Synthesis of zeolitic imidazolate framework-8 (ZIF-8) using different solvents for lead and cadmium adsorption

The current study is focused on the facile synthesis of zeolitic imidazolate framework-8 (ZIF-8) at room temperature using three different solvents: ammonia solution (ZIF-8 (N)), aqueous solution (ZIF-8 (H)), and methanol (ZIF-8 (M)). The ZIF-8s produced have high crystallinity with different sizes and shapes. The morphology of ZIF-8 (H) resembled the mixture of cubic and the rhombic dodecahedron with truncated corners, whereas ZIF-8(M) occurred as the most stable rhombic dodecahedron, and ZIF-8(N) appeared as cubes with truncated corners. ZIF-8 (N) had the largest average particle size of 573 nm, followed by ZIF-8 (H) and ZIF-8 (M) with average sizes of 108 nm and 62 nm, respectively. ZIF-8 (N) showed a rapid Pb(II) and Cd(II) adsorption, within 15 min, while ZIF-8(H) achieved Pb(II) and Cd(II) equilibrium within 240 min, and 300 min for ZIF-8 (M). The adsorption of Pb(II) and Cd(II) is best fitted with the Langmuir isotherm and pseudo-second-order kinetic model. The maximum adsorption capacities for Pb(II) and Cd(II) sorption were 454.55 and 312.50 mg/g for ZIF-8 (H), 434.78 and 277.78 mg/g for ZIF-8 (M), respectively, and 476.19 and 263.16 mg/g for ZIF-8 (N), respectively. All of the prepared ZIF-8s showed a promising competency as adsorbents for the removal of Pb(II) and Cd(II) from an aqueous solution.