Effects of different solvents on the preparation of zeolitic imidazolate framework-8 (ZIF-8) for the removal of lead and cadmium

Abstract

The physicochemical properties of ZIF-8 is significantly affected by the choice of solvents during synthesis. Synthesis at room temperature of several zeolitic imidazolate framework-8s (ZIF-8s) using three different solvents: ammonia solution (ZIF-8 (N)), methanol (ZIF-8 (M)), and aqueous solution (ZIF-8 (H)) were explored. XRD and FTIR analyses showed that all ZIF-8s adsorbents obtained similar XRD peaks and FTIR spectra. The FESEM images showed that ammonia solution produced the biggest average particles size of 573.4 nm, followed by aqueous solution and methanol, with 108.92 nm and 61.86 nm, respectively. From the lead and cadmium adsorption test, ZIF-8 using methanol as solvent showed the least adsorption capacities as compared with ZIF-8 from aqueous and ammonia solution due to its higher degree of agglomeration. The maximum adsorption capacities for ZIF-8 using aqueous solution, methanol, and ammonia solution were 454.55, 434.78, and 476.19 mg/g for Pb(II), and 312.50, 277.78, and 263.16 mg/g for Cd(II). ZIF-8 (N) showed the most rapid sorption of lead and cadmium (in 15 min) whereas ZIF-8 (H) and ZIF-8 (M) similarly achieved equilibrium in 240 min and 300 min for the adsorption of lead and cadmium, accordingly. Both lead and cadmium adsorption is a good match with the pseudo-second-order kinetic and Langmuir isotherm. All ZIF-8s synthesized using different solvents demonstrated good capabilities in adsorbing lead and cadmium ions, although ammonia and aqueous solution as the solvent provided better removal than methanol.