Synergistic effect of exposed facets and surface defects of ZnO nanomaterials for photocatalytic ozonation of organic pollutants

Abstract

The development of efficient catalysts is of great significance in the photocatalytic ozonation process for organic wastewater treatment. However, the effect of exposed facets and surface defects of the catalyst on the photocatalytic ozonation performance is less covered. Herein, ZnO nanocomposites with different preferentially exposed crystal facets (ZnO-rod and ZnO-disk) were synthesized and used for photocatalytic ozonation of phenol. The characterization and density functional theory calculation results demonstrated that the exposed {0001} facets and oxygen vacancies promoted the separation and transfer of photogenerated charges as well as improved the adsorption and activation of ozone molecules on the catalyst surface. Consequently, the TOC removal rate in the UV-O₃/ZnO-disk process (62.4%) was much higher than those in the UV-O₃/ZnO-rod process (41.3%) and the UV-O₃ process (15%). Moreover, the experimental results of the identification and quenching of active species illustrated that ˙OH was more likely to be produced in the UV-O₃/ZnO-disk process, while ¹O₂ was more likely to be formed over ZnO-rod. A large amount of ˙OH with a stronger oxidation capability than ¹O₂ contributed to the superiority of ZnO-disk over ZnO-rod in organic pollutant removal. This work demonstrates that the engineering of crystal facets and surface defects provides an effective strategy for constructing efficient catalysts for the photocatalytic ozonation process.