Modular Cross-Linked Chitosan Beads with Calcium Doping for Enhanced Adsorptive Uptake of Organophosphate Anions

Chitosan beads were cross-linked at variable composition with glutaraldehyde (GA) and epichlorohydrin (EP), respectively. The beads were post-treated by impregnation with a CaCl 2 solution and characterized to evaluate the structure and physicochemical effect of calcium doping. The bead adsorption properties were studied at pH 8.5 with p -nitrophenyl phosphate (PNPP), where beads cross-linked with GA showed higher uptake relative to beads cross-linked with EP. Calcium doping of GA beads showed a 4-fold greater uptake (0.97 mmol g –1 ) over non-cross-linked (NCL) beads (0.23 mmol g –1 ). By comparison, EP-based beads with calcium doping showed a 2-fold enhancement for the uptake of PNPP (0.90 mmol g –1 ) over NCL beads. This work illustrates the utility of cross-linking and calcium doping as modular strategies for tuning the adsorption behavior of chitosan-based beads. Calcium-doped beads cross-linked with glutaraldehyde showed favorable adsorption–desorption properties where the uptake capacity of PNPP remained relatively constant (19.6–17.5%) over several regeneration cycles. The results of this work contribute significantly to the development of advanced materials for the controlled uptake and treatment of waterborne phosphate species.