Chitosan-based adsorptive membrane modified by carboxymethyl cellulose for heavy metal ion adsorption: Experimental and density functional theory investigations

Abstract

Low adsorption capacity and weak mechanical stability are the main drawbacks of chitosan (CS)-based adsorptive membranes for heavy metal ion removal. Polyvinyl alcohol (PVA) has been used to improve the mechanical stability of CS membranes, but adsorption capacity is disregarded. In the current study, the surface of the chitosan/polyvinyl alcohol (CP) membrane was modified using carboxymethyl cellulose (CMC) to increase its heavy metal ion adsorption capacity. Experimental and density functional theory (DFT) calculations were used to evaluate the heavy metal ion (As³⁺ and Cr³⁺) adsorption capabilities of CP and carboxymethyl cellulose-functionalized CP (CMC-CP) membranes. The batch adsorption process presented a higher heavy metal adsorption capacity of the CMC-CP membrane (As³⁺/CMC-CP = 234.78 mg/g and Cr³⁺/CMC-CP = 230.12 mg/g) compared to the CP membrane (As³⁺/CP = 89.02 mg/g and Cr³⁺/CP = 75.61 mg/g). The heavy metal/CMC-CP complexes confirmed higher adsorption energies (As³⁺/CMC-CP = -23.62 kcal/mol and Cr³⁺/CMC-CP = -23.21 kcal/mol) than the heavy metal/CP complexes (As³⁺/CP = -3.47 kcal/mol and Cr³⁺/CP = -2.92 kcal/mol). The electronic band structure was higher for CMC-CP (5.42 eV) compared to CP (4.43 eV). Experimental and theoretical findings were close, implying that the CMC-CP membrane has superior heavy metal adsorption capability than the CP membrane.

Keywords: Adsorption; Carboxymethyl cellulose; Chitosan membrane.