Synthesis and functionalization of a Chitosan-PEI-Metallothionein biopolymer with enhanced mechanical and adsorptive properties for heavy metal removal

Abstract

A novel biofunctionalized polymeric adsorbent, Chitosan-Polyethyleneimine-Metallothionein-like Proteins (Chitosan-PEI-MTLPs), was synthesized through a controlled multi-step grafting and immobilization strategy. Mechanical analysis revealed a substantial enhancement in mechanical integrity following PEI grafting and MTLP conjugation, with the flexural strength (FS) increasing from 25.48 MPa (chitosan) to 68.75 MPa (Chitosan-PEI-MTLPs), and compressive strength (CS) rising from 51.25 MPa to 129.35 MPa. Water absorption increased from 19.9% to 32%, indicating improved hydrophilicity and porosity. The synthesized biocomposite demonstrated exceptional adsorption performance for Cd(II), Ni(II), and Pb(II) ions, achieving maximum removal efficiencies of 93%, 89%, and 95%, respectively, at pH 6.5 and 45 °C. Kinetic studies confirmed a pseudo-first-order model, suggesting a predominantly physical adsorption process. Reusability tests demonstrated excellent regeneration capability, with 89–91% capacity retention after eleven cycles. These findings establish the Chitosan-PEI-MTLPs polymer as a highly stable, reusable, and biocompatible adsorbent with potential for selective heavy metal remediation in aqueous systems.