) hydroxide precipitation under more alkaline conditions.

For CR, the uptake capacity declines as the solution pH increases and then gradually levels off (Figure c), mainly because the adsorption of anionic CR is closely associated with the pH-regulated surface charge of PCA. At pH 5.0, the PCA surface is close to its pHpzc and contains more protonated adsorption sites, which favor the electrostatic attraction between the positively charged sites and anionic CR molecules. With increasing pH, deprotonation of the PCA surface becomes more pronounced, leading to a more negatively charged surface and a stronger electrostatic repulsion toward CR anions. In addition, excess OH– ions can occupy available adsorption sites, thereby further inhibiting CR adsorption in alkaline media. These pH-dependent trends confirm that electrostatic attraction contributes substantially to the uptake of both Cu­(II) and CR by the PCA. Accordingly, pH 5.0 for CR and pH 6.0 for Cu­(II) were adopted in the following adsorption experiments.

3.3. Effects of Interfering Ions

Considering the high complexity of actual water, different interfering ions were chosen for evaluating their impact on the adsorption ability of PCA toward Cu­(II) and CR. As shown in Figure a, the presence of coexisting cations decreases the adsorption capacity of Cu­(II), and the inhibitory effect becomes more pronounced with increasing ionic concentration. Divalent ions (Ca2+ and Mg2+) exhibit stronger inhibition than monovalent ions (Na+ and K+), which is mainly attributed to their stronger interaction with O/P-containing functional groups and competition for available adsorption sites on PCA. The effects of different coexisting anions on Cu­(II) adsorption were further evaluated (Figure S2a). The addition of anions slightly enhances Cu­(II) adsorption compared with the ion-free control, while the differences among various anions are negligible, suggesting their limited contribution to Cu­(II) adsorption.

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Effect of coexisting ions and ionic strength on the adsorption of Cu­(II) (a) and CR (b) by PCA.

For CR adsorption, the presence of different coexisting anions causes a slight decrease in adsorption capacity (Figure b), which may result from competitive interactions and disturbance of the interfacial charge environment. However, coexisting cations enhance CR adsorption to different degrees (Figure S2b), with stronger effects observed for divalent ions (Ca2+ and Mg2+). This enhancement may be related to cation-induced charge screening, which weakens electrostatic repulsion among anionic CR molecules and between CR molecules and negatively charged surface domains of PCA, thereby facilitating CR accumulation at the adsorption interface.

3.4. Adsorption Kinetics

To clarify the kinetic process and possible rate-controlling steps for Cu­(II) and CR adsorption on PCA, adsorption experiments were conducted at 293.15, 303.15, and 313.15 K, and the data were analyzed with the pseudo-first-order, pseudo-second-order (PSO), and Elovich models. As illustrated in Figure a,c, the kinetic curves of adsorption for Cu­(II) and CR show the same general trend. The porous structure of PCA provides abundant adsorption sites, leading to the rapid uptake of Cu­(II) and CR within the first 10 min. As adsorption proceeds, vacant sites on PCA become progressively limited, thereby slowing the uptake of Cu­(II) and CR, with adsorption equilibrium nearly reaching within 20 min. Compared with the other models, the PSO model shows closer agreement with the experimental data, as indicated by its R 2 and χ2 values (Table S5), suggesting that it more accurately describes the uptake kinetics of both Cu­(II) and CR. This result implies that chemisorption dominates the adsorption process. During the initial stage, the active sites of the adsorbent are not yet saturated, allowing Cu­(II) and CR to be removed rapidly through surface interactions. After this initial stage, intraparticle diffusion becomes more evident as Cu­(II) and CR gradually migrate into the interior of the adsorbent. In addition, the theoretical adsorption capacities derived from the PSO model for Cu­(II) and CR are 51.10, 63.55, and 67.53 mg g–1 and 254.33, 390.15, and 504.52 mg g–1, which closely correspond to their respective experimentally measured values of 51.74, 60.44, and 64.49 mg g–1 and 239.06, 366.36, and 477.96 mg g–1, respectively, and this further demonstrates the applicability of the PSO model.

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Kinetic fitting curves for PCA adsorption of Cu­(II) (a) and CR (c) and their intraparticle diffusion model fitting curves (b, d).

To probe deeply the kinetic-controlling mechanisms and clarify the role of diffusion during adsorption, the intraparticle diffusion (IPD) model was employed for a systematic analysis of the adsorption kinetic profiles of Cu­(II) and CR. As shown in Figure b,d, the plots of qt against t (1/2) are divided into several linear regions rather than forming a single straight line, and the fitted lines fail to pass through the origin, suggesting that intraparticle diffusion contributes to Cu­(II) and CR transport within PCA, although the overall adsorption rate is also affected by other steps. The fitting curves are divided into three main phases: external surface diffusion (k p1), intraparticle diffusion (k p2), and adsorption equilibrium (k p3), where k p1 > k p2 > k p3 (Table S5), implying that external surface diffusion dominates the rate-control process. Taken together, the kinetic analysis suggests that PCA adsorbs Cu­(II) and CR through chemisorption-assisted diffusion, involving both external surface diffusion and intraparticle diffusion.

3.5. Adsorption Isotherms and Thermodynamics

Adsorption isotherms can clarify the characteristics of the adsorbed layer and the interfacial behavior between the adsorbate and adsorbent. The adsorption isotherms were determined at 293.15, 303.15, and 313.15 K and were fitted with the Langmuir and Freundlich models (Figure a,b). The Langmuir model shows higher R 2 values and lower Chi-Sqr values than the Freundlich model (Table S6), indicating that it more appropriately represents the adsorption process. Meanwhile, as the temperature increased from 293.15 to 313.15 K, the maximum adsorption capacities for both Cu­(II) and CR increase, indicating that elevated temperature favors the migration and enrichment of pollutants at the PCA surface and pore–wall interfaces. The thermodynamic parameters further reveal the effect of temperature on the adsorption process (Figure c and Table S7). The negative ΔG values signify the spontaneity of the adsorption processes for Cu­(II) and CR. The increase in adsorption capacity at higher temperatures agrees with the positive ΔH values, reflecting the endothermic nature of the adsorption process. The positive ΔS indicates that the adsorption system underwent an increase in disorder and randomness, thereby enhancing the affinity between the adsorbent and adsorbate. Taken together, the isotherm and thermodynamic analyses demonstrate that PCA possesses high adsorption capacities for Cu­(II) and CR in single-component systems, with spontaneous and endothermic adsorption behavior. Compared with reported modified carbon-based adsorbents (Table ), PCA exhibited competitive theoretical capacities, highlighting its potential for removing both heavy metal ions and dye pollutants.

