Green Preparation of Waste-Derived Nanocellulose/Chitosan/Ag Aerogels for Multifunctional Water Treatment

Summary

This study presents recoverable nanocellulose/chitosan aerogels embedded with green-synthesized silver nanoparticles derived from sugarcane bagasse. The optimized composite exhibits balanced multifunctionality, delivering robust antibacterial activity, efficient catalytic 4-nitrophenol reduction, and enhanced dye and heavy metal adsorption with highly controlled silver release.

Abstract

​Waste-derived nanocellulose aerogels offer a sustainable route for converting lignocellulosic residues into functional porous materials, but balancing antibacterial activity, catalytic performance, adsorption capacity, and Ag-release control remains challenging. In this study, sugarcane bagasse was used as a biomass source to prepare waste-derived nanocellulose through alkaline treatment, hydrogen peroxide bleaching, high-pressure homogenization, and sonication. The nanocellulose was combined with chitosan to form porous aerogels by freezing and freeze-drying, followed by in situ green loading of Ag nanoparticles using standardized green tea extract as the reducing medium. The optimized Ag-WNC/CS-A-3 aerogel retained high porosity, improved mechanical stability, and a BET surface area of 66.4 ± 5.2 m²/g. It showed strong antibacterial activity against Escherichia coli and Staphylococcus aureus, efficient 4-nitrophenol reduction with an apparent rate constant of 0.184 ± 0.017 min⁻¹, and enhanced adsorption toward methylene blue and Pb(II), with equilibrium capacities of 118.7 ± 7.1 mg/g and 72.4 ± 6.3 mg/g, respectively. Although higher Ag loading slightly improved antibacterial and catalytic performance, it reduced adsorption balance and increased Ag release. Overall, Ag-WNC/CS-A-3 provided the most balanced combination of structural integrity, multifunctional activity, reuse stability, and Ag-release control. This work supports a sustainable design strategy for recoverable bio-based aerogels in antibacterial, catalytic, and water-treatment applications.

Introduction

The conversion of agricultural waste into functional materials has become an important direction in sustainable materials science. Sugarcane bagasse is particularly attractive because it is generated in large quantities during sugar and juice processing and contains a high proportion of cellulose that can be recovered for value-added applications. Recent work has emphasized that sugarcane bagasse is a low-cost and environmentally relevant biomass source, although efficient cellulose extraction, functionalization, and scalable nanostructure production remain key technical challenges¹. This makes bagasse-derived nanocellulose a suitable platform for developing porous materials that combine waste valorization with environmental functionality.

Nanocellulose has received increasing attention in water treatment and environmental applications due to its renewable origin, nanoscale fibrillar structure, abundant hydroxyl groups, and high surface modifiability. A recent review summarized that nanocellulose-based materials can be processed into powders, films, membranes, hydrogels, aerogels, and three-dimensional objects for removing dyes, heavy metals, drugs, pesticides, microbial cells, and other pollutants from water². Among these formats, aerogels are especially promising because they combine low density, high porosity, large accessible surface area, and easy recovery after use.

Nanocellulose aerogel fabrication generally involves nanocellulose preparation, gel formation, solvent exchange or direct freezing, and drying. These steps allow nanocellulose fibrils to assemble into a three-dimensional porous network³. Such aerogels have been widely explored for the adsorption of dyes, heavy-metal ions, antibiotics, organic solvents, and oil-water mixtures because their open pore structures facilitate mass transfer while their surface functional groups provide interaction sites for pollutants. However, nanocellulose-only aerogels often suffer from weak wet stability, limited mechanical strength, and insufficient multifunctionality, which restrict their practical use.

To overcome these limitations, composite aerogels based on cellulose and chitosan have attracted attention. Chitosan contains amino and hydroxyl groups that can interact with cellulose through hydrogen bonding and may also provide additional binding sites for metal ions and organic pollutants. Bio-based aerogels derived from cellulose and chitosan have been described as emerging materials for water treatment because their low density, high surface area, porous structure, and tunable surface chemistry can support adsorption and reuse⁴. In nanocellulose aerogels, chitosan can therefore act not only as a structural reinforcing component but also as a functional polymer that improves pollutant binding and antibacterial potential.

