High-efficiency Cr(VI) decontamination using glutaraldehyde-crosslinked chitosan/biochar composites: Performance optimization and mechanistic insights

Abstract

Industrial effluents containing Cr(VI) pose a severe threat to the natural environment and human health. To address this challenge, glutaraldehyde-crosslinked chitosan-modified biochars (GA-CSBB and GA-CSRB) were fabricated via a facile synthesis route, uniquely employing glutaraldehyde as a crosslinker to enhance chitosan loading and adsorption capacity. SEM/BET analyses demonstrated rougher surfaces and enlarged pores in GA-CSBB/GA-CSRB, enhancing active site accessibility. Additionally, a greater abundance of surface functional groups significantly facilitated the adsorption process. Adsorption follows Langmuir isotherm and pseudo-second-order kinetics, indicating chemisorption-controlled monolayer adsorption. Maximum Langmuir capacities reach 123.5 and 144.3 mg/g for GA-CSBB and GA-CSRB, aligning closely with experimental results (131.8 and 140.2 mg/g). At optimal conditions (25 °C, pH 2, 40 mg/L initial Cr(VI)), GA-CSBB and GA-CSRB achieve 20.1 and 20.9 mg/g adsorption capacities, corresponding to complete/near-complete removal (100 % and 99.1 %). Remarkably, both adsorbents retain > 86 % removal efficiency across pH 2–8 and in the presence of competitive anions (Cl^-, NO₃^-, SO₄^2-, PO₄^3-). By comparison, pristine biochars (BB, RB) and non-crosslinked chitosan-modified biochars (CS-BB, CS-RB) exhibit significantly lower capacities (9.0–12.8 mg/g). Comprehensive mechanistic analysis identified surface complexation, electrostatic interactions, redox reactions, and chelation mechanisms as key contributors to the removal process. In summary, this study presents a facile, eco-friendly, and highly efficient adsorbent, offering a promising strategy for the effective treatment of Cr(VI)-laden wastewater.