## 3 Results
### Photocatalytic Activity in Toluene Oxidation  
In order to evaluate the photocatalytic activity of the obtained metal titanate nanorods ATiO\({}_{3}\), toluene was employed as target pollutant [77]. The photodegradation reaction in gas phase was illumination by light-emitting diodes (LEDs). At the present time, traditional incandescent lamps are displaced by LEDs in many applications, due to much higher efficiency in light electricity conversion. In addition, benefits deriving from the implementation of LEDs result from the small dimensions and are long lasting. Therefore, the research has been extended with photodegradation experiment of toluene in the presence of ATiO\({}_{3}\) under the influence of 1 h irradiation emitted by LEDs with \(\lambda_{\text{max}}\) = 375 nm and \(\lambda_{\text{max}}\) = 400 nm, respectively. The blank experiment was carried out to control the losses of toluene with the presence of irradiation and without photocatalysts. To exclude the effect  
Figure 7: PL spectra of metal titanate nanorods ATiO\({}_{3}\) (A = Mg, Co, Ni, Zn) upon 330 nm excitation.  
of toluene adsorption at the surface of the photocatalyst, the amount of adsorbed toluene was measured during 30 min without light irradiation before every experiment.  
The results showed that 5% of toluene was decreased after 30 min, indicating the photolysis of toluene. The photocatalytic activity of ATiO\({}_{3}\) is presented in Figure 8. Based on the obtained results after 60 min of irradiation, it can be concluded that all of the samples presented toluene photodegradation. Under LEDs illumination with \(\lambda_{\text{max}}\) = 375 nm, the highest toluene degradation rate is 41% in presence of NiTiO\({}_{3}\) compared to the other nanomaterials which varies from 24 to 29%. So, the photocatalyst NiTiO\({}_{3}\) exhibits the highest photocatalytic activity under \(\lambda_{\text{max}}\) = 375 nm because of the low recombination rate which is shown at the PL results. In case of a longer irradiation wavelength (\(\lambda_{\text{max}}\) = 400 nm), better photocatalytic activity was obtained. The highest efficiency (62%) of toluene degradation was observed for ZnTiO\({}_{3}\) compared to the other nanomaterials which varies from 28 to 36%.  
The photocatalytic reaction rate constant (\(k\)) is used to evaluate the photocatalytic activity, which is calculated by the formula ln (C\({}_{\text{O}}\)/C\({}_{\text{(t)}}\)) = \(k\)t, where C\({}_{\text{O}}\) and C\({}_{\text{(t)}}\) being the initial and reacted concentration of toluene at time t, respectively. According to these kinetic studies, the photocatalytic reaction rate constants are presented in Table 3. Particularly worth mentioning the constant in the case of ZnTiO\({}_{3}\) under LED illumination with \(\lambda_{\text{max}}\) = 400 nm is 16.08 \(\times\) 10\({}^{-3}\) min\({}^{-1}\) and particular of interest the constant in case of NiTiO\({}_{3}\) under LED illumination with \(\lambda_{\text{max}}\) = 375 nm is 9.21 \(\times\) 10\({}^{-3}\) min\({}^{-1}\).  
The photoactivity per mass (%/mg) of every photocatalyst is calculated in Table 4. The results nominate the presented photocatalytic results and that ZnTiO\({}_{3}\) exhibits 15.1%/mg toluene degradation which is the best photocatalytic activity per mas  
Figure 8: Toluene decomposition under LED irradiation (**a**) \(\lambda_{\text{max}}\) = 375 nm and (**b**) \(\lambda_{\text{max}}\) = 400 nm of metal titanate nanorods ATiO\({}_{3}\) (A = Mg\({}_{\text{C}}\), Co, Ni, Zn).  
\begin{table}
\begin{tabular}{c c c} \hline
**Photocatalyst** & \(k\) **(10\({}^{-3}\) min\({}^{-1}\)) under \(\lambda_{\text{max}}\) = 375 nm** & \(k\) **(10\({}^{-3}\) min\({}^{-1}\)) under \(\lambda_{\text{max}}\) = 400 nm** \\ \hline NiTiO\({}_{3}\) & 9.21 & 7.44 \\ MgTiO\({}_{3}\) & 4.43 & 5.47 \\ CoTiO\({}_{3}\) & 5.59 & 5.72 \\ ZnTiO\({}_{3}\) & 5.37 & 16.08 \\ \hline \end{tabular}
\end{table}
Table 3: Photocatalytic reaction rate constants under LED illumination of metal titanate nanorods ATiO\({}_{3}\) (A = Mg, Co, Ni, Zn).