mSiO₂@Chitosan-derived carbon hybrid for efficient removal of cationic dyes from aqueous solutions: kinetic,...

A mesoporous SiO₂@chitosan-derived carbon hybrid (mSiO₂@CT-derived carbon hybrid) was synthesized via a silica-assisted carbonization strategy and evaluated as an efficient adsorbent for the removal of the cationic dyes methylene blue (MB) and crystal violet (CV) from aqueous solutions. Incorporation of mesoporous silica significantly improved the structural properties of the carbon hybrid by increasing its specific surface area, pore accessibility, and the availability of adsorption-active sites compared with pristine chitosan (CT) and the mSiO₂@CT composite. The adsorption performance was systematically investigated by evaluating the effects of solution pH, contact time, initial dye concentration, and temperature. Under the optimum conditions, the mSiO₂@CT-derived carbon hybrid exhibited maximum Langmuir adsorption capacities of 240 mg g^-1 for MB and 215 mg g^-1 for CV. Kinetic analysis indicated that adsorption was predominantly described by the pseudo-first-order model, whereas CV adsorption onto the mSiO₂@CT-derived carbon hybrid was better represented by the pseudo-second-order model. The equilibrium data were well fitted by the Langmuir isotherm, indicating monolayer adsorption on homogeneous adsorption sites. Furthermore, the Dubinin-Radushkevich and Temkin models suggested that chemisorption played a dominant role in the adsorption process, with adsorption energies ranging from 28.87 to 34.10 kJ mol^-1. Thermodynamic analysis confirmed that the adsorption process was spontaneous for all adsorbents, while the mSiO₂@CT-derived carbon hybrid exhibited favorable endothermic adsorption accompanied by increased randomness at the solid-liquid interface. These findings demonstrate that the synthesized mSiO₂@CT-derived carbon hybrid is a sustainable, environmentally friendly, and cost-effective adsorbent with considerable potential for the efficient removal of cationic dyes from contaminated wastewater.