# Photocatalytic Phenol Degradation by Silica-Modified Titanium Dioxide
## 3 Results
### Photocatalytic Activity Test of TiO\({}_{2}\)/SiO\({}_{2}\) Composites on Phenol  
Various previous studies have reported composites between TiO\({}_{2}\) and SiO\({}_{2}\). Several sources of SiO\({}_{2}\) are reported from various sources, such as extraction from natural materials and commercial SiO\({}_{2}\). Examples of studies using TiO\({}_{2}\) and SiO\({}_{2}\) composites from various sources are presented in Table 8. The SiO\({}_{2}\) used in this study was extracted from Bengkulu beach sand, Indonesia (extracted by [PERSON] et al. [24]). Research on TiO\({}_{2}\)/SiO\({}_{2}\) composites with SiO\({}_{2}\) as a source of sand is still rarely reported. The activity of the TiO\({}_{2}\)/SiO\({}_{2}\) composite photocatalysts was tested against the decrease in phenol concentrations to determine the performance of the synthesized photocatalysts compared to TiO\({}_{2}\) P25 Degussa. Phenol was chosen as a media for photocatalyst application because it is a toxic organic compound found in industrial waste in rivers and streams [4; 45]. This test was performed using a simulated sample of phenol standard solution that was analyzed using high-performance liquid chromatography. The results of the phenol photocatalytic test are shown in Figure 7.  
Figure 6: The proposed bandgap of the TiO\({}_{2}\)/SiO\({}_{2}\) composite and the potential levels of CB (conduction band) and VB (valence band) (vs. NHE). \begin{table}
\begin{tabular}{c c c c} \hline
**Composite** & **SiO\({}_{2}\) Source** & **Synthesis Method** & **Application** & **Ref.** \\ \hline TiO\({}_{2}\)/SiO\({}_{2}\) & Tetraethylorthosilicate (TEOS) & Sol-gel & Photocatalyst degrade of & [33] \\ TiO\({}_{2}\)/SiO\({}_{2}\) & Hexagonal silica & & 2-methylisobornel and geosmin & [43] \\ TiO\({}_{2}\)/SiO\({}_{2}\) & structures & Sonochemistry & Photocatalyst for removal formaldehyde & [43] \\ TiO\({}_{2}\)/SiO\({}_{2}\) & SiO\({}_{2}\) sol & Precipitation & Photocatalytic oxidation of benzene & [35] \\ TiO\({}_{2}\)/SiO\({}_{2}\) & Rice husk silica & Self-assembly & Photocatalytic decolorization of & [30] \\ TiO\({}_{2}\)/SiO\({}_{2}\) & Commercial SiO\({}_{2}\) (cabot, & & Photocatalytic degradation of 2-propanol, & [36] \\ TiO\({}_{2}\)/SiO\({}_{2}\) & SiO\({}_{2}\) powder & Sol-gel & Photocatalytic degradation of acid orange & [44] \\ \hline \end{tabular}
\end{table} 
Table 8: Comparison of various TiO\({}_{2}\)/SiO\({}_{2}\) composites with SiO\({}_{2}\) sources and their applications. From Figure 7, it was observed that the decrease in concentration until the 60 th min was the effect of adsorption from the photocatalyst since the test was carried out without UV light irradiation until the 60 th min. Furthermore, tests with UV light irradiation were carried out at 60 to 180 min, where a significant decrease in concentration was observed after activation of the photocatalyst by light. The TiO\({}_{2}\) photocatalyst added with SiO\({}_{2}\) resulted in a decrease in the phenol concentration, which was observed on a more descending curve. In the adsorption process until the 60 min, it was observed in the curve that TiO\({}_{2}\) had adsorption ability; however, the resulting decrease in concentration was lower. Meanwhile, when added with SiO\({}_{2}\), the adsorption ability increased significantly. The addition of SiO\({}_{2}\) to the TiO\({}_{2}\) photocatalyst was directly proportional to the percentage of phenol adsorption. The percentage of phenol reduction during the adsorption process (without UV light irradiation) using TiO\({}_{2}\) P25, for TiO\({}_{2}\)/SiO\({}_{2}\) composites with the variations 7:1, 3:1, and 1:1, is 4.60, 16.11, 19.45, and 21.48%, respectively. Data of the phenol concentration and percentage reduction at any time are presented in Table 9.  
The photocatalysts exhibited a higher percentage reduction under exposure to UV light. This indicated the performance in phenol oxidation is influenced by photons from UV light.