Porous bioactive chitosan-based catalyst via UV-grafting ice-templated and self-reduction approaches for effective hydrogenation reduction of azo dye

Abstract

Bio-based porous materials have attracted significant attention over recent decades as environmentally sustainable alternatives to synthetic counterparts. This study synthesized a three-dimensional porous biocatalyst through UV-assisted cryopolymerization to graft acrylamide onto chitosan chains, followed by in situ integration of silver nanoparticles via a self-reduction mechanism. The composite exhibited enhanced antibacterial efficacy against Escherichia coli (E. coli), attributable to the synergistic effects of chitosan and silver nanoparticles. A rapid swelling ratio (20 s) corroborated the macroporous architecture of the material. The biocatalyst demonstrated exceptional catalytic performance in the hydrogenation reduction of Congo red azo dye under both deionized and tap water conditions when paired with a reducing agent. Notably, formulations with lower chitosan content achieved superior reduction kinetics, yielding apparent rate constants of 0.160 min⁻¹ and 0.117 min⁻¹ in deionized water and tap water, respectively. Key structural advantages such as tunable porosity, hydrophilicity, biodegradability, and an economical fabrication protocol collectively contributed to its enhanced catalytic efficiency. Critical operational parameters such as biocatalyst dosage and temperature were systematically evaluated to assess scalability potential. Thermodynamic analysis via the Arrhenius equation revealed an activation energy (Eₐ) of 35.45 kJ.mol⁻¹ for Congo red hydrogenation. Complementary Eyring equation calculations provided enthalpy (ΔH = −33.67 kJ.mol⁻¹) and entropy (ΔS = −159.15 J.mol⁻¹.K⁻¹), consistent with an associative reaction mechanism. The biocatalyst maintained robust reusability over four consecutive cycles with negligible change in hydrogenation reduction performance. Collectively, this work establishes a green, high-performance biocatalytic platform with superior environmental compatibility compared to conventional synthetic catalysts, underscoring its potential for sustainable wastewater treatment applications.