## 3 Results and Discussion
### Photocatalytic Activity of TiO\({}_{2}\)/ZnO
When ZnO was added to TiO\({}_{2}\), this significantly improved the separation efficiency. As a result, the photocatalytic properties increased. As the electrons jump from ZnO to TiO\({}_{2}\) (CB), the holes conversely move from ZnO (VB) to TiO\({}_{2}\). Additionally, the previously mentioned electrons and holes can take part in chemical reactions that lead to a decrease in the catalyst's recombination rate and separation of the photo-induced electron-hole pairs. Consequently, TiO\({}_{2}\)/ZnO photocatalysts exhibit better photocatalytic degradation of Tartrazine. Figure 5: Photocatalytic decomposition percent (**a**) and rate constants (**b**) of Tartrazine using pure TiO\({}_{2}\) and TiO\({}_{2}\)/ZnO powders annealed at 500 \({}^{\circ}\)C.  
The results from photocatalysis with the powders annealed at both temperatures were compared with respect to the percent degradation of Tartrazine and the rate constant k. The amount of dye also decreased at the higher temperature, but much more slowly in comparison with the respective powder at 500 \({}^{\circ}\)C (Figure 7). According to the X-ray data, as the temperature increases from 500 to 700 \({}^{\circ}\)C, titanium dioxide changes from anatase to rutile (Figure 1). This is the reason for the lower activity and slower degradation of the contaminant in the samples annealed at the higher temperature. Although the overall photocatalytic efficiency is improved when rutile TiO\({}_{2}\) is present as an impurity within the anatase state, the anatase form has higher photocatalytic activity than the rutile form [19]. A phase transition of TiO\({}_{2}\) occurs between the rutile (Eg = 3.10 eV), anatase (Eg = 3.36 eV), and brookite (Eg = 3.51 eV) states when the calcination temperature is enhanced [43]. It is recognized that the band gap energy tends to decrease when the transition from anatase to rutile occurs. The rutile form has the smallest band gap, making it difficult for electron transfer from zinc oxide to occur. Accordingly, fewer radicals are created, and the organic pollutant is broken down more slowly. The same trend is observed when the sample with the highest reaction rate and percent degradation of the pollutant is the one that has the highest zinc oxide content (10 TiO\({}_{2}\)/90 ZnO). This means that the incorporation of ZnO into TiO\({}_{2}\) increases the photo  
Figure 6: A probable mechanism for the enhanced property of TiO\({}_{2}\)/ZnO catalysts to e Tartrazine. Mechanism adapted with permission from Ref. [36]. Figure 7: Photocatalytic decomposition percent (**a**) and rate constants (**b**) of Tartrazine using pure TiO\({}_{2}\) and TiO\({}_{2}\)/ZnO powders annealed at 700 \({}^{\circ}\)C.  
The faster Tartrazine degradation at a lower catalyst preparation temperature is made possible by the larger surface area. Because of their better morphology and grain growth, the samples annealed at 500 \({}^{\circ}\)C showed higher photocatalytic efficiency than those heated at 700 \({}^{\circ}\)C. Elevating the surface area usually results in increased adsorption of substrates, thereby amplifying the electron-hole interactions with the substrates. A higher surface area, however, can also quicken the e\({}^{-}\)/h\({}^{+}\) recombination, which lowers the rate. The larger-surface-area photocatalyst is preferred when surface reaction dominates recombination and vice versa. This means that specific surface area affects the photoactivity. Figure 8 presents the findings of a three-cycle study on the recyclability of powders consisting of pure TiO\({}_{2}\), 9 TiO\({}_{2}\)/10 ZnO, and 10 TiO\({}_{2}\)/90 ZnO. For every type of catalyst, the photocatalytic decomposition of Tartrazine decreased by roughly 3% after three cycles in distilled water, indicating a slight decline in the powders' catalytic properties with each cycle. The dye decomposition cycle stability of the sol-gel powders was found to be good, even with this decrease.