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 (pHPZC) 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 π–π 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.