Microflowers of Pd doped ZnS for visible light photocatalytic and photoelectrochemical applications

A new modification of zinc sulfide, which is microflowers of Pd doped ZnS, is investigated as photocatalyst for hydrogen generation from water. Pd doped ZnS shows significant photocatalytic activity when irradiated with visible light compared to ZnS. Both ZnS and Pd doped ZnS exist as cubic phase and in Pd doped ZnS, Pd substitutes Zn in the ZnS lattice. A change in the morphology of ZnS from irregular shape to rose flower like structure and increased surface area are observed after Pd doping. Increased visible light absorption and a red shift in the absorption edge is observed for the doped ZnS. Photoluminescence spectra suggest the presence of defect energy levels/surface states within the bandgap of ZnS due to the zinc and sulfide ion vacancies. Palladium exists as Pd2+ in doped ZnS and formation of metallic Pd does not occur after photocatalysis experiment. Photocatalytic activity of Pd doped ZnS shows the trend: 5%Pd-ZnS > 3%Pd-ZnS > 2%-Pd-ZnS > 6% Pd-ZnS > ZnS. The catalyst is stable for repeated use up to 60 h. Photoelectrochemical studies show enhanced photocurrent for the doped ZnS, which is in conformity with its photocatalytic property. These improved properties of the Pd doped ZnS is ascribed to the increased visible light absorption and to the increased surface area.