Poly(ammonium/ pyridinium)-chitosan Schiff base as a smart biosorbent for scavenging of Cu2+ ions from aqueous effluents

Chitosan Schiff bases (CSBs) decorated with ammonium or pyridinium motifs for recyclable biosorption of Cu²⁺ ions from aqueous effluents were tailored by grafting of salicylaldehyde ionic liquids (Sal-ILs) onto chitosan surface. Biosorption capacity of poly(ionic-salicylidene) CSBs (PISCSB_1,2) was compared with chitosan and poly(neural-salicylidene) CSBs (PSCSB). The ionic salicylidene-functionalized chitosan, poly(pyridinium)-salicylidene chitosan Schiff base (PISCSB₂), exhibited excellent adsorption capacity (99.1%), in comparison to chitosan (85%) and PSCSB (95%). Biosorption of Cu²⁺ ions onto PSCSB followed pseudo-first-order kinetic model while onto chitosan (CS) and PISCSB_1,2 followed pseudo-second-order kinetic model. However, Cu²⁺ ions biosorption onto all biosorbents fitted Langmuir adsorption isotherm model. Negative values of ΔG^o and ΔH^o confirmed the spontaneity and exothermic behavior of adsorption process. The new biosorbents could be successfully regenerated in aqueous 0.01 M EDTA solution with negligible loss in their adsorption capacity. Consequently, our new chitosan-based biosorbents may offer promising green and renewable scavengers for Cu²⁺ ions from wastewater.