Synthesis of a highly porous three-dimensional PVA/GO/ZIF-67 cryogel for the simultaneous treatment of water contaminated with cadmium(ii) and lead(ii) heavy metal ions

Abstract

In this research, the PVA/GO/ZIF-67 cryogel as a highly porous three-dimensional polymeric adsorbent was synthesized via a freeze-drying method and applied for the simultaneous removal of Cd²⁺ and Pb²⁺ ions from contaminated water samples. Characterization of the as-prepared cryogel was carried out via XRD, FTIR, FESEM-EDX, and zeta potential analysis. The influence of variables on the adsorption process was assessed under experiments with a central composite design, and the optimum values were determined for the pH of the solution (6.5), the initial Pb²⁺ concentration (10 mg L⁻¹), the initial Cd²⁺ concentration (10 mg L⁻¹), the adsorbent dosage (12 mg), and the contact time (35 min). Also, four isotherm models were applied for evaluation of the experimental data, and the results illustrated good fitting of the data by the Langmuir isotherm model, with the maximum adsorption capacities of 106.8 mg g⁻¹ and 93.79 mg g⁻¹ for Pb²⁺ and Cd²⁺, respectively. In addition, the pseudo-second-order kinetic model (R² = 0.999) was fitted better than other kinetic models for both of the contaminants. Thermodynamic studies confirmed that the process of adsorption was endothermic and spontaneous. Finally, the cryogel showed great performance in regeneration studies and real water sample testing, and can be presented as a potential adsorbent for the removal of heavy metal ions from wastewater.