Correlation between Photocatalytic Properties of ZnO and Generation of Hydrogen Peroxide—Impact of Composite ZnO/TiO2 Rutile and Anatase

Abstract

The generation of hydrogen peroxide on commercial and synthesized ZnO from different precursors was studied using two model molecules, formic acid (FA) and phenol (Ph), as well as phenolic intermediates, hydroquinone (HQ), benzoquinone (BQ), and catechol (CAT). The samples were characterized using X-ray Diffraction (XRD), Transmission Electronic Microscopy (TEM), RAMAN, and Electron Paramagnetic Resonance (EPR) before evaluating their photocatalytic properties. We found that the improved efficiency is accompanied by a high level of H2O2 production, fewer oxygen vacancies, and that the number of moles of H2O2 formed per number of carbon atoms removed is similar to the degradation of FA and Ph with a factor of 1. Moreover, a comparative study on the formation of H2O2 was carried out in the presence of TiO2 rutile and TiO2 anatase, with commercial ZnO. Our results exhibit the impact of the presence of TiO2 on the decomposition of hydrogen peroxide and the formation of phenolic intermediates, which are much lower than those of ZnO only, which is in agreement with the formation of hydroxyl radicals °OH and superoxide O2°− degrading significantly hydroquinone (HQ), benzoquinone (BQ), and cathecol (CAT).