Comparative Performance of Commercial Versus Biosynthesized Chitosan Epichlorohydrin/Kaolinite Biocomposites for Methyl Orange Removal: Box Behnken Optimization, Adsorption Mechanism, and Density Functional Theory Calculations

Abstract

Water contamination by synthetic dyes poses a serious environmental threat, driving the need for affordable and efficient adsorbents. This study developed two novel biocomposites by grafting commercial chitosan (c-CTS ECH/KC) and locally biosynthesized chitosan (b-CTS-ECH/KC) onto natural kaolinite clay from Algeria using epichlorohydrin as a crosslinking. Characterization via FTIR, BET, and EDX confirmed successful chitosan grafting and demonstrated an increase in surface area compared to raw kaolinite. Adsorption performance for methyl orange (MO) dye was optimized using response surface methodology, achieving maximum removal efficiencies of 82.6% and 80.2% for c-CTS-ECH/KC and b-CTS-ECH/KC, respectively. Kinetic studies revealed chemisorption as the rate limiting step, while equilibrium data fitted the Langmuir model for c-CTS-ECH/KC (qmax: 216.92 mg/g) and the Freundlich model for b-CTS-ECH/KC (qmax:204.082mg/g), indicating surface heterogeneity. Thermodynamic analysis showed the adsorption was spontaneous, endothermic, and entropy-driven. Computational DFT and NBO analyses supported the experimental findings, revealing enhanced surface reactivity upon chitosan modification and strong electrostatic interactions between chitosan's electron-rich amino groups and MO's sulfonate oxygens, alongside hydrogen bonding and π–π stacking. Overall, these chitosan-modified kaolinite biocomposites demonstrate significant promise as sustainable, cost-effective adsorbents for treating dye-contaminated wastewater.