In addition to adsorption, multifunctional aerogels are increasingly expected to provide catalytic and antimicrobial functions. This is particularly relevant for water-treatment materials that may encounter both chemical pollutants and microbial contamination. Silver nanoparticles are widely used in functional materials because of their antimicrobial and catalytic properties. When immobilized on cellulose-based supports, Ag nanoparticles can be recovered more easily and may show improved dispersion compared with unsupported nanoparticles⁵. Green-synthesized nano-silver/cellulose aerogels have been reported as recyclable catalysts for nitrophenol hydrogenation, indicating that cellulose aerogels can serve as robust carriers for Ag-based catalytic systems⁶.

Green synthesis strategies are also important because conventional nanoparticle synthesis may involve strong reducing agents or stabilizers that reduce the environmental advantage of biomass-based materials. Plant extracts rich in polyphenols can reduce Ag⁺ to Ag nanoparticles while also contributing to stabilization during particle formation. Green tea extract has been used for AgNP synthesis because its phenolic compounds can serve as reducing and capping agents⁷. However, extract-based synthesis also introduces batch variability, making extract standardization necessary when the method is intended to be reproducible.

Despite these advances, several gaps remain. First, many studies focus on a single function, such as dye adsorption, heavy-metal removal, antibacterial activity, or 4-nitrophenol reduction, rather than evaluating how these functions can be balanced in one recoverable aerogel system. Second, higher Ag loading is often associated with stronger antibacterial or catalytic activity, but excessive Ag may block pores, reduce adsorption capacity, increase release, and weaken the sustainability profile of the material. Third, adsorption performance is frequently evaluated in single-pollutant solutions, while coexisting ions and more complex water matrices can substantially affect practical performance⁸. These issues suggest that multifunctional aerogel design should move beyond maximum activity and consider structure–function balance.

Compared with previously reported cellulose/chitosan/Ag aerogels, the present system is distinguished by four linked design features: the cellulose scaffold is prepared from sugarcane bagasse waste; the AgNP formation step uses standardized green tea extract rather than an uncharacterized plant extract batch; three Ag precursor levels are compared to identify a performance balance instead of a maximum-loading formulation; and antibacterial activity, 4-nitrophenol catalysis, dye/heavy-metal adsorption, regeneration, matrix tolerance, and Ag release are evaluated together. This comparison-based design clarifies that the novelty lies in the integrated structure-property-performance balance rather than in the mere combination of cellulose, chitosan, and Ag.

Accordingly, this study developed a waste-derived nanocellulose (WNC)/chitosan (CS)/silver nanoparticle (AgNP) aerogel using sugarcane bagasse as the cellulose source and standardized green tea extract for in situ AgNP loading. The aerogels were evaluated through multimodal characterization, including transmission electron microscopy (TEM), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) surface-area analysis, thermogravimetric analysis (TGA), and mechanical testing. Functional performance was assessed through CFU-based antibacterial assays against Escherichia coli and Staphylococcus aureus, catalytic reduction of 4-nitrophenol, adsorption of methylene blue and Pb(II), regeneration testing, coexisting-ion interference, simulated wastewater evaluation, and Ag-release analysis. This design builds on recent work showing the potential of cellulose-based and nanocellulose-based aerogels for pollutant removal, while addressing the need for multifunctional performance assessment and Ag-release control⁹.

The central hypothesis was that an intermediate Ag loading level would provide a more balanced formulation than either low or excessive Ag loading. In this design, nanocellulose provides the porous scaffold, chitosan reinforces the structure and contributes adsorption sites, and AgNPs introduce antibacterial and catalytic activity. Recent studies on cellulose-based Ag composite aerogels have shown that Ag incorporation can improve antimicrobial and catalytic functions, but the supporting matrix and release behavior remain crucial for practical performance¹⁰. Therefore, the present study compares three Ag loading levels to identify the formulation that best balances porosity, mechanical stability, antibacterial activity, catalytic efficiency, adsorption capacity, reusability, and Ag-release control.

The broader significance of this work lies in the integration of waste valorization and multifunctional water-treatment material design. Recent reviews on cellulose-based aerogels and biomass-based aerogels have highlighted their potential in adsorption, catalysis, oil-water separation, insulation, and biomedical applications, while also emphasizing the need for greener preparation, better scalability, regeneration stability, and environmental safety^11,12. By linking waste-derived nanocellulose preparation with chitosan reinforcement, green AgNP loading, and multimodal performance evaluation, this study provides a practical framework for developing recoverable bio-based aerogels for antibacterial, catalytic, and adsorption applications.

