Polyvinyl alcohol modified chitosan composite as a novel and efficient adsorbent for multi-metal removal

This study focussed on the development of a novel and efficient adsorbent derived from polyvinyl alcohol-modified chitosan composite for the removal of Cu+2, Ni+2, and Zn+2 from wastewater. The characterization of composite exhibits mesoporous, thermal stability, and rich with functional groups. The Box-Behnken method of Response Surface Methodology framework was employed, and attained optimum conditions for Cu+2 (1000 mg/l, 20 min, 1 g/l), Ni+2 (1000 mg/l, 20 min,1 g/l), and Zn+2 (972.28 mg/, 20 min, 1 g/l) respectively. Langmuir isotherm and Pseudo-Second order kinetic model best fit, indicating chemisorption-driven monolayer adsorption and achieved maximum adsorption capacity 303.29 mg/g, 209.08 mg/g, and 173.39 mg/g for Cu+2, Ni+2, and Zn+2 respectively. In competitive adsorption of binary and ternary systems, Cu+2 displayed superior removal efficiency compared to Ni+2 and Zn+2. Furthermore, the adsorbent's efficacy was evaluated using industrial effluent, demonstrating higher removal efficiency for Cu+2 (79.09 %) compared to Ni+2 (50.73 %) and Zn+2 (46.97 %). Thermodynamic study (Enthalpy: 19.08 to 26.29 kJ mol−1, Gibb’s free energy: −0.32 to − 3.10 kJmol−1, Entropy: 65.10 to 90.95 J mol−1 K−1) underlined the spontaneity and endothermic nature of adsorption. The desorption efficiency ranging from 88.94 % to 48.90 %, 88.19 % to 41.31 %, and 84.09 % to 48.19 % up to 10th cycles for Cu+2, Ni+2, and Zn+2 using 0.4 mol/l H2SO4, 0.6 mol/l HNO3, and 0.6 mol/l HCl respectively. The adsorption mechanisms, primarily surface complexation, ion exchange, and electrostatic attraction, prevail over physisorption. The PVA-CS, recognized as highly efficient and environment friendly adsorbent provides a practical solution for water decontamination.