# Photocatalytic Phenol Degradation by Silica-Modified Titanium Dioxide
## 3 Results
### Characterization of Catalyst TiO\({}_{2}\)/SiO\({}_{2}\) Composite Structure
High crystallinity promoted a charge transfer from the center to the surface of the photocatalyst, which increased the photocatalytic activity [32]. The crystallite size is calculated based on the Scherrer equation. The calculated crystallite size is the average of each phase peak in the XRD pattern and is calculated with the standard deviation. Table 2 shows that the presence of SiO\({}_{2}\) can reduce the crystallite size. The largest crystallite size was found in the TiO\({}_{2}\)/SiO\({}_{2}\) 7:1 composite with anatase 16.28 \(\pm\) 2.30 and rutile 26.06 \(\pm\) 2.52. The size of this crystallite decreases with the amount of SiO\({}_{2}\). It can be understood that the more SiO\({}_{2}\) is added, the more defects and the amorphous phase will increase [29; 31; 33]. As a result, the crystallinity is getting smaller, which causes the peak of the XRD pattern to widen. With the widening of the XRD peak, the full width at half maximum (FWHM) value will be larger and the calculated crystal size will be smaller. The sample unit cell parameters and Rietveld refinement parameters are reported in Table 3. The Rietveld refinement plot is depicted in Figures S1-S4. From the table, it is known that the presence of SiO\({}_{2}\) caused a slight change in the anatase and rutile unit cells. From this value, it can be seen that SiO\({}_{2}\) will enlarge the unit cell of anatase and rutile. This trend is clearly seen by the presence of the largest unit cell, namely, in the TiO\({}_{2}\)/SiO\({}_{2}\) 1:1 composite with an anatase volume of 136.4306 A\({}^{3}\) and rutile volume of 62.4995 A\({}^{3}\). This volume decreases as the amount of SiO\({}_{2}\) decreases, and the smallest is found in TiO\({}_{2}\) P25 without SiO\({}_{2}\) added. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**Crystallinity (\%)**} & \multicolumn{2}{c}{**Crystallite Size 1 (nm)**} \\ \cline{2-3}  & & **Anatase** & **Rutile** \\ \hline TiO\({}_{2}\) P25 & 88.17 & 15.30 \(\pm\) 2.38 & 20.24 \(\pm\) 5.68 \\ TiO\({}_{2}\)/SiO\({}_{2}\) (1:1) & 87.49 & 16.04 \(\pm\) 2.42 & 21.99 \(\pm\) 6.35 \\ TiO\({}_{2}\)/SiO\({}_{2}\) (3:1) & 91.54 & 16.14 \(\pm\) 2.14 & 25.65 \(\pm\) 7.17 \\ TiO\({}_{2}\)/SiO\({}_{2}\) (7:1) & 92.52 & 16.28 \(\pm\) 2.30 & 26.06 \(\pm\) 2.52 \\ \hline \hline \end{tabular}  
* Data are shown as the mean \(\pm\) the standard deviation.  
\end{table} 
Table 2: The crystallinity and crystallite size of the samples. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Scheme**} & \multicolumn{5}{c}{**Unit Cell Parameters**} & \multicolumn{5}{c}{**Rietveld Refinement Parameters**} \\ \cline{2-9}  & \multicolumn{2}{c}{**Anatase**} & \multicolumn{5}{c}{**Rutile**} & \multirow{2}{*}{**Variables**} & \multirow{2}{*}{**Rexp**} & \multirow{2}{*}{**Rwp**} & \multirow{2}{*}{**GoF**} \\ \hline  & _a = b (Å)_ & _c (Å)_ & _Volume (Å\({}^{3}\))_ & _a = b (Å)_ & _c (Å)_ & & **Volume (Å\({}^{3}\))** & \\ \hline TiO\({}_{2}\) P25 & 3.7843 & 9.5040 & 136.1043 & 4.5920 & 2.9570 & 62.3545 & 12 & 2.65 & 4.22 & 2.53 \\ TiO\({}_{2}\)/SiO\({}_{2}\) (1:1) & 3. The next characterization was Fourier-transform infrared spectroscopy (FTIR), used to identify the functional groups in the TiO\({}_{2}\)/SiO\({}_{2}\) composites at wave number 450-4000 cm\({}^{-1}\). The resulting spectrum in Figure 2 shows that the characteristics of the IR absorption band at wave number 3410-3435 cm\({}^{-1}\) was a stretching vibration of -OH, while at 1633-1636 cm\({}^{-1}\), it was a typical absorption for the bending vibration of -OH [25]. The strong and dominant absorption peak discovered at wave number 1101-1103 cm\({}^{-1}\) was the asymmetric stretching vibration of the Si-O-Si (siloxane) bond [25]. Furthermore, the absorption peak appearing at the wave number 475.0 cm\({}^{-1}\) was caused by the vibration of the O-Si-O (siloxy) bond stretching. Meanwhile, the peaks discovered at 667-686 cm\({}^{-1}\) showed the vibration of the Ti-O-Ti bond stretching [34].