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Adsorption isotherms for Cu­(II) (a) and CR (b), ln K vs 1/T plots for Cu­(II) and CR (c).

1. Comparison of the Adsorption Capacity of PCA with Various Modified Carbon-Based Materials for Cu­(II) and CR.

  q max (mg g–1)
  
adsorbent Cu(II) CR refs
AC 19.23  
MnFe2O4-PCB 32.7  
ZnFe2O4/biochar 63.29  
OPLB 60.68  
KBC   584.17
pre-H3PO4   617.28
CNF/ACF   288.13
AcBH   476.4
PCA 76.4 641.86 this work
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3.6. Application of PCA in Real Water and Its Stability

Given the strong adsorption ability of PCA toward Cu­(II) and CR, it is crucial to investigate its performance in real aqueous environments. Adsorption experiments were conducted using tap water, lake water, and river water as real water matrices. The physicochemical properties of these water samples, including pH, conductivity, total organic carbon (TOC), and major ion compositions, were analyzed and summarized in Table S8. The conductivity values of tap water, lake water, and river water are 86, 146, and 182 μS cm–1, respectively, while their TOC contents were 0.92, 2.35, and 2.86 mg L–1, indicating the presence of different levels of dissolved inorganic ions and natural organic matter in these water samples.

PCA exhibits Cu­(II) adsorption capacities of 55.30, 51.44, and 50.06 mg g–1 in tap, lake, and river water, respectively (Figure a), all slightly below the value obtained in ultrapure water; the decrease likely reflects site competition between Cu­(II) and coexisting ions in real water matrices. The reduced Cu­(II) uptake may be attributed to the competition between Cu­(II) and coexisting cations such as Na+, Ca2+, and Mg2+ for O/P-containing active sites on PCA. In contrast, PCA shows slightly higher CR adsorption capacities in real water than in ultrapure water (Figure b). This enhancement may be related to the increased ionic strength and divalent-cation-assisted charge screening, which can weaken the electrostatic repulsion between anionic CR and PCA as well as among CR molecules, thereby facilitating CR accumulation on accessible surfaces and pore walls. However, natural organic matter and competing anions may also inhibit adsorption; thus, the observed adsorption behavior should be regarded as a net result of these competing matrix effects and may vary with the specific composition of real water. ,,

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Effect of different aqueous systems on the adsorption properties of Cu­(II) (a) and CR (b); effect of adsorption–desorption cycles on the regeneration performance of PCA toward Cu­(II) (c) and CR (d) in their respective single-component systems.

Given the importance of adsorbent recovery and reuse, the regenerative capacity of PCA is regarded as an indispensable component of its economic viability and practicality. Therefore, the cycling performance of PCA was investigated separately in single-component Cu­(II) and CR systems. After five adsorption–desorption cycles, PCA retains 79.62 and 75.49% of its initial adsorption capacity for Cu­(II) and CR, respectively (Figure c,d), indicating its acceptable regenerability toward both pollutants. The gradual decrease in adsorption capacity may be attributed to slight material loss during cycling, partial occupation of active sites, and incomplete desorption of adsorbed species. Overall, PCA maintains relatively good adsorption performance after repeated use, suggesting its potential for the separate removal of heavy metal ions and dye pollutants.

3.7. Adsorption Isotherms for the Cu­(II)–CR Binary System

In order to characterize the adsorption behavior of Cu­(II) and CR in the binary system while minimizing the influence of pH variations, the adsorption isotherm experiments were conducted in a 10 mmol L–1 MES buffer at pH 6.0, and the resulting data were fitted using the Langmuir and Freundlich models. The results (Figure a,b and Table S9) showed that the adsorption behaviors of both Cu­(II) and CR on PCA in the binary system were better-described by the Langmuir model, indicating a certain saturation tendency at the accessible surface and pore–wall interfaces of PCA. As the CR concentration increased from 0 to 30 mg L–1, the Cu­(II) adsorption capacity of PCA rose from 76.40 to 87.83 mg g–1, reflecting the promoting effect of CR on Cu­(II) adsorption. Similarly, when the Cu­(II) concentration increased from 0 to 10 mg L–1, the adsorption capacity for CR significantly increased from 641.86 to 1795.32 mg g–1, representing an increase of about 3-fold, indicating that Cu­(II) had a more pronounced promoting effect on CR adsorption.

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Effect of PCA on the simultaneous adsorption of Cu­(II) (a) and CR (b) in the Cu­(II)–CR binary system and the R q values for the simultaneous removal of Cu­(II) (c) and CR (d) at different concentrations.

