Cold Plasma-Engineered CNPs/TiO2 /CuO/Chitosan Nanocomposite for Cadmium Adsorption: Optimization, Isotherms, Kinetics, and Selectivity

This study reports the fabrication of a cold plasma–engineered CNPs/TiO 2 /CuO/Chitosan nanocomposite for effectively sequestering cadmium (Cd(II)) ions from aqueous media. The green cold-plasma synthesis approach simultaneously integrated multiple functional groups onto carbon nanoparticles (CNPs), generating a highly active heterogeneous surface. Applied to the ternary TiO 2 /CuO/Chitosan system, the nanocomposite delivered superior adsorption performance. Response surface methodology (RSM) optimized key process parameters: initial Cd(II) concentration at 68.62 mg L -1 , nanocomposite dosage at 26.20 mg, pH 6.89, and contact time of 79 min. Analysis of variance (ANOVA) confirmed the statistical significance of these variables and their interactions. Under these optimized conditions, the nanocomposite achieved a 91.98% adsorption efficiency. Kinetic analysis followed a pseudo-second-order mechanism, while isotherm data aligned well with the Freundlich model, suggesting multilayer adsorption. The nanocomposite’s selectivity in binary systems containing Pb(II) ions was also evaluated. In single-component systems, equilibrium capacities reached 120.45 mg g -1 and 99.75 mg g -1 for Cd(II) and Pb(II), respectively. In binary matrices, these capacities decreased to 85.65 mg g -1 and 50.35 mg g -1 , and the selectivity coefficient (αCd/Pb) peaked at 4.58 (pH 6.5). Reusability studies confirmed the nanocomposite’s structural and chemical stability, retaining 87.25% of its adsorption efficiency after five successive acidic desorption cycles. These findings demonstrate that the cold plasma-engineered CNPs/TiO 2 /CuO/Chitosan nanocomposite is a robust, efficient, and environmentally friendly candidate for sustainable wastewater treatment applications.