Enhanced lead (II) adsorption from aqueous solution using sawdust-derived amino-decorated cellulose: Optimization, isotherm, kinetics, and reusability studies

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 < 0.0008). The optimal percent removal and Pb2+ uptake onto ADC at conditions: pH of 5, ADC dose of 0.47 g, initial Pb2+ concentration of 52 mg L-1, and contact time of 118 min was 97.37 % and 53.86 mg g(-1), respectively. The uptake of Pb2+ onto ADC agreed well with the Langmuir isotherm and the pseudo-second-order kinetic model. The adsorption isotherm analysis demonstrated that ADC created a monolayer for Pb2+ attachment during adsorption, with a maximum Langmuir Pb2+ uptake capacity of 64.72 mg g(-1). Additionally, the analysis of the adsorption kinetics indicated that chemisorption was the dominant mechanism for the removal of Pb2+. Results from regeneration studies revealed that ADC retained its good Pb2+ uptake capacity for up to four cycles.