The effect of simultaneous adsorption was quantitatively assessed using the adsorption capacity ratio (R q). The R q of PCA for both CR and Cu­(II) (Figure c,d) are much larger than 1, indicating that the coexistence of the two pollutants promoted their adsorption on PCA. Specifically, with increasing CR concentration, the R q value of Cu­(II) increased to 1.21, whereas with increasing Cu­(II) concentration, the R q value of CR increased to 2.22. In comparison, the increase in the R q value of CR was much higher than that of Cu­(II), demonstrating that a synergistic adsorption behavior occurred in the Cu­(II)–CR binary system and that this synergy was mainly reflected in the enhancement of CR adsorption by Cu­(II), which may be attributed to the regulation of the local interfacial environment by adsorbed Cu­(II). During the binary adsorption process, Cu­(II) interacts with O/P-containing functional groups on PCA, leading to the redistribution of local surface charge and reducing the electrostatic resistance toward CR adsorption. Meanwhile, the adsorbed Cu­(II) may provide favorable interfacial regions for CR accumulation through localized Cu­(II)–CR interactions, thereby facilitating CR enrichment and immobilization on PCA. Owing to the scarcity of directly comparable studies on Cu­(II)–CR binary adsorption, representative metal cation–anionic dye systems were used as references to evaluate the synergistic performance of PCA, with emphasis on the relative enhancement of anionic pollutant adsorption under binary conditions compared with the corresponding single-component systems. The comparison indicated that PCA exhibited a pronounced synergistic enhancement in the Cu­(II)–CR system (Table ), highlighting its potential for treating wastewater containing coexisting heavy metal ions and anionic dyes.

2. Comparison of Adsorption Capacities and Enhancement Factors for Representative Metal Cation–Anionic Dye Binary Systems.

adsorbent binary system target component q single (mg g–1) q binary (mg g–1) enhancement factor references
PRAC Cu(II)–AB80 Cu(II) 26.80 45.00 1.68
LDH@GO-SH Cu(II)–MO Cu(II) 178.8 211.3 1.18
SEP/PR Pb(II)–CR Pb(II) 300.16 343.08 1.14
PCA Cu(II)–CR Cu(II) 76.40 87.83 1.15 this work
PRAC Cu(II)–AB80 AB80 173.00 294.7 1.70
LDH@GO-SH Cu(II)–MO MO 117.92 218.61 1.85
SEP/PR Pb(II)–CR CR 288.09 343.68 1.19
PCA Cu(II)–CR CR 641.86 1795.32 2.8 this work
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3.8. Mechanism Analysis

The adsorption behavior of PCA is influenced not only by its surface chemical properties but also by its porous structure and interfacial characteristics. SEM (Figure d,e) results reveal that PCA possesses a loose porous framework formed by interconnected carbon particles, providing accessible spaces for pollutant diffusion and interfacial enrichment. Meanwhile, EDS mapping (Figure S3a) shows a uniform distribution of C, O, and P elements on the PCA surface, indicating that P introduced by phytic acid is successfully incorporated into the carbon framework and provides the basis for the formation of the O/P-containing functional groups. After adsorption in the Cu­(II)–CR binary system (Figure S3b), additional S and Cu signals are observed on the PCA surface, indicating that CR and Cu­(II) are simultaneously retained at the accessible adsorption interfaces of the PCA. This finding provides elemental distribution evidence for the simultaneous adsorption of Cu­(II) and CR and supports the presence of interfacial interactions in the Cu­(II)–CR binary adsorption system.

To further investigate the adsorption mechanism of PCA toward CR and Cu­(II) in single-component and binary systems, FTIR and XPS were employed to analyze the changes in functional groups and surface chemical states before and after adsorption. In the single-component system, the FTIR results (Figure e) suggest that the O–H, C–H, PO, and P–O vibration peaks of PCA are markedly weakened after CR adsorption (PCA+CR). The weakened peak intensity can be ascribed to hydrogen bonding involving the O–H groups of CR and PCA, as well as electron donation from the N atom of CR (−NH2) to the O atom of PCA (–O−), suggesting that O–H and P-containing groups participate in CR adsorption. Through electrostatic interactions, the positively charged groups on the adsorbent surface strongly interact with the sulfonate oxygen atoms of CR molecules, leading to the attenuation of the C–H vibration peak. After Cu­(II) adsorption onto PCA (PCA+Cu­(II)), the vibration peaks of O–H, C–H, CC/CO, and PO/P–O are notably weakened. This is due to surface complexes formed between Cu­(II) and these groups. The weakening of the CC and C–H peaks may result from the formation of Cu­(II)–π interactions during Cu­(II) adsorption. In the binary system, the FTIR spectra (Figure e) show more pronounced changes in the O–H, PO, and P–O characteristic bands compared with those in the single-component systems, suggesting that the coexistence of Cu­(II) and CR enhances the interactions between pollutants and O/P-containing functional groups on PCA. Meanwhile, the preserved peak positions indicate that the original adsorption sites remain involved during the coadsorption process. These results suggest that Cu­(II) and CR are simultaneously immobilized on PCA through their interactions with surface functional groups.

