Mechanochemical synthesis of nanoparticulate ZnO–ZnWO4 powders and their photocatalytic activity

In this study, mechanochemical reaction systems with H2WO4 as a precursor were investigated for the synthesis of nanoparticulate powders of WO3, ZnWO4, and dual-phase (ZnWO4)x(ZnO)1–x. The objective was to establish whether mechanochemical processing can be used to manufacture high activity photocatalysts in the ZnO–WO3 system. Milling and heat treatment of H2WO4 + 12NaCl was found to result in the formation of irregularly shaped platelets of a sodium tungstate rather than nanoparticles of WO3. Powders of single-phase ZnWO4 and dual-phase (ZnWO4)x(ZnO)1–x were successfully synthesised by incorporating H2WO4 into the ZnCl2 + Na2CO3 + 4NaCl reactant mixture. The photocatalytic activity of these powders was evaluated using the spin-trapping technique with electron paramagnetic resonance spectroscopy. It was found that the photocatalytic activity decreased with the ZnWO4 content. This decrease in activity was attributed to the larger average particle size of the ZnWO4 component compared to the ZnO, which reduced the surface area available for interfacial transfer of the photogenerated charge carriers.