## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Calcination Temperature** & **Comment** & **Reference** \\ \hline \multirow{3}{*}{25–800 \({}^{\circ}\)C} & \multicolumn{2}{c}{Calcination temperature below 600 \({}^{\circ}\)C found the mixture of} & \multirow{3}{*}{[26]} \\  & anatase and brookite phases. The rutile phase was found & \\  & above 600 \({}^{\circ}\)C and only the rutile phase was found at 800 \({}^{\circ}\)C. & \\ \hline \multirow{3}{*}{300–600 \({}^{\circ}\)C} & Pure anatase phase was found between 300 \({}^{\circ}\)C and 400 \({}^{\circ}\)C. & \\  & Rutile was found above 500 \({}^{\circ}\)C. & \\ \hline \multirow{3}{*}{200–800 \({}^{\circ}\)C} & Pure anatase was found between 200 \({}^{\circ}\)C and 400 \({}^{\circ}\)C. The & \\  & rutile phase was found above 500 \({}^{\circ}\)C. & \\ \hline \multirow{3}{*}{400–700 \({}^{\circ}\)C} & \multicolumn{2}{c}{Calcination temperature below 700 \({}^{\circ}\)C found only pure} & \multirow{3}{*}{[35]} \\  & anatase and calcination temperature of 700 \({}^{\circ}\)C found the & \\ \cline{1-1}  & mixture of anatase and rutile phases. & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Phase transition of TiO\({}_{2}\) synthesized via sol-gel method and calcined with different calcination temperatures. Figure 4: (**a**) Relationship between calcination temperature before and after calcination temperatures from 300 \({}^{\circ}\)C to 800 \({}^{\circ}\)C and percentage of phase content of synthesized TiO\({}_{2}\), (**b**) diffuse reflectance spectroscopy (DRS) spectra of TiO\({}_{2}\) with different calcination temperatures. The methylene blue adsorption capability of synthesized TiO\({}_{2}\) and P25 is shown in Figure 5a. Before UV light illumination, the solutions were kept in dark for 1 h under stirring to saturate the adsorption of MB. It was observed that the concentration of MB solutions of TiO\({}_{2}\)-600, TiO\({}_{2}\)-650, TiO\({}_{2}\)-700, TiO\({}_{2}\)-800, and P25 was reduced about 10% of initial MB solutions while TiO\({}_{2}\)-300, TiO\({}_{2}\)-400 and TiO\({}_{2}\)-500 showed negligible adsorption capability of MB under dark condition. Figure 5b presents the study of photocatalytic activity of synthesized TiO\({}_{2}\) nanoparticles with different calcination temperatures from 300 \({}^{\circ}\)C to 800 \({}^{\circ}\)C and a comparison with commercial P25 TiO\({}_{2}\) nanoparticles as a reference. Table 3 shows the kinetic constant of MB degradation of synthesized TiO\({}_{2}\). The effect of calcination temperature on phase transition of synthesized TiO\({}_{2}\) powders provided the different kinetic constants as shown in Figure 6a. It was observed that P25 with 89:11 of anatase to rutile showed the highest photocatalytic activity with the kinetic constant of \(11.41\times 10^{-2}\) h\({}^{-1}\). However, among synthesized TiO\({}_{2}\), TiO\({}_{2}\)-600 provided the highest photocatalytic activity with the kinetic constant of 9.46 \(\times\) 10\({}^{-2}\) h\({}^{-1}\). Increasing calcination temperature from 300 \({}^{\circ}\)C to 400 \({}^{\circ}\)C, the kinetic constant increased from \(2.54\times 10^{-2}\) to \(3.87\times 10^{-2}\) h\({}^{-1}\). Photocatalytic activity of TiO\({}_{2}\) depends on many factors such as phase composition, crystal structure, crystallinity, crystallite size, and surface area [38]. TiO\({}_{2}\)-300 and TiO\({}_{2}\)-400 composed of anatase and brookite phases and there was an increase of anatase phase from 29%wt. (TiO\({}_{2}\)-300) to 33%wt. (TiO\({}_{2}\)-400). Commercial P25 showed higher photocatalytic activity than synthesized TiO\({}_{2}\) because P25 presented a higher ratio of anatase to rutile (89:11) than that of TiO\({}_{2}\)-600 (42:30). While the particle sizes of P25 and TiO\({}_{2}\)-600 were quite similar as \(19.9\pm 1.2\) nm and \(18.7\pm 3.7\) nm, respectively. Our photocatalytic oxidation result is agreed well with the study of [PERSON] et al.