Adsorptive performance of carbon modified chitosan biopolymer for cationic dye removal: kinetic, isotherm, thermodynamic, and mechanism study

Chitosan (CTS) biopolymer was modified by commercial activated charcoal (AC) as a source of carbon to fabricate a hybrid chitosan-activated charcoal (CTS-AC) composite biosorbent to remove thionine (TH), acationic dye, from aqueous solution. The key factors affecting adsorption process, i.e. CTS-AC mass (0.04–0.4 g), initial pH (4–11), initial dye concentrations (10–100 mg/L) and contact time (0–570 min) on TH removal efficiency were tested and optimised. The optimum conditions for TH removal were obtained at CTS-AC dosage = 0.16 g, solution pH = 10, and contact time = 60 min. The experimental data indicated that the adsorption process is in line with the pseudo-second-order (PSO) kinetic and the Freundlich isotherm models. The maximum adsorption capacity of 56.7 mg/g was recorded for CTS-AC composite at 303 K. The calculated thermodynamic functions show that the TH adsorption process was endothermic and spontaneous. Besides, the adsorption mechanism of TH onto the CTS-AC may include electrostatic interactions, hydrogen bonding, and π-π interactions. This study suggests that CTS-AC composite has a great potential as an eco-friendly and effective biosorbent for the removal of cationic dyes from aqueous environment.