## 3 Results and Discussions
### Photocatalytic Activity
#### 3.5.1 Degradation of Bentazon Herbicide  
The photodegradation of bentazon in the presence of 20 mg TiO\({}_{2}\) catalyst, 5 ppm pollutant concentration, and at pH 6, 7, 8, and 9 was carried out for 40 min under UV light. The obtained degradation efficiency was 81%, 99%, 43%, and 23% at pH 6, 7, 8, and 9, respectively, as shown in Figure 5a. The maximum degradation efficiency was obtained at pH = 7; thus, all photocatalytic experiments were performed at pH 7 under UV and sunlight irradiation. Figure 5b,c shows the absorption spectra of BZ at different time intervals. The presence of a catalyst leads to a decrease in the absorption spectra at \(\lambda\) = 334 nm as a function of irradiation time, as shown in Figure 5a,b. The photocatalytic degradation efficiency of the TiO\({}_{2}\) catalyst against bentazon in 40 min was 99% and 75% under UV light and sunlight, respectively, as displayed in Figure 5d. Additionally, the kinetic study of photodegradation was examined using a first-order model as follows [29]:  
\[C_{t}=C_{o}e^{-kt} \tag{3}\]  
\[ln\ (\frac{C_{o}}{C_{t}})=kt \tag{4}\]  
where \(k\), \(C_{o}\), and \(C_{t}\) represent the rate constant, and concentration of BZ before and after degradation under illumination as a function of time, respectively. The obtained results against the photodegradation of bentazon reveal that percentage degradation efficiency and rate constant \(k\) are higher under UV light as compared to sunlight. A literature comparison of the photocatalytic activity of TiO\({}_{2}\) for the degradation of bentazon at different experimental conditions is given in Table 2. The values of rate constants (k) and \(R^{2}\) for BZ are listed in Table 3.  
Figure 4: UV-Visible absorption spectra of the TiO\({}_{2}\) photocatalyst in the range of 200–800 nm. The inset shows the Tauc plot for the energy bandgap. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Catalyst**} & \multicolumn{2}{c}{**Catalyst**} & \multirow{2}{*}{**Irradiation**} & \multicolumn{2}{c}{**Bentazon**} & \multirow{2}{*}{**V\% Degradation**} & \multirow{2}{*}{**Ref.**} \\  & **Concentration** & & & **Source** & **Concentration** \\  & **(gL\({}^{-1}\))** & & & **(mgL\({}^{-1}\))** & \\ \hline TiO\({}_{2}\) P25 & 1.0 & Philips HB 175 & 20 & 85\% in 120 min & [30] \\ TiO\({}_{2}\) & & Philips HB 175 & 20 & 63\% in 120 min & [30] \\ nanocrystal & & & 60 W & \\ TiO\({}_{2}\) & 1.0 & solar simulator & 100 & 95\% in 60 min & [31] \\ TiO\({}_{2}\) & & 1000 W & 10 & 95\% in 60 in & [31] \\ supension & 1.0 & sunlight & 10 & 95\% in 60 in & [31] \\ ZnO/TiO\({}_{2}\) & 0.5 & UV lamp & 20 & 80\% in 120 min & [32] \\ TiO\({}_{2}\) & & sunlight & 10 & 100\% in 200 min & [33] \\ TiO\({}_{2}\) & & & & & Present \\ nanoparticles & 0.3 & Hg lamp 300 W & 5 & 99\% in 40 min & work \\ - & - & sunlight & - & 75\% in 40 min & Present \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The comparison study of photodegradation efficiency of TiO\({}_{2}\) and TiO\({}_{2}\)-based composites at different experimental conditions for bentazon herbicide. Figure 5: Degradation efficiency of BZ at different pH values (**a**); absorption spectra of BZ in the presence of the TiO\({}_{2}\) photocatalyst under UV (**b**) and sunlight (**c**); degradation efficiency at different irradiation times for the TiO\({}_{2}\) photocatalyst of BZ (**d**).