The Effect of Heat Treatment on the Sol-Gel Preparation of TiO2/ZnO Catalysts and Their Testing in the Photodegradation of Tartrazine

This study aims to synthesize TiO2/ZnO powders and to study the effect of heat treatment on their photocatalytic ability against the Tartrazine anionic dye. The as-obtained powders with the following compositions-90TiO2/10ZnO and 10TiO2/90ZnO (mol%)-were obtained by the sol-gel technique. The prepared gels were annealed at 500 degrees C and 700 degrees C and subsequently characterized by XRD, UV-Vis, and SEM methods. The single crystalline phase of TiO2, which has been detected at up to 500 degrees C is anatase, while for ZnO, it is the hexagonal wurtzite structure. Further increases in the temperature (700 degrees C) led to the appearance of rutile in the samples. The SEM analysis demonstrated that the binary oxide materials had irregular shaped particles with a tendency to agglomerate. The UV-Vis spectra of the gels exhibited a red shift in the cut-off of the 90TiO2/10ZnO sample compared with pure Ti(IV) butoxide. Photocatalytic tests showed that the investigated samples possessed photocatalytic activity toward Tartrazine. Compared with TiO2, the prepared TiO2/ZnO photocatalysts showed superior properties in the photodegradation of a Tartrazine water solution. The target photocatalysts' enhanced photocatalytic activities can be explained by their reduced band gap energy, improved surface physicochemical characteristics, separation of photo-induced electron-hole pairs, and lowered recombination rate. Higher photocatalytic activity was observed for powders annealed at 500 degrees C, with the 10TiO2/90ZnO (mol%) sample exhibiting the highest photocatalytic degradation of the used organic dye.