Box–Behnken Design for Optimizing Synthesis and Adsorption Conditions of Covalently Crosslinked Chitosan/Coal Fly Ash Composite for Reactive Red 120 Dye Removal

In this research, a biocomposite adsorbent of covalently crosslinked chitosan-epichlorohydrin/coal fly ash (CHT-ECH/CFA) was synthesized and applied for reactive red 120 dye (RR120) removal. The CHT-ECH/CFA was characterized by BET, pH potentiometric, pH pzc , XRD, FTIR and SEM-EDX. A statistical optimization by Box–Behnken Design (BBD) was employed to assess the effects of the adsorption key parameters such as CFA loading into CTH-ECH matrix, adsorbent dose, solution pH, working temperature and contact time. The optimized CFA loading, adsorbent dose, temperature, time, and pH were observed to be 50%, 0.07 g, 45 °C, 60 min, and solution pH 4 respectively. From BBD, the highest removal of RR120 at optimum operation conditions was found to be 90.2%. The experimental results show the adsorption process can be perfectly described by both Langmuir and Freundlich isotherm models with maximum adsorption capacity of 237.7 mg/g at 45 °C. Moreover, the adsorption kinetics were well fitted to the pseudo-second order model. This research introduces a new hybrid biocomposite adsorbent with potential application for the treatment of anionic dye-polluted water.