Photocatalytic degradation of acid orange 7 over p-n type photocatalysts under illumination and absence of light

Abstract

Nowadays, a large amount of dyewastes, mainly synthetic dyes is continuously released by the textile industry. The component of this dyes, especially acid orange 7 (A07), can block a sunlight penetration and oxygen dissolution in water, leading to seriously environmental and health problems. For removal of dyewastes, photocatalysis is one of the most valuable techniques. Although it is a great application in dyewaste treatment, the photocatalytic reaction could not take place without illumination. For that reason, it is of interest to further improve the photocatalytic activity without illumination. To achieve that, the p-n junction semiconductor is used as a model to store the oxidation energy when there is no illumination. A p-n catalyst was formed by doping n-type TiO2 with p-type ZnO and p-type v2O5 as an oxidation energy storage catalyst. The sol-gel method was used to form a bilayer film catalyst (ZnO/TiO2 and V2O5/TiO2) coated on a glass slide substrate. The calcination temperature effect of ZnO and V2O5 on the photocatalytic activity was investigated, and the ZnO and V2O5 loading was also studied. The result showed that the highest degradation with 300ZnO/TiO2 film, at 300 °C calcination temperature of ZnO particles, was about 32.5% with illumination and 2.4% with no illumination. Furthermore, the photocatalytic activity was increased with increasing in the ZnO loading and reached the maximum at 98 wt%. In contrast, the photocatalytic activity of the V2O5/TiO2 film hardly affected the AO7 degradation.