Preparation of Hybrid β-Chitosan – Squid Pen Protein Hydrogel Beads by Ionic Liquid Regeneration for Adsorption of Copper (II) and Zinc (II) from Wastewater

This study explores the use of squid pen protein to enhance the mechanical properties, chemical stability, and heavy metal ion (Cu2+ and Zn2+) affinity of β-chitosan. 1-Butyl-3-methylimidazilium acetate ([BMIM][OAc]) was used to functionalize β-chitosan and prepare hydrogel beads with improved structural integrity and batch uniformity. However, initial experiments noted a reduction in adsorption capacity as the squid pen protein content increased, with Cu2+ and Zn2+ adsorption being particularly inhibited at lower pH levels due to protonation. Subsequent batch adsorption studies identified optimal conditions for Cu2+ and Zn2+ uptake and revealed that adsorption followed pseudo-second-order kinetics, indicating chemisorption. The equilibrium isotherms corresponded with the Langmuir model, suggesting monolayer coverage with maximum adsorption capacities of 70.2 mg g-1 for Cu2+ and 24.0 mg g-1 for Zn2+. The potential of squid pen protein as an economical filler for β-chitosan-based adsorbents was validated alongside the efficiency of using [BMIM][OAc] for the non-toxic functionalization of β-chitosan. Support of green chemistry principles was evidenced by a high atom economy and low environmental impact, indicating a sustainable method for preparing effective biosorbents.