Fabrication of ZnO, ZnS, Ag-ZnS, and Au-ZnS microspheres for photocatalytic activities, CO oxidation and 2-hydroxyterephthalic acid synthesis

This paper reports the synthesis of ZnS microspheres with cubic and hexagonal crystal phases using a solvothermal method. These materials were characterized by a range of techniques. The effects of Au and Ag-doping on ZnS were also examined. Hexagonal phase ZnO microspheres could be obtained by a CO oxidation process over the ZnS microspheres. The onset of CO oxidation occurred above 350 degrees C, which was increased by Au and Ag doping. The synthesized materials were used for the photocatalytic degradation of mixed dyes {methylene blue (MB) + methyl orange (MO) + rhodamine B (RhB)}. The observed photocatalytic degradation rate over the photocatalysts was in the order, RhB < MB << MO. The photocatalytic degradation activity of the synthesized materials was observed in the order, Au-ZnS approximate to Ag-ZnS << ZnS < ZnO. ZnO was similar to 6 times more efficient in the photocatalytic synthesis of 2-hydroxyterephthalic acid than the ZnS and metal-doped ZnS. These results further support the importance and wide applications of the synthesized ZnS, Ag-ZnS, Au-ZnS and ZnO microspheres. (C) 2016 Elsevier B.V. All rights reserved.