Xanthate-modified chitin hydrogel for enhanced Cu ²⁺ and Co ²⁺ metal ions removal: Kinetic and regeneration studies

A Chitin-based hydrogel (Ch-X@ACN) was produced by free radical polymerization, employing acrylic acid and cyclohexyl methacrylate monomers. The prepared hydrogel was characterized via Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric (TG) analysis, point of zero charge (ΔpHPZC), and scanning electron microscopy (SEM). The swelling and water retention behavior of Ch-X@ACN-2 hydrogel in distilled, tap and grey water were investigated under optimized conditions, maximum swelling capacity of 312.34 (±14.35) g/g in distilled water and a water retention ratio of 79.99 (±1.72) in grey water within 24 h. Adsorption studies demonstrated the hydrogel’s high affinity toward Cu2+ and Co2+ ions from aqueous media, the maximum removal of 95.10 (±2.85) % for Cu2+ and 90.35 (±2.71) % for Co2+ at pH 7. The adsorption equilibrium data fits well to Langmuir isotherm model, achieving maximum adsorption capacities of 549.02 (±25.40) mg/g for Cu2+ and 538.97 (±18.3) mg/g for Co2+. Kinetic studies indicated that adsorption followed pseudo-second-order model suggesting chemisorption. Thermodynamic parameters confirmed spontaneity (ΔG < 0) and endothermic nature (ΔH > 0). This hydrogel Ch-X@ACN-2 exhibited good reusability, maintaining desorption efficiencies of 86.76% for Cu2+ and 84.85% for Co2+ in fifth regeneration cycle. These results establish the chitin-based hydrogel as relatively cheap, eco-friendly, and have strong tendency to adsorb metal ions.