Optimization of facile synthesis of xanthan gum xanthate based hydrogel for the capturing of heavy metal ions from aqueous solutions.

This study investigated the elimination of Co, Ni and Cu ions from water using a mesoporous, cost-effective, reusable, biodegradable and efficient xanthan gum xanthate-based hydrogel (XGmXHs hydrogel) as an adsorbent. The XGmXHs hydrogel was prepared via free radical polymerization process with varying the ratios of 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) as monomers. These ratios were optimized based on grafting efficiency, swelling capacity and point of zero charge (ΔpH) analysis. The results demonstrate that the XGmXHs hydrogel containing copolymer of HEMA: AA in a 1:3 ratio is optimal for grafting on xanthan gum (XGm) during polymerization process. The 1:3 ratio of monomer grafted on xanthan gum xanthate (XGmX) is referred to as XGmXHs-3 hydrogel. The XGmXHs-3 hydrogel showed a consistently negative surface charge across a diverse pH range, resulting the AA content was enhanced. Consequently, the swelling and adsorption capacity of the XGmXHs-3 hydrogel is significantly high. The optimum swelling capacity of the XGmXHs-3 hydrogel was found 40,128 % in water at pH 11. The maximum removal efficiency was 92.21 % for Co, 95.45 % for Ni and 98.30 % for Cu ions at pH 7. According to isothermal studies, the adsorption data aligns most closely with Langmuir isotherm model, resulting the adsorption capacities of 358.42, 469.48 and 555.55 mg/g Co, Ni and Cu ions, respectively. The adsorption kinetics were consistent with a pseudo-first-order kinetic model, showing rate constant of -2.6 × 10, -4.0 × 10 and - 6.3 × 10 min for Co, Ni and Cu ions, respectively. The desorption efficiencies were 64.76 % for Co, 68.83 % for Ni and 72.11 % for Cu ions to the XGmXHs-3 hydrogel after being regenerated for the fifth cycle.