Protocol

Materials and experimental design

Sugarcane bagasse was used as the lignocellulosic waste source for nanocellulose preparation. Fresh bagasse was washed with tap water and deionized water, dried at 60 °C for 24 h, cut into 1–2 cm fragments, milled, and passed through a 40-mesh sieve. The dried powder was stored in sealed polyethylene bags with silica gel at room temperature and used within 1 month. All the reagents, materials, and equipment used in this study are listed in the Table of Materials file.

Unless otherwise specified, all chemicals were analytical grade and used as received. Sodium hydroxide, hydrogen peroxide, acetic acid, silver nitrate, sodium borohydride, 4-nitrophenol, methylene blue, lead nitrate, hydrochloric acid, nitric acid, sodium chloride, calcium chloride, magnesium chloride, ethanol, Folin-Ciocalteu reagent, sodium carbonate, and gallic acid were used for pretreatment, Ag loading, catalytic testing, adsorption, regeneration, and analytical calibration. Silver nitrate (ACS reagent, ≥99.0%), sodium borohydride (≥98.0%), Folin-Ciocalteu reagent (1.9–2.1 N), and gallic acid standard specifications are listed in the Table of Materials. Chitosan with a deacetylation degree of 85%–90% was used as the secondary biopolymer. Green tea leaves were used to prepare the aqueous reducing extract for Ag nanoparticle formation, as tea polyphenols can act as reducing and stabilizing agents during AgNP synthesis¹³. The overall workflow included cellulose extraction, nanocellulose preparation, aerogel fabrication, AgNP loading, structural characterization, and functional testing, as shown in Figure 1. The sample compositions and preparation parameters are listed in Table 1.

Sugarcane bagasse was pretreated by washing, drying, milling, alkaline treatment, and hydrogen peroxide bleaching to obtain cellulose-rich pulp. The pulp was converted into waste-derived nanocellulose through high-pressure homogenization and sonication, then combined with chitosan to fabricate nanocellulose/chitosan aerogels by freezing and freeze-drying. Ag nanoparticles were loaded in situ using AgNO₃ and standardized green tea extract as the reducing medium. The resulting aerogels were evaluated by multimodal structural, chemical, thermal, and mechanical characterization, followed by antibacterial, catalytic, adsorption, regeneration, and Ag-release assessments. Ag-WNC/CS-A-3 was selected as the optimized multifunctional aerogel formulation.

Preparation of cellulose-rich pulp

Dried bagasse powder was treated with 4 wt% NaOH at a solid-to-liquid ratio of 1:20 g/mL. The mixture was heated at 80 °C for 3 h under stirring at 500 rpm. The treated fibers were filtered and washed with deionized water until the filtrate reached pH 7.0 ± 0.2, then dried at 60 °C for 12 h.

The alkali-treated fibers were bleached with 3 wt% H₂O₂ at pH 11.0 ± 0.2 and 80 °C for 2 h. The bleaching process was repeated twice. The obtained cellulose-rich pulp was washed to neutral pH and stored in deionized water at 4 °C for no longer than 7 days. Cellulose, hemicellulose, lignin, and ash contents were determined by gravimetric compositional analysis to confirm the removal of non-cellulosic components¹⁴.

Pulp yield was calculated as:

   (1)

Preparation of waste-derived nanocellulose

Wet cellulose pulp equivalent to 5.0 g dry mass was dispersed in 500 mL of deionized water and pre-homogenized at 10,000 rpm for 10 min. The suspension was then processed by high-pressure homogenization: two passes at 300 bar, three passes at 600 bar, and five passes at 900 bar. The outlet temperature was maintained below 35 °C using an ice-water circulation system.

The homogenized suspension was sonicated at 400 W for 10 min under pulse mode, with 3 s on and 3 s off. The vessel was kept in an ice bath during sonication. The final suspension was diluted to 1.0 wt% and stored at 4 °C. Suspensions showing visible sedimentation or phase separation after 24 h were discarded. Nanocellulose preparation was accepted only when the average TEM fiber diameter was below 50 nm, and the absolute zeta potential exceeded 25 mV.

