SIMPLE ONE-POT HYDROTHERMAL SYNTHESIS AND PHOTOCATALYTIC ACTIVITY OF ZnS AND ZnS/KAOLINITE NANOCOMPOSITE

This study is focused on preparation of pristine zinc sulphide (ZnS) and zinc sulphide/kaolinite (ZnS/K) nanocomposite using one-pot hydrothermal synthesis under atmospheric pressure and without any surfactant. Together with finding a simple preparation method, the aim was to achieve a high photocatalytic activity, and also reduce the environmental risk of ZnS (in the case of ZnS/K). Pristine ZnS was synthesized from aqueous solutions of zinc chloride and sodium sulphide in various ratios. ZnS/K nanocomposite was prepared similarly by addition of kaolin KKAF into the mixture of zinc chloride and sodium sulfide solutions. Reaction mixtures were continuously stirred at 100 degrees C for several hours, resulting white solids were separated by centrifugation, washed with distilled water, and dried at 105 degrees C overnight. X-ray powder diffraction analysis revealed the presence of cubic modification sphalerite both in ZnS and ZnS/ K samples. Amount of ZnS in ZnS/ K (similar to 32 wt.%) was determined by Rietveld method which also confirmed the sphalerite structure. Morphology of the samples was observed using scanning electron microscopy. In the case of ZnS/K, the ZnS nanoparticles anchored on the kaolinite surface were observed. Photocatalytic activity evaluated using discoloration of Acid Orange 7 (AO7) in a liquid phase was found very high for ZnS samples. After 1 h of UV irradiation, similar to 99 % of AO7 was degraded by ZnS. Photodegradation efficiency reached 96 % in the case of ZnS/K. Taking into account that only similar to 32 wt.% of ZnS is present in ZnS/K, the photocatalytic activity of the nanocomposite can be considered three times higher compared to pristine ZnS.