XPS results (Figure f) further confirm the adsorption of Cu­(II) and CR on the PCA surface. The characteristic peaks of S 2p (167.3 eV) and N 1s (400 eV) appear after CR adsorption, whereas Cu 2p (933.8 eV) is observed after Cu­(II) adsorption. As shown in Figure g–i, the peak positions of C–OH, P–O, and PO components shift after CR and Cu­(II) adsorption, accompanied by a decrease in their relative contents, suggesting that oxygen-containing functional groups participate in hydrogen bonding or coordination interactions with CR and Cu­(II). Additionally, the appearance of a new peak at 532.1 eV, corresponding to Cu–O, further indicates that Cu­(II) can interact with oxygen-containing functional groups on the PCA surface through coordination or complexation. Based on the above single-component adsorption results, the changes in surface functional groups and interfacial charge properties of PCA under the coexistence of Cu­(II) and CR were further investigated. XPS surface elemental analysis shows that the contents of N (3.15%) and Cu (1.69%) in PCA+Cu­(II)+CR are found to be higher than those in the corresponding single-component adsorption samples (Table S10), indicating that the coexisting Cu­(II) and CR exhibited enhanced accumulation on the PCA surface, which was consistent with the increased adsorption capacities observed in the binary adsorption experiments. After CR adsorption, the S 2p spectrum splits into two main peaks at 167.6 eV (S 2p3/2) and 168.8 eV (S 2p1/2) (Figure a). However, for PCA+Cu­(II)+CR, the binding energies of S 2p3/2 and S 2p1/2 shift to 167.8 and 169.3 eV, indicating that the electronic environment of the sulfonate groups in CR is altered after coadsorption. Meanwhile, after Cu­(II) adsorption, the Cu 2p spectrum was deconvoluted into two main peaks at 935.3 eV (Cu 2p3/2) and 955.2 eV (Cu 2p1/2) (Figure b). However, for PCA+Cu­(II)+CR, the binding energies of Cu 2p3/2 and Cu 2p1/2 shifted to 936.4 and 955.8 eV, respectively, indicating that the electronic environment of the adsorbed Cu­(II) was altered after CR coadsorption. Therefore, the S 2p and Cu 2p spectra suggest that the adsorbed Cu­(II) species are not only bound to the functional groups of PCA but may also participate in interactions with CR molecules. Such interactions may involve electrostatic attraction between Cu­(II) and oxygen-containing groups in CR, especially sulfonate groups, thereby promoting the interfacial fixation of CR on PCA. Combined with the zeta-potential (Table S11) results, PCA+Cu­(II) exhibits a positive shift in surface potential compared with pristine PCA, while PCA+Cu­(II)+CR also shows a positive shift compared with PCA+CR. These results suggest that the adsorption of Cu­(II) could partially regulate the local interfacial charge environment of PCA, thereby reducing the electrostatic resistance toward CR adsorption. Therefore, the enhanced CR adsorption in the binary system can be attributed to the synergistic effects of Cu­(II) interaction with O/P-containing functional groups and Cu­(II)-mediated interfacial charge regulation, which together facilitate the enrichment and immobilization of CR on PCA.

10.

10

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S 2p XPS spectra of PCA+CR and PCA+Cu­(II)+CR (a); Cu 2p XPS spectra of PCA+Cu­(II) and PCA+Cu­(II)+CR (b); schematic diagram of the mechanism of Cu­(II) and CR removal by PCA (c).

Based on the above adsorption experiments and characterization results, the adsorption mechanisms of Cu­(II), CR, and their binary system on PCA are illustrated in Figure c. First, the porous carbon framework of PCA provides transport pathways and accessible adsorption spaces for pollutant diffusion and interfacial enrichment. Second, the O/P-containing functional groups on the PCA surface play important roles in pollutant immobilization. In the single-component systems, CR adsorption mainly involves hydrogen bonding, electrostatic interactions, and interfacial interactions associated with O/P-containing functional groups, whereas Cu­(II) adsorption is primarily governed by coordination or complexation interactions between Cu­(II) and O–H, CO, PO, and P–O functional groups. In the Cu­(II)–CR binary system, Cu­(II) interacts with O/P-containing sites on the PCA surface and regulates the local interfacial charge environment, thereby reducing the electrostatic repulsion between PCA and anionic CR and promoting CR enrichment at the adsorption interface. Meanwhile, the adsorbed Cu­(II) may interact with the sulfonate groups of CR molecules, further enhancing CR fixation. Therefore, the synergistic adsorption of Cu­(II) and CR by PCA in the binary system is mainly attributed to the combined contributions of porous structure-assisted mass transfer, O/P functional group interactions, Cu­(II)-mediated local charge regulation, and Cu­(II)–CR interfacial interactions.

4. Conclusion

In this study, CMC was used as a carbon precursor, and PA was introduced as a phosphorus source and activating agent to prepare PCA for the adsorption of Cu­(II) and CR in single and binary systems. PCA exhibited a porous carbon framework with abundant O/P-containing functional groups, facilitating pollutant diffusion and surface immobilization. In single-component systems, the adsorption processes followed the pseudo-second-order kinetic model, and the Langmuir model better described the adsorption behavior, with maximum adsorption capacities of 76.40 and 641.86 mg g–1 for Cu­(II) and CR, respectively. FTIR and XPS analyses revealed that CR adsorption involved hydrogen bonding, electrostatic interactions, and O/P functional groups, while Cu­(II) adsorption was mainly associated with coordination interactions with O–H, CO, PO, and P–O groups. In the Cu­(II)–CR binary system, the adsorption capacities increased to 87.83 and 1795.32 mg g–1 for Cu­(II) and CR, respectively, demonstrating a synergistic adsorption effect mainly reflected by Cu­(II)-promoted CR adsorption. Combined zeta-potential, FTIR, and XPS analyses suggested that this enhancement was related to Cu­(II)-mediated local charge regulation, O/P functional group interactions, and possible localized interactions between adsorbed Cu­(II) and CR sulfonate groups. After five adsorption–desorption cycles, PCA retained 79.62 and 75.49% of its initial adsorption capacities for Cu­(II) and CR, respectively, indicating good stability and reusability. This study provides insights into the development of CMC-derived phosphorus-doped carbon aerogels for the synergistic removal of heavy metal ions and anionic dyes in complex wastewater systems.

Supplementary Material

ao6c05761_si_001.pdf (338.2KB, pdf)

Acknowledgments

The authors gratefully acknowledge the support from the 2023 Central Financial Services Forestry Science and Technology Promotion Demonstration Project (2023TG28) and the Post-subsidy Program for Science and Technology Commissioners in Fujian Province (K1523014A).

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.6c05761.

  • Experimental materials, material characterization, and adsorption procedures; adsorption models and parameters; single-component adsorption kinetics, isotherms, and thermodynamics; binary Cu­(II)–CR adsorption isotherms; water-sample properties; and additional EDS, pore-structure, XPS, contact-angle, zeta-potential, coexisting-ion, and SEM–EDS mapping results (PDF)

The authors declare no competing financial interest.