Nanocellulose yield was calculated as:

    (2)

Preparation and standardization of green tea extract

Green tea powder, 5.0 g, was added to 100 mL of deionized water and heated at 80 °C for 30 min. The extract was cooled, filtered through Whatman No. 1 filter paper, centrifuged at approximately 7,500 × g for 10 min (equivalent to about 8,000 rpm for a 10.5 cm rotor radius), filtered through a 0.45 µm membrane, and stored at 4 °C for no longer than 48 h.

The total phenolic content was measured using the Folin-Ciocalteu method. Briefly, 0.5 mL of diluted extract was mixed with 2.5 mL of diluted Folin-Ciocalteu reagent and 2.0 mL of 7.5 wt% sodium carbonate. After incubation in the dark for 30 min, absorbance was measured at 765 nm. Gallic acid was used as the standard. Only extract batches with total phenolic content within ±10% of the batch mean were used for AgNP reduction.

Fabrication of nanocellulose/chitosan aerogels

Chitosan was dissolved in 1.0 vol% acetic acid to prepare a 1.0 wt% solution and stirred overnight. The solution was filtered through a 100 µm nylon mesh before use.

For WNC/CS-A preparation, 80 mL of 1.0 wt% nanocellulose suspension was mixed with 20 mL of 1.0 wt% chitosan solution at 600 rpm. The pH was adjusted dropwise to 5.5 ± 0.2 using 0.1 M NaOH at a rate below 0.5 mL/min. The mixture was discarded if visible flocculation or phase separation appeared within 30 min.

A fixed volume of 5.0 mL dispersion was poured into cylindrical polypropylene molds with an inner diameter of 20 mm and a height of 20 mm. The samples were frozen at -80 °C for 12 h and freeze-dried at -55 °C for 48 h under a chamber pressure below 20 Pa. Freeze-drying was used to preserve the porous nanocellulose network during aerogel formation¹⁵. WNC-A was prepared using the same procedure without chitosan. The dry aerogel was accepted only when it retained a monolithic shape and showed height shrinkage below 20%.

In situ green loading of Ag nanoparticles

Dried WNC/CS-A monoliths were immersed in 30 mL of AgNO₃ solution at 1, 3, or 5 mM for 6 h in the dark. The aerogels were then transferred into 30 mL of standardized green tea extract and reacted at 50 °C for 4 h in the dark. After reduction, the samples were washed five times with deionized water, frozen at -80 °C for 6 h, and freeze-dried at -55 °C for 36 h. The final samples were coded as Ag-WNC/CS-A-1, Ag-WNC/CS-A-3, and Ag-WNC/CS-A-5. Ag immobilization in cellulose aerogels improves catalyst recovery and reduces nanoparticle loss compared with unsupported AgNP systems¹⁶.

Ag loading was quantified by Inductively coupled plasma-optical emission spectroscopy (ICP-OES). Approximately 20 mg of Ag-loaded aerogel was digested in diluted nitric acid at 80 °C, diluted to 50 mL, and analyzed using an Ag calibration curve of 0.01–5.0 mg/L. Ag loading efficiency was calculated as:

    (3)

The green-process indicators used for yield, reagent use, Ag loading, Ag release, and reuse evaluation are summarized in Table 2.

Density, porosity, water uptake, and dimensional stability

Aerogel density was calculated from dry mass and geometric volume. Samples were dried at 60 °C for 6 h, cooled in a desiccator, and measured with a digital caliper at three positions.

    (4)

Porosity was estimated as:

    (5)

where ρ_s was taken as 1.50 g/cm³ for cellulose-based solids.

Water uptake was measured by immersing dry aerogels in deionized water for 24 h. Samples were blotted for 10 s and weighed immediately.

     (6)

where W_s and W_d are the weights of wet and dry aerosols. Dimensional stability was assessed by comparing height and diameter before and after immersion. At least five monoliths were tested per group.

Morphological and porous-structure characterization

Nanocellulose morphology was observed by TEM. A 0.005 wt% suspension was dropped onto a carbon-coated copper grid, stained with 1 wt% phosphotungstic acid for 60 s, dried, and imaged at 80–120 kV. At least 100 fibers from three independent suspensions were measured using ImageJ version 1.54.

