Mesoporous Crosslinked Chitosan-Activated Charcoal Composite for the Removal of Thionine Cationic Dye: Comprehensive Adsorption and Mechanism Study

Chitosan (CS) was coalesced with activated charcoal (AC), followed by crosslinking reaction with epichlorohydrin (ECH) to form a mesoporous crosslinked chitosan-epichlorohydrin/activated charcoal composite (CS-ECH/AC). The structural and physicochemical properties of CS-ECH/AC were characterized by Brunauer-Emmett-Teller, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and point-of-zero charge (pH(PZC)) analyses. CS-ECH/AC was used to remove thionine (TH), a model cationic dye, from aqueous solution. Batch mode adsorption studies were performed by varying operational adsorption parameters, such as adsorbent dosage (0.04-0.30 g), solution pH (3-11), initial TH dye concentrations (10-100 mg/L), and contact time (0-270 min). The equilibrium data was described well by the Freundlich isotherm, and the maximum adsorption capacity of CS-ECH/AC for TH dye adsorption was 60.9 mg/g at 303 K. The kinetic uptake profiles were well described by the pseudo-second-order model. Thermodynamics results indicated a spontaneous and exothermic adsorption process. The proposed adsorption mechanism included mostly electrostatic attractions, H-bonding interactions, and pi-pi interactions. All these results showed that CS-ECH/AC can be considered as a feasible biocomposite material for the removal of cationic dyes from wastewater.