References

  1. Huang Y., Zheng H., Hu X., Wu Y., Tang X., He Q., Peng S.. Enhanced selective adsorption of lead­(II) from complex wastewater by DTPA functionalized chitosan-coated magnetic silica nanoparticles based on anion-synergism. J. Hazard. Mater. 2022;422:126856. doi: 10.1016/j.jhazmat.2021.126856. [DOI] [PubMed] [Google Scholar]
  2. Liu Z., Hu Y., Zhang J., Guan Y., Zhang L., Ye P., Zhang T., Huang X., Wang M., Gao H.. Enhanced adsorption of Congo red from urea/calcium chloride co-modified biochar: Performance, mechanisms and toxicity assessment. Bioresour. Technol. 2023;388:129783. doi: 10.1016/j.biortech.2023.129783. [DOI] [PubMed] [Google Scholar]
  3. Bai Q., Huang C., Ma S., Gong B., Ou J.. Rapid adsorption and detection of copper ions in water by dual-functional ion-imprinted polymers doping with carbon dots. Sep. Purif. Technol. 2023;315:123666. doi: 10.1016/j.seppur.2023.123666. [DOI] [Google Scholar]
  4. Solayman H. M., Hossen M. A., Abd Aziz A., Yahya N. Y., Leong K. H., Sim L. C., Monir M. U., Zoh K.-D.. Performance evaluation of dye wastewater treatment technologies: A review. J. Environ. Chem. Eng. 2023;11(3):109610. doi: 10.1016/j.jece.2023.109610. [DOI] [Google Scholar]
  5. Qasem N. A. A., Mohammed R. H., Lawal D. U.. Removal of heavy metal ions from wastewater: a comprehensive and critical review. npj Clean Water. 2021;4(1):52. doi: 10.1038/s41545-021-00127-0. [DOI] [Google Scholar]
  6. Liu Y., Ke Y., Shang Q., Yang X., Wang D., Liao G.. Fabrication of multifunctional biomass-based aerogel with 3D hierarchical porous structure from waste reed for the synergetic adsorption of dyes and heavy metal ions. Chem. Eng. J. 2023;451:138934. doi: 10.1016/j.cej.2022.138934. [DOI] [Google Scholar]
  7. Sekwele K. G., Tichapondwa S. M., Mhike W.. Cellulose, graphene and graphene-cellulose composite aerogels and their application in water treatment: a review. Discover Mater. 2024;4(1):23. doi: 10.1007/s43939-024-00097-3. [DOI] [Google Scholar]
  8. Wang C., Zhu P., Huang Z., Zhang L., Xie S., Qi Z.. Carboxymethylcellulose sodium-derived carbon aerogels for solar-driven water purification. Chemosphere. 2024;358:142109. doi: 10.1016/j.chemosphere.2024.142109. [DOI] [PubMed] [Google Scholar]
  9. Jing K., Liu X., Liu T., Wang Z., Liu H.. Facile and green construction of carboxymethyl cellulose-based aerogel to efficiently and selectively adsorb cationic dyes. J. Water Process Eng. 2023;56:104386. doi: 10.1016/j.jwpe.2023.104386. [DOI] [Google Scholar]
  10. Tang Z., Lin X., Chen Y., Pan Y., Yang Y., Mondal A. K., Yu M., Wu H.. Preparation of mussel-inspired polydopamine-functionalized TEMPO-oxidized cellulose nanofiber-based composite aerogel as reusable adsorbent for water treatment. Ind. Crops Prod. 2023;206:117735. doi: 10.1016/j.indcrop.2023.117735. [DOI] [Google Scholar]
  11. Wu Z. Y., Liang H. W., Li C., Hu B. C., Xu X. X., Wang Q., Chen J. F., Yu S. H.. Dyeing bacterial cellulose pellicles for energetic heteroatom doped carbon nanofiber aerogels. Nano Res. 2014;7(12):1861–1872. doi: 10.1007/s12274-014-0546-4. [DOI] [Google Scholar]
  12. Wang W., Wang P., Wu C., Zhang L., Mao L., Zhu L., Jiang H., Zheng Y., Liu X.. Adsorption of acetochlor-contaminated water systems using novel P-doped biochar: Effects, application, and mechanism. Chemosphere. 2024;350:141027. doi: 10.1016/j.chemosphere.2023.141027. [DOI] [PubMed] [Google Scholar]
  13. Tegin İ., Öç S., Saka C., Kalderis D., Yabalak E.. Phosphorus-doped pistachio shell hydrochar for sustainable copper­(II) ion adsorption: A circular bioeconomy approach. Chem. Eng. Res. Des. 2025;223:415–424. doi: 10.1016/j.cherd.2025.10.010. [DOI] [Google Scholar]
  14. Sudarsan S., Murugesan G., Varadavenkatesan T., Vinayagam R., Selvaraj R.. Efficient adsorptive removal of Congo Red dye using activated carbon derived from Spathodea campanulata flowers. Sci. Rep. 2025;15(1):1831. doi: 10.1038/s41598-025-86032-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Zhi Y., Shao J., Wang J., Liu X., Xiao Q., Demir M., Simsek U. B., Wang L., Hu X.. Novel Synthesis of Phosphorus-Doped Porous Carbons from Lotus Petiole Using Sodium Phytate for Selective CO(2) Capture. Molecules. 2025;30(19):3990. doi: 10.3390/molecules30193990. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Duran-Uribe E. S., Villora-Picó J. J., Sepúlveda-Escribano A., Ramos-Fernandez E. V.. Surface chemistry engineering via phytic acid doping: Tailoring activated carbons for selective catalysis. Carbon. 2025;244:120701. doi: 10.1016/j.carbon.2025.120701. [DOI] [Google Scholar]
  17. Zhang H., Li R., Zhang Z.. A versatile EDTA and chitosan bi-functionalized magnetic bamboo biochar for simultaneous removal of methyl orange and heavy metals from complex wastewater. Environ. Pollut. 2022;293:118517. doi: 10.1016/j.envpol.2021.118517. [DOI] [PubMed] [Google Scholar]
