Synthesis of ZIF-8/chitosan composites for Cu²⁺ removal from water

In this work, a kind of novel Chitosan (Cs)-doped zeolite imidazole framework (ZIF-8@Cs) with a larger surface area and a smaller pore size was synthesised via a facial solvothermal approach and applied to remove Cu²⁺ from mine wastewater. Compared to nondoped ZIF-8, ZIF-8@Cs exhibited a stronger adsorption performance and removal efficiency. The reason was that ZIF-8@Cs doped by the Cs could suppress the aggregation and increase the monodispersity of ZIF-8. Using the high-performance ZIF-8@Cs, as a novel adsorbent, was successfully developed for the efficient removal of Cu²⁺ from mine wastewater. Various parameters, such as contact time, initial Cu²⁺ concentration, adsorbent dosage, and pH, were investigated. The results showed that a removal efficiency of 85% was obtained at 4 h contact time for a Cu²⁺ concentration of 30 mg/L at the optimum pH of 6.0. Equilibrium data were analysed using different isothermal models and kinetic models, analytic results indicated that the capture of Cu²⁺ by ZIF-8@Cs could favourably comply with the pseudo-first-order kinetic model and Langmuir isotherm model. The single-layer adsorption of Cu²⁺ on ZIF-8@Cs was dominated by diffusional mass transfer. Additionally, the results of the thermodynamic analysis indicated that the adsorption of Cu²⁺ by ZIF-8/Cs was a spontaneous, exothermic, and ordered process. Overall, the results reported herein indicated that ZIF-8/Cs with high adsorption efficiency are very attractive and imply a potential practical application for the removal of potentially toxic elements in wastewater.