# Photocatalytic Phenol Degradation by Silica-Modified Titanium Dioxide
## 3 Results
### Characterization of Particle Size Distribution of TiO\({}_{2}\)/SiO\({}_{2}\) Composites  
The particle size distribution of TiO\({}_{2}\) P25 and TiO\({}_{2}\)/SiO\({}_{2}\) composites were analyzed using a particle size analyzer (PSA). The data presented in Figure 4 show that the particles were homogeneous, which is indicated by only one peak on the histogram of each sample. Data regarding the mode values, mean, median, z-average, and polydispersity index (PI) are shown in Table 6. \begin{table}
\begin{tabular}{c c} \hline \hline
**Catalyst** & **BET Surface Area (m\({}^{2}\)/g)** \\ \hline TiO\({}_{2}\) P25 & 44.093 \\ SiO\({}_{2}\) & 185.191 \\ TiO\({}_{2}\)/SiO\({}_{2}\) (1:1) & 63.890 \\ TiO\({}_{2}\)/SiO\({}_{2}\) (3:1) & 53.934 \\ TiO\({}_{2}\)/SiO\({}_{2}\) (7:1) & 46.019 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The specific surface area of the photocatalyst. Figure 3: Surface morphology of (**a**) TiO\({}_{2}\) P25 [32], (**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. From the data in Table 6, it was observed that the addition of SiO\({}_{2}\) to a composite in the right composition caused the z-average or the average size of the particles to become smaller. In addition, the most occurring particle size was observed from the mode value. The mode value of each composite variations 1:1, 3:1, and 7:1 is 232.6, 204.5, and 204.8 nm, respectively. Meanwhile, the mode value of TiO\({}_{2}\) P25 was 236.6 nm and the mean particle size value for the TiO\({}_{2}\) and TiO\({}_{2}\)/SiO\({}_{2}\) composite variations 1:1, 3:1, and 7:1 is 288.2, 322.8, 320.2, and 223.4 nm, respectively. The polydispersity index (PI) value is a measurement of the molecular mass distribution in the sample. It is expressed as the weight average molecular weight divided by the number average molecular weight. Results from the study carried out by [PERSON] et al. [37] (in [PERSON] et al. [38]) states that if the PI value is less than 0.3, it indicates that the sample has a narrower distribution of nanoparticles and the size of the nanoparticle diameter is uniform or homogeneous. However, it was very difficult to make particles of a uniform size (monodispersion), and although monodispersion of particle size was obtained, it was actually a polydispersion particle with a very narrow particle size distribution. From Table 6, it was observed that the PI value for the TiO\({}_{2}\)/SiO\({}_{2}\) composites variations 1:1, 3:1, and 7:1 is 0.434, 0.387, and 0.353, respectively. Furthermore, the PI values of these samples fell into the mean range of the polydispersity index 0.3-0.7, where the distribution operated best. From the average particle size data and PI in Table 6, it was observed that the \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Measurement**} & \multicolumn{4}{c}{**Particle Size (nm)**} \\ \cline{2-5}  & **TiO\({}_{2}\) P25** & **TiO\({}_{2}\)/SiO\({}_{2}\) (1:1)** & **TiO\({}_{2}\)/SiO\({}_{2}\) (3:1)** & **TiO\({}_{2}\)/SiO\({}_{2}\) (7:1)** \\ \hline Mode & 236.6 & 232.6 & 204.5 & 204.8 \\ Mean & 251.7 & 248.1 & 220.1 & 210.9 \\ Median & 247.4 & 240.7 & 208.7 & 206.6 \\ Z-Average & 288.2 & 322.8 & 320.2 & 223.4 \\ PI & 0.399 & 0.434 & 0.387 & 0.353 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Data measurement results using a PSA (particle size analyzer). Figure 4: PSA histogram (**a**) TiO\({}_{2}\) P25, (**b**) TiO\({}_{2}\)/SiO\({}_{2}\) 1:1 ratio, (**c**) TiO\({}_{2}\)/SiO\({}_{2}\) 3:1 ratio, and (**d**) TiO\({}_{2}\)/SiO\({}_{2}\) 7:1 ratio. TiO\({}_{2}\)/SiO\({}_{2}\) 7:1 variation had the smallest average particle size and the highest homogeneity. It can be understood that the amount of SiO\({}_{2}\) affects the sample size, in that a small amount of SiO\({}_{2}\) added can cause a decrease in the particle size. However, a large amount of SiO\({}_{2}\) will cause an increase in the agglomeration and therefore increase the particle size.