Abstract
ABSTRACTSurface-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 O2 – 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.
Highlights
Over the past decades, photocatalysis based on the performance of various transition metal oxides like ZnO has been considered as one of the most promising methods for water treatment [1,2,3,4]
The TEM images of all samples show the same morphology, with polyhedral particles in the size distribution from 20 to 100 nm (Figure 2). These results demonstrate that the thermal shock process with Cu(NO3)2 at different temperatures did not modify the phase composition, crystal structure and the particle size of ZnO nanoparticles
The experimental results demonstrated that the thermal shock method with or without Cu(NO3)2 barely lead to any modification in the crystal structure, phase composition and morphology of ZnO nanoparticles
Summary
Photocatalysis based on the performance of various transition metal oxides like ZnO has been considered as one of the most promising methods for water treatment [1,2,3,4]. Several works revealed that the creation of intrinsic or extrinsic defects such as oxygen vacancies, zinc vacancies, zinc interstitials and impurities can help to effectively control the photocatalytic performance of ZnO. According to the work of Chen et al [9], when the oxygen vacancies or zinc vacancies are formed in the bulk structure of ZnO, they can act as the recombination centers of photogenerated charges, preventing the transport of photogenerated electrons and holes to the surface and their reactions with adsorbed species. By using a simple ballmilling technique, Aggelopoulos et al successfully created the oxygen vacancies in ZnO lattice and observed the systematic decrease in photocatalytic activity when the milling time increased [10]
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