The photocatalytic phenol degradation mechanism of the Ag-modified ZnO nanorods
Photocatalysis as a potential green technology can effectively degrade organic pollutants in the environment. The change rule of intermediate products in the photocatalytic degradation process of pollutants is particularly important. In this paper, the ZnO porous nanorods (NRs), ZnO/Ag and ZnO/Ag/Ag2O photocatalysts were prepared and their photocatalytic phenol degradation performance was investigated. Compared with ZnO NRs and ZnO/Ag, ZnO/Ag/Ag2O displays a significantly enhanced photocatalytic phenol degradation performance and can achieve complete degradation of phenol after only 90 min of white light illumination. The photocatalytic phenol degradation processes were emphatically analyzed in detail using different photocatalysts in the present work. Except for the direct ring-opening reaction of phenol, the hydroquinone is the main intermediate product for the photocatalytic phenol degradation by ZnO NRs and ZnO/Ag. However, for ZnO/Ag/Ag2O photocatalyst, the Ag/Ag2O NPs, which act as the acceptors of the photogenerated electrons and play important role for the phenol degradation, present on the surface of the ZnO NRs. The intermediate products of p-benzoquinone and hydroquinone are found during the phenol degradation process. Different from ZnO NRs and ZnO/Ag, ZnO/Ag/Ag2O can selectively catalyze the formation of p-benzoquinone due to the important role of Ag/Ag2O NPs. The p-benzoquinone intermediate was produced due to the generation of a large amount of •O2- through the mutual conversion of Ag0 and Ag+ on the Ag/Ag2O NPs. Therefore, ZnO/Ag/Ag2O accelerates the oxidation and degradation of phenol to carbon dioxide and water through different intermediate processes under white light illumination. Finally, the mechanism of photocatalytic phenol degradation by ZnO/Ag/Ag2O is proposed in this paper.