  18. Ghilan A., Nita L. E., Pamfil D., Simionescu N., Tudorachi N., Rusu D., Rusu A. G., Bercea M., Rosca I., Ciolacu D. E., Chiriac A. P.. One-Step Preparation of Carboxymethyl Cellulose-Phytic Acid Hydrogels with Potential for Biomedical Applications. Gels. 2022;8(10):647. doi: 10.3390/gels8100647. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Yang X., Wan Y., Zheng Y., He F., Yu Z., Huang J., Wang H., Ok Y. S., Jiang Y., Gao B.. Surface functional groups of carbon-based adsorbents and their roles in the removal of heavy metals from aqueous solutions: A critical review. Chem. Eng. J. 2019;366:608–621. doi: 10.1016/j.cej.2019.02.119. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Guo J., Xu X., Hill J. P., Wang L., Dang J., Kang Y., Li Y., Guan W., Yamauchi Y.. Graphene-carbon 2D heterostructures with hierarchically-porous P,N-doped layered architecture for capacitive deionization. Chem. Sci. 2021;12(30):10334–10340. doi: 10.1039/D1SC00915J. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Lin G., Xiong Y., Wang G., Li S., Jiang R., Lu B., Chen Y., Huang B.. Selective and efficient removal of lanthanum ion in aqueous solution by P-doped porous carbon. J. Water Process Eng. 2023;55:104116. doi: 10.1016/j.jwpe.2023.104116. [DOI] [Google Scholar]
  22. Pimentel C. H., Díaz-Fernández L., Gómez-Díaz D., Freire M. S., González-Álvarez J.. Separation of CO2 using biochar and KOH and ZnCl2 activated carbons derived from pine sawdust. J. Environ. Chem. Eng. 2023;11(6):111378. doi: 10.1016/j.jece.2023.111378. [DOI] [Google Scholar]
  23. Chen C., Huang Y., Lu M., Zhang J., Li T.. Tuning morphology, defects and functional group types in hard carbon via phosphorus doped for rapid sodium storage. Carbon. 2021;183:415–427. doi: 10.1016/j.carbon.2021.07.040. [DOI] [Google Scholar]
  24. Wang W., Zhang H., Zhou F., Wang Y., Xiang Z., Zhu W., Wang H.. Phytic acid-assisted phase-controlled synthesis of nickel phosphides for highly selective hydrogenation of biomass-derived furfural. Appl. Catal., B. 2024;359:124413. doi: 10.1016/j.apcatb.2024.124413. [DOI] [Google Scholar]
  25. Li X., Ye L., Ye Z., Xie S., Qiu Y., Liao F., Lin C., Liu M.. N, P co-doped core/shell porous carbon as a highly efficient peroxymonosulfate activator for phenol degradation. Sep. Purif. Technol. 2021;276:119286. doi: 10.1016/j.seppur.2021.119286. [DOI] [Google Scholar]
  26. Yuan X., Xiao J., Yılmaz M., Zhang T. C., Yuan S.. N, P Co-doped porous biochar derived from cornstalk for high performance CO2 adsorption and electrochemical energy storage. Sep. Purif. Technol. 2022;299:121719. doi: 10.1016/j.seppur.2022.121719. [DOI] [Google Scholar]
  27. Zhang Z., Zhang M., Zhao X., Cao J.. High-efficient removal and adsorption mechanism of organic dyes in wastewater by KOH-activated biochar from phenol-formaldehyde resin modified wood. Sep. Purif. Technol. 2024;330:125542. doi: 10.1016/j.seppur.2023.125542. [DOI] [Google Scholar]
  28. Xu Y., Xia M., Jiang Y., Li F., Xue B.. Opal promotes hydrothermal carbonization of hydroxypropyl methyl cellulose and formation of carbon nanospheres. RSC Adv. 2018;8(36):20095–20107. doi: 10.1039/C8RA01138A. [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Dai X., Thi Hong Nhung N., Hamza M. F., Guo Y., Chen L., He C., Ning S., Wei Y., Dodbiba G., Fujita T.. Selective adsorption and recovery of scandium from red mud leachate by using phosphoric acid pre-treated pitaya peel biochar. Sep. Purif. Technol. 2022;292:121043. doi: 10.1016/j.seppur.2022.121043. [DOI] [Google Scholar]
  30. Huang K., Hu C., Tan Q., Yu M., Shabala S., Yang L., Sun X.. Highly efficient removal of cadmium from aqueous solution by ammonium polyphosphate-modified biochar. Chemosphere. 2022;305:135471. doi: 10.1016/j.chemosphere.2022.135471. [DOI] [PubMed] [Google Scholar]
  31. Qin X., Meng W., Cheng S., Xing B., Shi C., Nie Y., Wang Q., Xia H.. Efficient removal of heavy metal and antibiotics from wastewater by phosphate-modified hydrochar. Chemosphere. 2023;345:140484. doi: 10.1016/j.chemosphere.2023.140484. [DOI] [PubMed] [Google Scholar]
  32. Zhou M., Xu Y., Luo G., Zhang Q., Du L., Cui X., Li Z.. Facile synthesis of phosphorus-doped porous biochars for efficient removal of elemental mercury from coal combustion flue gas. Chem. Eng. J. 2022;432:134440. doi: 10.1016/j.cej.2021.134440. [DOI] [Google Scholar]
  33. Puziy A. M., Poddubnaya O. I., Socha R. P., Gurgul J., Wisniewski M.. XPS and NMR studies of phosphoric acid activated carbons. Carbon. 2008;46(15):2113–2123. doi: 10.1016/j.carbon.2008.09.010. [DOI] [Google Scholar]
