Chitosan-Based Biocomposite Hydrogels with Squid Pen Protein for Anionic Dyes Adsorption

Abstract

Growing environmental concerns have driven the search for sustainable wastewater treatment solutions, particularly for the removal of persistent synthetic dyes. This study explores hydrogels made from squid pen protein (SPP) and chitosan, biodegradable polymers, for anionic dye adsorption─reactive blue 4 (RB4) and methyl orange (MO). A 50%/50% SPP/chitosan hydrogel was optimal for RB4 adsorption while minimizing chitosan use. Adsorption followed the Langmuir model, with capacities of 151.52 mg/g for RB4 and 54.94 mg/g for MO. Optimal RB4 adsorption conditions were 65 °C, 6 h, pH 7, and 0.2 wt % adsorbent at 300 rpm. Kinetic analysis indicated a pseudo-second-order model, suggesting chemisorption. Characterization (Fourier Transform Infrared Spectroscopy - FT-IR, Scanning Electron Microscopy - SEM, X-ray Photoelectron Spectroscopy - XPS) revealed functional groups and binding mechanisms, with XPS confirming a nucleophilic attack from the between amino groups of chitosan/SPP protein and the dichlorotriazine moiety of RB4. Higher cross-linker content reduced adsorption. This study demonstrates SPP/chitosan hydrogels as a cost-effective and sustainable alternative for wastewater treatment.