Aerogel morphology was observed by SEM. Samples were fractured in liquid nitrogen, mounted on aluminum stubs, sputter-coated with gold for 60 s, and imaged at 5–10 kV. At least five fields were recorded per sample. EDS mapping was performed to determine the distribution of Ag, C, O, and N.

Nitrogen adsorption-desorption analysis was performed at 77 K. Samples were degassed at 60 °C for 12 h before analysis. BET surface area and Barrett-Joyner-Halenda (BJH) pore size distribution were calculated because pore accessibility directly affects adsorption and catalytic performance in cellulose aerogels¹⁷.

FTIR, XRD, XPS, and TGA analysis

FTIR spectra were collected in ATR mode from 4000 cm^-1 to 500 cm^-1 at 4 cm^-1 resolution with 32 scans per sample. Spectra were baseline-corrected and normalized to the cellulose C-O-C band near 1050 cm^-1. FTIR was used to evaluate cellulose- and chitosan-related functional groups; Ag formation was confirmed by XRD, XPS, EDS, and ICP-OES.

XRD was performed using Cu K-alpha radiation at 40 kV and 40 mA. Samples were scanned from 5° to 80° at 5°/min. The cellulose crystallinity index was calculated by the Segal method. Crystalline metallic Ag was assigned only when diffraction peaks near 38.1°, 44.3°, and 64.4° were detectable, and Ag formation was interpreted together with XPS, EDS mapping, and ICP-OES rather than from XRD alone.

XPS was used to determine surface elemental composition. Survey spectra were recorded from 0 eV to 1200 eV, and high-resolution spectra were collected for C 1s, O 1s, N 1s, and Ag 3d. Binding energies were calibrated to C 1s at 284.8 eV. Peak fitting was performed using CasaXPS version 2.3.25. Ag 3d fitting was used as supporting evidence for surface Ag species; because Auger parameter analysis was not included, the relative contributions of metallic Ag0 and oxidized Ag species were interpreted cautiously.

TGA was performed under nitrogen from 30 °C to 700 °C at 10 °C/min. Approximately 5–8 mg of dried sample was used for each run. The onset degradation temperature, maximum degradation temperature, and residual mass at 700 °C were recorded.

Mechanical testing

Compression tests were performed using a universal testing machine equipped with a 100 N load cell. Cylindrical samples of 20 mm diameter and 20 mm height were compressed to 50% strain at 2 mm/min. Compressive stress at 50% strain and Young's modulus below 10% strain were calculated.

Cyclic compression was performed for five loading-unloading cycles at 50% strain. Shape recovery was calculated from the recovered height after each cycle. At least five specimens were tested per group. Samples with slipping, edge tearing before 20% strain, or visible defects were excluded. Mechanical testing was used to evaluate handling stability during immersion, recovery, and reuse¹⁸.

Antibacterial assay

Antibacterial activity was evaluated against Escherichia coli and Staphylococcus aureus. Bacteria were cultured in Luria-Bertani (LB) broth at 37 °C overnight and diluted to approximately 1 × 10⁶ CFU/mL. The concentration was verified by plate counting.

Aerogel discs of 10 mm diameter and 3 mm thickness were sterilized by UV irradiation for 30 min on each side. Sterility was confirmed by incubating treated aerogels in LB broth at 37 °C for 24 h.

For contact-killing assays, sterile aerogel discs were incubated in 2 mL of bacterial suspension at 37 °C for 4 h with shaking at 120 rpm. The suspension was serially diluted, plated on LB agar, and incubated at 37 °C for 24 h. Bacterial reduction was calculated as:

    (7)

Controls included PBS only, sterile filter-paper disc, WNC-A, WNC/CS-A, AgNO₃ solution with Ag concentration equivalent to the measured release from Ag-WNC/CS-A-3, and a commercial antibiotic disc.

For inhibition-zone assays, aerogel discs were placed on agar plates spread with 100 µL of bacterial suspension. Plates were incubated at 37 °C for 24 h, and inhibition-zone diameters were measured. Each assay used three independent aerogel batches with technical triplicates. Both contact-killing and inhibition-zone assays were used because surface contact and released Ag species may contribute differently to antibacterial activity¹⁹.

Catalytic reduction of 4-nitrophenol

Catalytic activity was evaluated using the reduction of 4-nitrophenol to 4-aminophenol. A 0.10 mM 4-nitrophenol solution was mixed with freshly prepared NaBH₄ to obtain a final NaBH₄ concentration of 10 mM. NaBH₄ was used within 30 min after preparation. The reaction was protected from direct light.

