Tuning the Defects of Nanostructured Zinc Oxide for Enhanced Photocatalytic Degradation of Organic Pollutants

Defect engineering of semiconductors is a promising approach for enhancing their photocatalytic activity for organic pollutant degradation in water. In this study, we present an effective strategy to tune the type, location, and number of defects in nanostructured zinc oxide (ZnO) by controlling the atmosphere in which the material was prepared (from high to virtually no exposure to O₂). By decreasing O₂ exposure during the synthesis, ZnO displayed an increasing number of surface and near-surface O vacancies (as determined by x-ray photoelectron spectroscopy and photoluminescence) and fewer bulk defects (as indicated by electron paramagnetic resonance spectroscopy). This approach allowed establishing the role that these defects exert on the photocatalytic activity of ZnO in removing pollutants from water. The optimum photocatalytic activity was achieved with ZnO nanoparticles that are rich in surface O vacancies but poor in bulk Zn and O vacancies. This ZnO photocatalyst outperformed P25-TiO₂ in the degradation of phenol, both under ultraviolet (UV) (73% vs. 56% removal) and visible irradiation (15% vs. 6% removal). Furthermore, it maintained its activity upon reuse and proved versatile in the degradation of several types of pollutants (bisphenol A, rhodamine B, imidacloprid, and ibuprofen sodium), highlighting its potential for practical water treatment applications.