The effect of cobalt content in Zn/Co-ZIF-8 on iodine capping properties

Abstract We have tested for iodine sorption properties a variety of samples with ZIF-8 structure and various Zn/Co ratios (100/0, 95/5, 75/25, 50/50 and 0/100 in mol%). For iodine saturation, an excess of sublimated iodine crystals was used. We have observed that the prevailing trend for all compositions is adsorption of most of the iodine molecules by the internal surface and retaining them up to framework collapse. However, Co-doping results in a small decrease in the thermal stability of the samples after iodine saturation. Moreover, in the samples with high cobalt content, the part of iodine adsorbed by the external surface is higher than in zinc analogs. Combination of TGA and FTIR data evaluated the impact of lower flexibility of Co-linker bonds on the transfer of iodine molecules from the external surface of the crystals to internal pores.