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This study developed eco-friendly composite hydrogel based on cellulose and bentonite to remove Pb2+ from wastewater. The composite hydrogel adsorbents' morphology, chemical composition, and structure were characterized using FE-SEM, EDX, FT-IR, and XRD. Furthermore, EDX mapping displayed uniform dispersion of bentonite within the cellulose-based hydrogel (H), leading to enhanced swelling capacity and mechanical strength. To optimize the adsorption process, the effect of experimental conditions on the amount of Pb2+ adsorbed per bentonite/cellulose-based composite hydrogel (BCH3) was investigated. The batch adsorption results showed that the maximum adsorption capacity of Pb2+ onto BCH3 was 110.64 mg g-1. Post-adsorption EDX spectra and FTIR analysis provided evidence of successful Pb2+ uptake by BCH3. The results obtained from these analyses suggest that the primary adsorption mechanism involves the interaction of Pb2+ with nitrogen (NH2) and oxygen (COO-) groups on the BCH3 surface. Kinetics and isotherm data were best described by the pseudo-second-order (R2 = 0.999) and Sips models (R2 = 0.996). The kinetic model indicated that Pb2+ uptake onto the BCH3 was primarily governed by chemisorption involving coordination bonding/electrostatic interactions. The BCH3 adsorbent exhibited selectivity towards Pb2+ compared to Cd2+ and demonstrated good reusability after five adsorption-desorption cycles.

In this study, bentonite/amino-functionalized cellulose composite (BAC) adsorbent was synthesized by intercalating the hexadecyl trimethyl ammonium bromide surfactant (HDTMA) into bentonite followed by exfoliating the HDTMA-modified bentonite (MB) into amino-functionalized cellulose (AC). The physicochemical properties of BAC were evaluated by FTIR, XRD, FE-SEM, EDX, TGA, and Zeta potential measurement. A series of batch mode adsorption experiments were carried out to identify the optimal adsorption conditions as a function of experimental variables such as pH of solution, uptake time, initial Pb2+ concentrations, BAC dosage, and assess both percent removal (%) and Pb2+ uptake (mg g−1). The result demonstrated that the synergetic advantage of combining HDTMA-modified bentonite (MB) and amino-functionalized cellulose (AC) in Pb2+ uptake (69 mg g−1) surpassed that of HDTMA-modified bentonite (12.14 mg g−1) and amino-functionalized cellulose (31.33 mg g−1) alone. Further, Pb2+ uptake onto BAC was higher than the HDTMA-modified bentonite/cellulose composite (BC) (42.12 mg g−1) due to the introduction of the amino group to cellulose through grafting with ethylenediamine (EDA). The adsorption of Pb2+ from aqueous solution by BAC fit well with pseudo - 2nd-order kinetic (R2 = 0.998) and Langmuir isotherm (R2 = 0.999) models. The kinetic study indicated that the active sites in the BAC exhibit heterogeneity and possess different activation energies for chemisorption. The monolayer attachment of Pb2+ onto the BAC surface was realized from the isotherm study, and the maximum predicted adsorption capacity was found to be 71.869 mg g−1. Regeneration studies showed that BAC maintained its good Pb2+ uptake capacity for up to four cycles.

Water pollution, driven by Pb2+, poses a significant threat to biotics and the environment. A promising solution to address the issue is the utilization of cellulose from lignocellulosic materials as an adsorbent to remove or reduce Pb2+ from wastewater. However, as reported, the adsorption capacities of native cellulose adsorbents vary depending on their plant source, and their metal binding capacity is not as satisfactory as expected due to a lack of robust chelation sites, particularly amino groups. Thus, this study aimed to improve Pb2+ uptake capacity by utilizing the prosopis juliflora stem, a previously unexplored cellulose source, as an adsorbent through ethylenediamine (EDA) grafting. FTIR, XRD, FE-SEM, EDX, and TGA evaluated the physicochemical properties of amino-decorated cellulose (ADC) adsorbent. The effect of experimental variables (initial Pb2+ concentration, ADC dose, and contact time) on percent removal was investigated and analyzed using Box-Behnken Design (BBD). Analysis of variance (ANOVA) revealed that, among the interaction effects, only the interactions between initial Pb2+ concentration and ADC dose significantly affected percent removal (P