  34. Bian P., Shao Q.. Efficient removal of copper ions, zinc ions, and tetracycline in water by functionalized Canadian horseweed hydrothermal carbon: The combination of experiment and DFT calculation. Sep. Purif. Technol. 2024;331:125557. doi: 10.1016/j.seppur.2023.125557. [DOI] [Google Scholar]
  35. Zhang Y., Zhu C., Liu F., Yuan Y., Wu H., Li A.. Effects of ionic strength on removal of toxic pollutants from aqueous media with multifarious adsorbents: A review. Sci. Total Environ. 2019;646:265–279. doi: 10.1016/j.scitotenv.2018.07.279. [DOI] [PubMed] [Google Scholar]
  36. Tang J., Zhang Y.-F., Liu Y., Li Y., Hu H.. Efficient ion-enhanced adsorption of congo red on polyacrolein from aqueous solution: Experiments, characterization and mechanism studies. Sep. Purif. Technol. 2020;252:117445. doi: 10.1016/j.seppur.2020.117445. [DOI] [Google Scholar]
  37. Nguyen T.-K.-T., Nguyen T.-B., Chen W.-H., Chen C.-W., Patel A. Kumar., Bui X.-T., Chen L., Singhania R. R., Dong C.-D.. Phosphoric acid-activated biochar derived from sunflower seed husk: Selective antibiotic adsorption behavior and mechanism. Bioresour. Technol. 2023;371:128593. doi: 10.1016/j.biortech.2023.128593. [DOI] [PubMed] [Google Scholar]
  38. Xiong Z., Zheng H., Hu Y., Hu X., Ding W., Ma J., Li Y.. Selective adsorption of Congo red and Cu­(II) from complex wastewater by core-shell structured magnetic carbon@zeolitic imidazolate frameworks-8 nanocomposites. Sep. Purif. Technol. 2021;277:119053. doi: 10.1016/j.seppur.2021.119053. [DOI] [Google Scholar]
  39. Tang J., Ma Y., Deng Z., Li P., Qi X., Zhang Z.. One-pot preparation of layered double oxides-engineered biochar for the sustained removal of tetracycline in water. Bioresour. Technol. 2023;381:129119. doi: 10.1016/j.biortech.2023.129119. [DOI] [PubMed] [Google Scholar]
  40. Zhao D., Qiu S.-k., Li M.-m., Luo Y., Zhang L.-s., Feng M.-h., Yuan M.-y., Zhang K.-q., Wang F.. Modified biochar improves the storage capacity and adsorption affinity of organic phosphorus in soil. Environ. Res. 2022;205:112455. doi: 10.1016/j.envres.2021.112455. [DOI] [PubMed] [Google Scholar]
  41. Liu B., Chen T., Wang B., Zhou S., Zhang Z., Li Y., Pan X., Wang N.. Enhanced removal of Cd2+ from water by AHP-pretreated biochar: Adsorption performance and mechanism. J. Hazard. Mater. 2022;438:129467. doi: 10.1016/j.jhazmat.2022.129467. [DOI] [PubMed] [Google Scholar]
  42. Zhao X., Liang H., Wang Z., Li D., Shen X., Xu X., Li K., Xiang Q., Wu Y., Chen Q.. Preparation of N-doped cellulose-based hydrothermal carbon using a two-step hydrothermal induction assembly method for the efficient removal of Cr­(VI) from wastewater. Environ. Res. 2023;219:115015. doi: 10.1016/j.envres.2022.115015. [DOI] [PubMed] [Google Scholar]
  43. El Kaim Billah R., Islam M. A., Nazal M. K., Bahsis L., Soufiane A., Abdellaoui Y., Achak M.. A novel glutaraldehyde cross-linked chitosan@acid-activated bentonite composite for effectivePb (II) and Cr (VI) adsorption: Experimental and theoretical studies. Sep. Purif. Technol. 2024;334:126094. doi: 10.1016/j.seppur.2023.126094. [DOI] [Google Scholar]
  44. Sveshnikova D. A., Suleimanov S. I., Rabadanova D. I., Gafurov M. M., Akhmedov I. R., Kakagasanov M. G., Rabadanov K. S., Asvarov A. S.. Adsorption of copper from aqueous solutions by activated carbon prepared from peach wood. J. Iran. Chem. Soc. 2022;19(7):3205–3214. doi: 10.1007/s13738-022-02524-9. [DOI] [Google Scholar]
  45. Huang W.-H., Wu R.-M., Chang J.-S., Juang S.-Y., Lee D.-J.. Manganese ferrite modified agricultural waste-derived biochars for copper ions adsorption. Bioresour. Technol. 2023;367:128303. doi: 10.1016/j.biortech.2022.128303. [DOI] [PubMed] [Google Scholar]
  46. Zhang X., Shu X., Zhou X., Zhou C., Yang P., Diao M., Hu H., Gan X., Zhao C., Fan C.. Magnetic reed biochar materials as adsorbents for aqueous copper and phenol removal. Environ. Sci. Pollut. Res. 2023;30(2):3659–3667. doi: 10.1007/s11356-022-22474-2. [DOI] [PubMed] [Google Scholar]
  47. Iamsaard K., Weng C.-H., Tzeng J.-H., Anotai J., Jacobson A. R., Lin Y.-T.. Systematic optimization of biochars derived from corn wastes, pineapple leaf, and sugarcane bagasse for Cu­(II) adsorption through response surface methodology. Bioresour. Technol. 2023;382:129131. doi: 10.1016/j.biortech.2023.129131. [DOI] [PubMed] [Google Scholar]
  48. Liu Z., Zhang J., Zhang L., Guan Y., Ji H., Zhang Y., Gao H.. Efficient removal of Congo red and methylene blue using biochar from Medulla Tetrapanacis modified by potassium carbonate. Bioresour. Technol. 2023;376:128912. doi: 10.1016/j.biortech.2023.128912. [DOI] [PubMed] [Google Scholar]
  49. Sangon S., Hunt A. J., Attard T. M., Mengchang P., Ngernyen Y., Supanchaiyamat N.. Valorisation of waste rice straw for the production of highly effective carbon based adsorbents for dyes removal. J. Cleaner Prod. 2018;172:1128–1139. doi: 10.1016/j.jclepro.2017.10.210. [DOI] [Google Scholar]
