Formation of surface defects by thermal shock method for the improved photocatalytic activity of ZnO nanoparticles

Surface-modified ZnO photocatalysts with enhanced UVA-light-driven and visible-light-driven activities were synthesized by the thermal shock method with Cu(NO₃)₂ at different thermal shock temperatures (300–600°C). The influences of thermal shock temperatures on the crystal structure, morphology, surface functional groups and surface composition of modified catalysts were investigated by XRD, TEM, Raman and XPS spectra, respectively. Their photocatalytic activity was evaluated via the degradation of methylene blue under both UVA and visible light irradiation. According to the results, by combining the thermal shock method and an agent with low thermal stability such as Cu(NO₃)₂, we did not modify the crystal structure, phase composition nor the morphology of ZnO nanoparticles, but successfully modified the surface of ZnO nanoparticles with the migration of zinc ions, leading to the creation of new environments of Zn²⁺ and O^{2 –} ions as well as the formation of surface zinc vacancies. These evolutions were found to be able to enhance the photocatalytic performance in the UVA light region and also in the visible light region.