Zinc Oxide and Structural Defects for Photocatalysis: Between Challenges and Reality

SSCI-VIDE+CARE+NHM:CGU:FDAInternational audienceZnO photocatalytic materials have been prepared using three zinc sources and a simple synthetic approach, either from direct precipitation of Zn(CH3COO)2 or via a thermal conversion from Zn(OH)2 or ZnO2. The calcination at various temperatures has been employed to generate materials with different reactivities and the effect of different parameters such as impurities, surface area and structural defects on the photocatalytic properties of ZnO have been investigated. X-Ray Diffraction (XRD), UV-Vis, BET, X-ray photoelectron spectroscopy (XPS), Raman, and Electron Paramagnetic Resonance (EPR) have been used to correlate the impact of the surface area, the introduction of oxygen and/or zinc vacancies, and the charge carrier dynamics, with their photocatalytic properties for the model degradation of formic acid and phenol under UV-irradiation. The main objective is to provide a new approach to the impact of structural defects on ZnO semiconductors determined by using Raman and EPR techniques and by coupling with the important role of the surface area considered as one of the most relevant characteristics in photocatalysis in terms of performance. We found that at similar surface area, the presence of oxygen vacancies and/or zinc vacancies decreases the disappearance rate of both model pollutants and favors the recombination rate of electron/hole contrary to the conclusions generally assumed in the literature. Moreover, our work indicates that the presence of organic impurities in the photocatalyst has not the same impact on formic acid and phenol due to their competition of degradation probably correlated to their adsorption. Overall, surface area and structural defects are complementary to each other, directly dependent on the choice of the precursor, and needs to be considered in a strategy towards efficient ZnO photocatalyst