# Photocatalytic Phenol Degradation by Silica-Modified Titanium Dioxide
## 3 Results  
### Characterization of Catalyst TiO\({}_{2}\)/SiO\({}_{2}\) Composite Structure  
The structure and phase of the TiO\({}_{2}\) and TiO\({}_{2}\)/SiO\({}_{2}\) composites was observed from the diffraction patterns shown in Figure 1. These patterns showed the diffraction patternsof TiO\({}_{2}\) P25 Degussa and composites of TiO\({}_{2}\)/SiO\({}_{2}\). The standard atomic parameters of anatase TiO\({}_{2}\) (tetragonal, space group \(I4_{1}/amd\)) were taken from the Inorganic Crystal Structure Database (ICSD) 98-004-4882 [27] and ICSD 98-008-2085 for rutile structures (tetragonal, space group \(P4_{2}/mmm\)) [28]. The crystal of the TiO\({}_{2}\) P25 Degussa showed the highest peak pattern at 20 = 25.25\({}^{\circ}\) and several other distinctive peaks, specifically at 20 = 37.80\({}^{\circ}\) and 47.89\({}^{\circ}\) and twin peaks at 53.90\({}^{\circ}\) and 55.91\({}^{\circ}\), which are regions of anatase type TiO\({}_{2}\) crystal characteristics. All TiO\({}_{2}\)/SiO\({}_{2}\) composite diffractograms showed very similar peaks, the difference being the intensity and widening at certain peaks. Figure 1 shows that the composite composition affected the peak intensity and the sharpness of the resulting peak and that a large amount of SiO\({}_{2}\) caused a decrease in peak intensity and a band widening leading to reduced crystallinity (Table 1). These results are confirmed from a previous study reported by [PERSON] and [PERSON] [29]. Another reason for the reduced peak intensity is that possibly the inter lattice between Ti, O, and Si was formed during the synthesis process [30]. This result can be seen with the appearance of a new peak at 20 = 31.68\({}^{\circ}\). The FTIR technique was used to confirm the presence of these Ti-O-Si bonds, which will be discussed later. Phase percentages showed in Table 1 were obtained using Rietveld refinement (Figures S1-S4) of the XRD patterns in the composite showing the percentages of anatase and rutile phase. From the data in Table 1, it is observed that TiO\({}_{2}\)/SiO\({}_{2}\) 1:1 has the highest anatase phase followed by TiO\({}_{2}\)/SiO\({}_{2}\) 3:1 and TiO\({}_{2}\)/SiO\({}_{2}\) 7:1. The composite of TiO\({}_{2}\)/SiO \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{**Phase Composition (\%)**} \\ \cline{2-3}
**Sample** & **Anatase** & **Rutile** \\ \hline TiO\({}_{2}\) P25 & 86.3 & 13.7 \\ TiO\({}_{2}\)/SiO\({}_{2}\) (1:1) & 88.2 & 11.8 \\ TiO\({}_{2}\)/SiO\({}_{2}\) (3:1) & 86.8 & 13.1 \\ TiO\({}_{2}\)/SiO\({}_{2}\) (7:1) & 85.9 & 14.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Percentage of phase composition of the samples. Figure 1: X-ray diffraction pattern of (**a**) TiO\({}_{2}\) P25, (**b**) TiO\({}_{2}\)/SiO\({}_{2}\) composite 1:1 ratio, (**c**) TiO\({}_{2}\)/SiO\({}_{2}\) composite 3:1 ratio, and (**d**) TiO\({}_{2}\)/SiO\({}_{2}\) composite 7:1 ratio. 1:1 has the smallest rutile percentage; this indicates that the presence of SiO\({}_{2}\) will inhibit the formation of the rutile phase from anatase [14; 31]. Furthermore, materials with an amorphous phase showed a wide band when analyzed using XRD due to the irregular arrangement; that is, this material was rigid and does not have a certain geometric shape. SiO\({}_{2}\) with its surface amorphous phase had more defects that interacted with the contaminants; meanwhile in the crystalline SiO\({}_{2}\), the structure was regular and the bond was more stable, which made it less capable of adsorption and easier desorption [25]. In addition, the amorphous SiO\({}_{2}\) structure affected the TiO\({}_{2}\) structure in the composite, which resulted in a decrease in intensity and a widening at the peak, indicating that the crystallinity of TiO\({}_{2}\) decreased. The TiO\({}_{2}\)/SiO\({}_{2}\) 1:1 composite showed the lowest crystallinity value due to the effect of the most addition of SiO\({}_{2}\), while TiO\({}_{2}\)/SiO\({}_{2}\) 7:1 had the higher crystallinity (Table 2).