The ZIF-8 crystals were synthesized with modifications to the previously reported method . The synthesis started with the preparation of two solutions, one by dissolving 0.505 g of zinc chloride (ZnCl2, Sigma-Aldrich, 98.0%)) in 25 mL of methanol, and another containing 0.608g of 2-methylimidazole (2-MeIm) and 0.505 g of NaHCO2 (Sigma-Aldrich, 99.0%) in the same amount of methanol. The solutions were mixed separately and then the 2-MeIm solution was poured into the ZnCl2 solution under stirring. The solution with a molar ratio of 1 Zn: 2 2-MeIm: 2 NaHCO2: 333 MeOH was transferred to a Teflon-lined stainless-steel autoclave in a preheated convection oven at 130°C for 4 h under homogeneous heating. The resultant crystals were then separated from the colloidal solution by three cycles of centrifugation (6000 rpm, 15 min) and washed with methanol under ultrasound. The morphology and crystallographic properties of ZIF-8 crystals were examined using scanning electron microscopy (SEM, Amray 1910) and X-ray powder diffraction (XRD, Malvern PANalytical Aeris) with a scan step of 0.015°.