Methyl red dye-sensitized zinc oxide as photocatalyst for phenol degradation under visible light

摘要

Zinc oxide (ZnO) is one of the semiconductor photocatalysts having large band gap energy, which is usually enough for the degradation of organic pollutant such as phenol. However, large band gap energy also means that ZnO is mostly active under UV light only. In this study, ZnO was sensitized using a methyl red dye and the improved photocatalytic activity was confirmed for degradation of phenol under visible light irradiation. The ZnO was first prepared by a hydrothermal method, then was sensitized with methyl red (MR) dye through an impregnation method with various contents of MR (1-3 wt%). Fourier transform infrared spectra indicated a change in methyl red structure after impregnation on ZnO due to the basicity of ZnO. While the MR addition did not affect the band gap energy of ZnO, it improved the optical properties of ZnO in the visible light region. Fluorescence spectra revealed that the addition of 1 and 2 wt% MR slightly red-shifted the excitation maxima of ZnO, while 3 wt% addition resulted in a blue-shift. Furthermore, it was shown that ZnO has an oxygen vacancy with emission at 558 nm and the presence of methyl red quenched the emission intensity. The photocatalytic activity of ZnO increased after dye sensitizing, where the best performance was obtained on the ZnO with 2 wt% of MR addition. The better photocatalytic activity of ZnO after dye sensitization could be proposed due to the additional electron transfer from MR to ZnO generated under visible light irradiation.