## 2 Advanced Oxidation Processes
### Sonochemical Methods
#### 3.1.2. Parabens Abatement by Photocatalysis
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Pollutant**} & \multicolumn{2}{c}{**Test**} & \multicolumn{2}{c}{**Results and**} \\  & \multicolumn{2}{c}{**Conditions**} & & **Conclusions** & **Reference** \\ \hline \multirow{8}{*}{MP, EP and BuP} & \multirow{8}{*}{\(\bullet\)} & \multirow{8}{*}{UV radiation (254 nm).} & \(\bullet\) & Degradation of 77.2\%, 88\% and 96.3\% in 90 min and 79.9\%, & \\  & & & 95.2\% and 99.8\% of MP, EP and & \\ \cline{1-1}  & & 0.3 \(\times\) 10\({}^{-3}\) mol/L single & & BuP in 120 min. & \\ \cline{1-1}  & & & & Water matrix: EP removal of 88\%, 61.8\% and 37.9\% in 90 min & \\ \cline{1-1}  & & & & for ultrapure water, tap water & \\ \cline{1-1}  & & & & and wastewater, respectively. & \\ \hline \multirow{2}{*}{EP and BuP} & \multirow{2}{*}{\(\bullet\)} & \multirow{2}{*}{UVA radiation.} & \multirow{2}{*}{\(\bullet\)} & Degradation: \textless{}5\% in 24 h. & [95] \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._abatement in 30 min, using 1 mg/L of EP and 0.25 g/L of catalyst with a solar simulator as a radiation source. Although the experiments present several differences, these studies led to interesting results using solar radiation or solar simulated radiation, which should encourage more studies using these catalysts with the sun as a source of light. Furthermore, the study of [PERSON] et al. [96] suggests a better performance of ZnO over the traditional titanium dioxide. Several authors such as [PERSON] et al. [91], [PERSON] et al. [34], and [PERSON] et al. [97] experimented with doped TiO\({}_{2}\) catalysts in parabens abatement. [PERSON] et al. [34] tested Al-TiO\({}_{2}\), which had the best PP removal using a catalyst dose of 1 g/L with 95% abatement in 90 min, while [PERSON] et al. [97] used N-TiO\({}_{2}\) getting EP abatement of 32% and 13% in 240 min for N-TiO\({}_{2}\) and TiO\({}_{2}\) with Vis radiation, while solar radiation was used for 10 min and achieved about 34% and 43% for TiO\({}_{2}\) and N-TiO\({}_{2}\), respectively, for the best calcination temperature. In fact, the use of N-TiO\({}_{2}\) seems to enhance the parabens degradation under visible or solar radiation compared to pure TiO\({}_{2}\). Although the experiment by [PERSON] et al. [34] achieved almost complete removal, the authors did not perform experiments with pure TiO\({}_{2}\), and say that the presence of Al did not considerably change the band-gap energy. Moreover, for the best Al-TiO\({}_{2}\) (0.04 Al w%), the band-gap energy was about 3 eV, while the common TiO\({}_{2}\) catalyst usually has about 3.2 eV. This may suggest that Al it is not advantageous to make titanium dioxide more efficient under Vis or solar radiation. [PERSON] et al. [34] used 1 g/L of catalyst and initial PP dose of 0.42 mg/L, and [PERSON] et al. [97] used 0.5 g/L of catalyst and 0.3 mg/L of EP, while [PERSON] et al. [91] used 0.07 g/L of catalyst, 10 mg/L of each paraben (MP, EP, PP, BuP, and BeP), and UVA radiation. In [PERSON] et al. 's [91] study, they used a mixture with higher parabens concentrations and had lower catalyst concentration, but obtained removals of about 35-70%, 40-48%, 25-40%, 5-15%, and 1-10% for Pd, Ag, Pt, Au, and pure TiO\({}_{2}\), respectively, after 180 min. In this work, the presence of metals enhanced the degradation when compared to bare TiO\({}_{2}\), and Pd and Ag catalysts had better performance than the one obtained by [PERSON] et al. [97] using Vis radiation. In fact, the use of these noble metals seems to enhance the photocatalytic activity of titanium dioxide, which the authors suggest may be related to the electron charge transfer from the CB to the metallic nanoparticles band, less electron-hole recombination, or higher hydroxyl radical's production. The authors did not determine the catalysts' band-gap energy, but studies have shown where the deposition of metals could lower the catalyst band-gap energy.