A 10.0 mg ± 0.5 mg aerogel sample was added to 10 mL of reaction solution at room temperature. At 1 min intervals, 1 mL aliquots were measured by UV-Vis spectroscopy from 250 nm to 500 nm and returned to the reaction vessel. The absorbance at 400 nm was used to monitor conversion.

Controls included a reaction without aerogel, WNC-A, WNC/CS-A, and a parallel adsorption control without NaBH4 to distinguish catalytic reduction from 4-nitrophenol adsorption. The no-NaBH4 adsorption control was treated as a physical-removal blank; only the additional decrease in the NaBH4-containing system was interpreted as catalytic conversion. The pseudo-first-order rate constant was calculated as:

Conversion was calculated as:

    (8)

The 4-nitrophenol reduction assay was selected because it is a standard UV-Vis-traceable reaction for evaluating supported Ag catalysts²⁰.

Catalytic reusability

Ag-WNC/CS-A-3 was reused for five catalytic cycles. After each cycle, the aerogel was removed, washed three times with deionized water, immersed in deionized water for 10 min, and freeze-dried at −55 °C for 12 h. Conversion at 15 min and k_app were recorded for each cycle.

    (9)

After five cycles, the used aerogel was analyzed by SEM and ICP-OES to evaluate structural retention and Ag loss.

Methylene blue adsorption

Methylene blue was used as the model cationic dye. Dried aerogel, 20.0 mg ± 0.5 mg, was added to 50 mL of 50 mg/L MB solution at pH 7.0 ± 0.2. The mixture was shaken at 150 rpm and 25 ± 1 °C.

At 5, 10, 20, 30, 60, 90, 120, and 180 min, 1 mL aliquots were collected, filtered through a 0.22 µm membrane, and measured at 664 nm. MB concentration was calculated using a calibration curve from 1 to 50 mg/L with R² ≥ 0.995.

    (10)

Kinetic data were fitted using pseudo-first-order and pseudo-second-order models. Model selection considered R², agreement between calculated and experimental q_e, and residual distribution. MB was selected because nanocellulose aerogels are commonly evaluated for dye removal through electrostatic interaction, hydrogen bonding, and porous-network diffusion²¹.

Pb(II) adsorption

Pb(II) adsorption was tested using lead nitrate solution. A 1000 mg/L stock solution was diluted before use. Dried aerogel, 20.0 mg ± 0.5 mg, was added to 50 mL of 50 mg/L Pb(II) solution at pH 5.5 ± 0.2. The mixture was shaken at 150 rpm and 25 °C ± 1 °C for 180 min.

Aliquots were filtered through a 0.22 µm membrane, acidified with 1 vol% nitric acid, and analyzed by ICP-OES. Blank controls without aerogel were run at the same initial pH as the adsorption samples, and controls without Pb(II) were included to check background signals.

For isotherm analysis, Pb(II) concentrations of 10, 25, 50, 75, 100, and 150 mg/L were tested for 24 h. Langmuir and the Freundlich models were used for equilibrium fitting. Pb(II) was used to assess binding by oxygen- and nitrogen-containing groups within the aerogel network²². Because Pb(II) speciation and precipitation risk are sensitive to pH and contact time, Pb(II) was interpreted primarily through pH-controlled endpoint and equilibrium/isotherm data; kinetic model parameters are therefore reported for MB only.

pH, coexisting ions, and water-matrix effects

The effect of pH was tested at pH 3.0, 5.0, 7.0, and 9.0 for MB, and at pH 3.0, 4.5, 5.5, and 6.5 for Pb(II). Pb(II) adsorption was not tested under alkaline conditions to avoid precipitation. Initial and final pH were recorded, and adsorption runs were repeated when pH drift exceeded 0.5 units. Same-pH blank controls without aerogel were used to distinguish aerogel adsorption from pH-dependent Pb(II) loss or precipitation.

