## 3 Results and Discussion
### Photocatalytic Activity of TiO\({}_{2}\)/ZnO  
The photocatalytic efficiency of the two types of as-prepared powders (annealed at 500 and 700 \({}^{\circ}\)C) was assessed through the use of UV-light illumination. There was no discernible decolorization of the dye solution in the control experiment, which involved exposing an aqueous solution of Tartrazine to UV light without the use of catalysts. According to the results, photolysis can cause up to 10% of the dye to be lost in 75 min. Spectrophotometric measurements were made of the Tartrazine decolorization rate over time at a wavelength of 430 nm, which is the wavelength of maximum absorbance. Figure 4 demonstrates the Tartrazine photodegradation by ultraviolet light irradiation using sol-gel powders annealed at 500 \({}^{\circ}\)C. The experiments, carried out with TiO\({}_{2}\)/ZnO powders, show a much higher decolorization rate of dye in comparison with pure TiO\({}_{2}\). As seen from Figure 5a, 10 TiO\({}_{2}\)/90 ZnO has the highest photocatalytic efficiency. The other sample, 90 TiO\({}_{2}\)/10 ZnO, has a higher photocatalytic efficiency than pristine TiO\({}_{2}\) (Figure 5a). The explanation of these results is not entirely clear, and is likely to be a complex combination of various factors. According to the SEM images (Figure 2), one can conclude that the enhancement in photocatalytic activity with increasing zinc oxide content can be attributed to the homogeneous and rough surface structure with very small particles. Figure 4: UV–visible spectra of the investigated gels. The rate constant (k) of the prepared samples confirms the percentage of degradation of the pollutant and is calculated by the formula \(-\)Ln(C/C\({}_{0}\)) = kt, where C\({}_{0}\) and C represent the initial and current pollutant contents, respectively. The rate constants for pure TiO\({}_{2}\), 90 TiO\({}_{2}\)/10 ZnO, and 10 TiO\({}_{2}\)/90 ZnO powders were 0.0096 min\({}^{-1}\), 0.0217 min\({}^{-1}\), and 0.0284 min\({}^{-1}\). Consequently, the TiO\({}_{2}\)/ZnO sol-gel photocatalysts demonstrated outstanding activity in the Tartrazine photodecomposition process. This trend, where a mixed photocatalyst performs better than a pure one, has also been shown by previous literature data [34; 35]. Figure 6 illustrates a possible mechanism for the decomposition of Tartrazine by TiO\({}_{2}\)/ZnO powders based on the results shown. The enhanced efficiency of the charge carrier separation resulting from the charge transfer between ZnO and TiO\({}_{2}\) may be the cause of the improved activity in photodegradation. Charge carriers are produced concurrently by UV illumination excitation and accumulate on the valance (VB) and conduction (CB) bands of TiO\({}_{2}\) and ZnO, respectively. Reduced photocatalytic efficiency could arise from the photo-induced electrons and holes produced by TiO\({}_{2}\) rapidly recombining with one another without being modified by ZnO. After ZnO is added, some sub-bands are created in the forbidden band by adding impurity defect levels, which cause the energy gap to shrink. Furthermore, the TiO\({}_{2}\)/ZnO powder's capacity to capture UV light is enhanced by TiO\({}_{2}\)'s narrowing band gap [36; 37; 38]. Additionally, the charge carrier recombination rate is suppressed as a result of the synergistic effects between ZnO and TiO\({}_{2}\). The availability of additional electrons and holes allow for the break-down of impurities and improved photocatalytic efficiency. Additionally, photo-induced electrons are mostly consumed in two ways: first, they react with H\({}_{2}\)O and O\({}_{2}\) that have been adsorbed on the catalysts' surface, producing some radicals and negative ions [39; 40]. To expedite the separation process, the second method involves combining dissolved O\({}_{2}\) in water, which consumes electrons [41; 42]. As previously mentioned, the holes from TiO\({}_{2}\) and electrons from ZnO may move to the corresponding bands of the opposite material, aiding in the separation of charge carriers.