  50. Tu W., Liu Y., Xie Z., Chen M., Ma L., Du G., Zhu M.. A novel activation-hydrochar via hydrothermal carbonization and KOH activation of sewage sludge and coconut shell for biomass wastes: Preparation, characterization and adsorption properties. J. Colloid Interface Sci. 2021;593:390–407. doi: 10.1016/j.jcis.2021.02.133. [DOI] [PubMed] [Google Scholar]
  51. Yang X., Wang L., Shao X., Tong J., Zhou J., Feng Y., Chen R., Yang Q., Han Y., Yang X., Ding F., Meng Q., Yu J., Zimmerman A. R., Gao B.. Characteristics and aqueous dye removal ability of novel biosorbents derived from acidic and alkaline one-step ball milling of hickory wood. Chemosphere. 2022;309:136610. doi: 10.1016/j.chemosphere.2022.136610. [DOI] [PubMed] [Google Scholar]
  52. Wang X., Wang J., Jiang L., Jiang Y.. Adsorption of Pb2+ and Cu2+ in wastewater by lignosulfonate adsorbent prepared from corn straw. Int. J. Biol. Macromol. 2023;247:125820. doi: 10.1016/j.ijbiomac.2023.125820. [DOI] [PubMed] [Google Scholar]
  53. Wang Q., Tian Y., Kong L., Zhang J., Zuo W., Li Y., Cai G.. A novel 3D superelastic polyethyleneimine functionalized chitosan aerogels for selective removal of Cr­(VI) from aqueous solution: performance and mechanisms. Chem. Eng. J. 2021;425:131722. doi: 10.1016/j.cej.2021.131722. [DOI] [Google Scholar]
  54. Yu Z., Wu Z., Sheng R., Liu C., Chen H., Zhang J., Qiu Z.. Ultra-high adsorption of CR from aqueous solution using LDHs decorated magnetic hydrochar: Selectivity and anti-interference exploration. Sep. Purif. Technol. 2023;313:123438. doi: 10.1016/j.seppur.2023.123438. [DOI] [Google Scholar]
  55. Gkika D. A., Tolkou A. K., Katsoyiannis I. A., Kyzas G. Z.. The adsorption-desorption-regeneration pathway to a circular economy: The role of waste-derived adsorbents on chromium removal. Sep. Purif. Technol. 2025;368:132996. doi: 10.1016/j.seppur.2025.132996. [DOI] [Google Scholar]
  56. Peng H., Gao P., Chu G., Pan B., Peng J., Xing B.. Enhanced adsorption of Cu­(II) and Cd­(II) by phosphoric acid-modified biochars. Environ. Pollut. 2017;229:846–853. doi: 10.1016/j.envpol.2017.07.004. [DOI] [PubMed] [Google Scholar]
  57. Luo X., Zhang Z., Zhou P., Liu Y., Ma G., Lei Z.. Synergic adsorption of acid blue 80 and heavy metal ions (Cu2+/Ni2+) onto activated carbon and its mechanisms. J. Ind. Eng. Chem. 2015;27:164–174. doi: 10.1016/j.jiec.2014.12.031. [DOI] [Google Scholar]
  58. Liao W., Li H., Yu X., Li Y.. Simultaneous Removal of Cu­(II) and Dyes from Aqueous Solution Using LDH@GO-SH as an Adsorbent. Water. 2024;16(14):1968. doi: 10.3390/w16141968. [DOI] [Google Scholar]
  59. Wang Z., Huang P., Yan Y., Tao Y., Lei W., Xia M., Wang F.. Effective removal of Pb­(II) and Congo red by polyrhodanine-modified sepiolite. J. Water Process Eng. 2023;54:104008. doi: 10.1016/j.jwpe.2023.104008. [DOI] [Google Scholar]
  60. Zhang D., Zhou D. L., Lu L., Zhang M., Lü T., Huang J. G., Zhao H. T., Zhou J., Rinklebe J.. Preferential, synergistic sorption and reduction of Cr­(VI) from chromium-rhodamine B mixed wastewater by magnetic porous biochar derived from wasted Myriophyllum aquaticum biomass. Environ. Pollut. 2023;327:121593. doi: 10.1016/j.envpol.2023.121593. [DOI] [PubMed] [Google Scholar]
  61. Zhou Y., Xiao J., Hu R., Wang T., Shao X., Chen G., Chen L., Tian X.. Engineered phosphorous-functionalized biochar with enhanced porosity using phytic acid-assisted ball milling for efficient and selective uptake of aquatic uranium. J. Mol. Liq. 2020;303:112659. doi: 10.1016/j.molliq.2020.112659. [DOI] [Google Scholar]
  62. Samal A., Das D. P., Madras G.. Repercussion of Solid state vs. Liquid state synthesized p-n heterojunction RGO-copper phosphate on proton reduction potential in water. Sci. Rep. 2018;8(1):2881. doi: 10.1038/s41598-018-21239-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  63. Liu B., Lv P., Wu R., Bai Y., Wang J., Su W., Song X., Yu G.. Coal gasification fine slag based multifunctional nanoporous silica microspheres for synergistic adsorption of Pb­(II) and Congo red. Sep. Purif. Technol. 2023;323:124478. doi: 10.1016/j.seppur.2023.124478. [DOI] [Google Scholar]
  64. Zhang X., Qin C., Gong Y., Song Y., Zhang G., Chen R., Gao Y., Xiao L., Jia S.. Co-adsorption of an anionic dye in the presence of a cationic dye and a heavy metal ion by graphene oxide and photoreduced graphene oxide. RSC Adv. 2019;9(10):5313–5324. doi: 10.1039/C8RA09438A. [DOI] [PMC free article] [PubMed] [Google Scholar]
  65. Lim S., Kim J. H., Park H., Kwak C., Yang J., Kim J., Ryu S. Y., Lee J.. Role of electrostatic interactions in the adsorption of dye molecules by Ti(3)­C(2)-MXenes. RSC Adv. 2021;11(11):6201–6211. doi: 10.1039/D0RA10876F. [DOI] [PMC free article] [PubMed] [Google Scholar]

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