The effect of coexisting ions was evaluated by adding 10 mM NaCl, 5 mM CaCl₂, or 5 mM MgCl₂. A mixed-ion condition containing all three salts was also tested. Simulated wastewater contained 10 mM NaCl, 2 mM CaCl₂, 2 mM MgCl₂, and 5 mg/L humic acid. The pH was adjusted to 7.0 ± 0.2 for MB and 5.5 ± 0.2 for Pb(II). These tests were included to evaluate adsorption performance under more complex water matrices²³.

Adsorption regeneration

Ag-WNC/CS-A-3 was regenerated for five adsorption cycles. For MB, loaded aerogels were immersed in a 30 mL ethanol/water solution at 50:50 v/v for 2 h. For Pb(II), loaded aerogels were immersed in 30 mL of 0.05 M HCl for 1 h and washed to pH 6.5–7.0. After each regeneration step, samples were freeze-dried at -55 °C for 12 h.

    (11)

Aerogel dry mass was recorded before and after each cycle. Samples with visible collapse, fragmentation, or dry mass loss greater than 15% were classified as structurally failed.

Ag release

Ag release was tested by immersing 20.0 ± 0.5 mg of Ag-loaded aerogel in 50 mL of deionized water, 0.9 wt% NaCl solution, or pH 5.5 acetate buffer at 25 ± 1 °C. At 24 h and 72 h, 2 mL aliquots were collected, acidified with 1 vol% nitric acid, and analyzed by ICP-OES. The sampled volume was replaced with fresh medium.

Ag release was reported as µg/L and as a percentage of total loaded Ag:

    (12)

This assay was used to evaluate whether increased Ag loading caused unnecessary Ag leaching while maintaining antibacterial and catalytic performance²⁴.

Software and data processing

SEM and TEM images were analyzed using ImageJ version 1.54. FTIR spectra, XRD patterns, UV–Vis kinetic curves, adsorption kinetics, and isotherm plots were processed using OriginPro 2024. XPS spectra were fitted using CasaXPS version 2.3.25. Statistical analysis and graph preparation were performed using GraphPad Prism 10.

For adsorption fitting, models were not selected by R² alone. Agreement between experimental and calculated adsorption capacity, residual distribution, and physical plausibility of parameters was also considered²⁵.

Quality control and statistical analysis

All experiments were performed using aerogels from at least three independent fabrication batches. Physical and mechanical tests used five specimens per group. Antibacterial, catalytic, adsorption, regeneration, and Ag-release assays used three independent batches with technical triplicates when applicable.

Aerogel batches were accepted only when the dry density variation within the same group was below 15%. Antibacterial plates were accepted when colony numbers were within 30–300 CFU. Catalytic tests were repeated when the initial absorbance at 400 nm varied by more than 10% from the batch mean. Adsorption tests were repeated when pH drift exceeded 0.5 units. ICP-OES and UV–Vis calibration curves required R² ≥ 0.995.

Data are presented as mean ± standard deviation. Normality was assessed using the Shapiro–Wilk test. Normally distributed data were analyzed by one-way ANOVA followed by Tukey's post hoc test. Non-normal data were analyzed by the Kruskal-Wallis test followed by Dunn's multiple-comparison test. A p-value below 0.05 was considered statistically significant. No outlier was removed unless a documented technical reason was present.

Results

Recovery of cellulose-rich pulp and preparation of waste-derived nanocellulose

The pretreatment process effectively converted sugarcane bagasse into cellulose-rich pulp. After alkaline treatment and hydrogen peroxide bleaching, the biomass changed from brown fibrous powder to a pale cellulose-rich pulp, indicating progressive removal of lignin-rich and hemicellulosic fractions. The cellulose content increased from 42.6% ± 1.8% in raw bagasse to 78.6% ± 2.4% in bleached pulp, w...

