Synthesis, characterization, and application of ZIF-8 for removal of Cd, Ni, and Pb ions from aqueous solutions: Optimization of the process by Response Surface Methodology (RSM) based on Central Composite Design (CCD) technique

A Zeolitic imidazolate framework-8 (ZIF-8) was synthesized by the solvothermal method of zinc nitrate hexahydrate and 2-methylimidazole in DMF to remove Cd(II), Ni(II), and Pb(II) ions from aqueous solutions. The synthesized ZIF-8 was distinguished by XRD, FT-IR, BET, SEM, EDX, TEM methods. Several significant variables were optimized with response surface methodology (RSM) to obtain the highest removal of metal ions. According to the achieved results, the aqueous solution pH values of 6.5, 6.5, and 6.0, ZIF-8 dosages of 0.05, 0.06, and 0.05 g⸳L-1, and metal ions initial concentrations of 50, 60, and 60 mg⸳L-1 were chosen as the optimum amount of these variables for Cd(II), Ni(II), and Pb(II) ions adsorption from solution, respectively. The equilibrium time for metal ions adsorption was found at 50 min. Three-dimensional plots demonstrate relationships between the metal ion uptakes with the paired factors, which illustrate the behavior of the sorption system in a batch process. Based on the experimental results and model parameters, maximum adsorption efficiencies were achieved 89.76, 72 and 68.43% for Cd(II), Ni(II) and Pb(II), respectively. It can be suggested that the synthetized ZIF-8 has excellent potential as an effective adsorbent and used for heavy metal sorption from water environment.