Discussion

This study demonstrates that waste-derived nanocellulose can serve as a structurally viable platform for constructing multifunctional aerogels with antibacterial, catalytic, and adsorption functions. The value of this design lies not only in converting sugarcane bagasse into a porous material, but also in using the nanocellulose network as a carrier for chitosan reinforcement and green AgNP immobilization. Recent reviews have emphasized that nanocellulose-based materials are attractive for water-pollutant removal because...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
100 µm nylon mesh	Commercial laboratory supplier		Used to filter chitosan solution before aerogel fabrication.
Acetic acid	Sigma-Aldrich	695092
Antibiotic disc positive control	Thermo Fisher	https://www.thermofisher.com/search/browse/category/us/en/90222069	Select according to the bacterial strain and local antibacterial testing standard.
BET surface area and porosity	Micromeritics ASAP 2460	ASAP 2460	Micromeritics describes the ASAP 2460 as a surface area and porosimetry analyzer with expandable high-throughput ports.
Calcium chloride	Sigma-Aldrich	946664	Report hydrate state according to the purchased reagent.
Carbon-coated copper TEM grids	Ted Pella	https://www.tedpella.com/grids_html/	Use actual grid specification in final table.
CasaXPS version reference	CasaXPS 2.3.25 or current installed version	https://casaxps.com/
Chitosan	Sigma-Aldrich	448869
Cylindrical polypropylene molds	Commercial laboratory supplier		Used for aerogel monolith molding.
Data analysis and plotting	OriginPro 2024
Escherichia coli	ATCC	ATCC 25922
Ethanol	Sigma-Aldrich	459844
Folin–Ciocalteu reagent	Sigma-Aldrich	F9252
Freeze dryer	Labconco FreeZone	https://www.labconco.com/category/freeze-dry-evaporation/freeze-dry-systems
FTIR	Thermo Scientific Nicolet iS50	912A0760	FTIR Spectrometer or equivalent
Gallic acid	Sigma-Aldrich	G7384	Use as calibration standard for Folin–Ciocalteu assay; product source should be checked against the lab’s actual purchase record.
Green tea leaves	Local supplier	Local supplier	Use batch record, brand, collection/purchase date, and total phenolic standardization instead of only a commercial webpage.
Hydrochloric acid	Sigma-Aldrich	258148
Hydrogen peroxide	Sigma-Aldrich	386790
ICP-OES	Agilent 5110	5110	PerkinElmer Avio 500 / equivalent
Image analysis	ImageJ 1.54	ImageJ/Fiji version should be reported according to the actual software package installed in the laboratory.
LB broth and LB agar	Thermo Fisher	10855001	Use actual supplier and catalog number from microbiology lab inventory.
Lead nitrate	Sigma-Aldrich	NIST928
Magnesium chloride	Sigma-Aldrich	M8266	Report hydrate state according to the purchased reagent.
Methylene blue	Sigma-Aldrich	M9140
Nitric acid	Sigma-Aldrich	438073	Use trace-metal grade if available for ICP-OES workflows.
PBS	Thermofisher Scientific	https://www.thermofisher.com/order/catalog/product/10010023	Used as antibacterial assay control/dilution medium.
Ready-to-use E. coli QC organism	Thermo Fisher Culti-Loops	Cat. No. R4607050	Alternative format for ATCC 25922
SEM	Hitachi SU8010 / ZEISS Sigma / equivalent	https://www.hitachi-hightech.com/global/en/products/microscopes/sem-tem-stem/sem/
Silver nitrate	Sigma-Aldrich	209139
Sodium borohydride	Sigma-Aldrich	452882	Sigma-Aldrich lists sodium borohydride 452882 as powder, ≥98.0%.
Sodium carbonate	Sigma-Aldrich	223530
Sodium chloride	Sigma-Aldrich	S9888
Sodium hydroxide	Sigma-Aldrich	221465
Staphylococcus aureus	ATCC	ATCC 25923	ATCC identifies S. aureus 25923 as a quality-control strain used for CLSI disk diffusion and media testing.
Prism 10	GraphPad	Version 10	Statistical analysis
Sterile filter-paper discs	Whatman		Used for disc-diffusion controls and aerogel-disc comparison.
Sugarcane bagasse	Local supplier	Local juice-processing source	Use collection record rather than supplier webpage; report location, date, drying method, and storage condition.
Syringe filters	Millipore	https://www.merckmillipore.com/US/en/products/filtration/laboratory-syringe-filters/syringe-filters	Match membrane material to solvent system and actual purchase record.
TEM	JEOL JEM-2100	JEM-2100
TGA	TA Instruments Q500	Q500
Universal testing machine	Instron 5943	5943
UV–Vis spectroscopy	Shimadzu	UV-2600i Plus
XPS data processing	CasaXPS	https://casaxps.com/
XRD	Bruker D8 Advance	https://www.bruker.com/en/products-and-solutions/diffractometers-and-x-ray-microscopes/x-ray-diffractometers.html	Rigaku SmartLab / equivalent