## 2 Advanced Oxidation Processes
### Ozone-Based Technologies
#### 3.2.2 Catalytic and Photocatalytic Ozonation
In fact, the authors suggest that the Au-TiO\({}_{2}\) had low performance in photocatalytic ozonation due to a higher retention of photogenerated electrons related to its higher electronegativity, which could lower the generation of ozonide radicals, and, therefore, the generation of hydroxyl radicals [27]. Furthermore, Ag-TiO\({}_{2}\) has lower electronegativity, so its good performance could also be related to this fact, and this can explain why the presence of UVA did not have any effect on Au-TiO\({}_{2}\)[27]. In addition, in the study of [PERSON] et al. [27], TiO\({}_{2}\) also did not have any improvement when UVA was added, which could be related to poor photoactivity of the catalyst due to its high band-gap, while in the other doped catalysts, the results were better than the pure TiO\({}_{2}\) and without UVA, which means that UVA had a positive influence on them, maybe to their lower band-gap and high photoactivity [26,27]. [PERSON] et al. [103] had almost total removal using 10 mg/L for different synthesis methods of N-TiO\({}_{2}\) reaching TOD of 30-44 mg/L, and about 26-45 mg/L, for the different methods, using photocatalytic ozonation. These results were better than the ones provided by [PERSON] et al. [27], who used a catalyst doped with noble metals (best results for AgTiO\({}_{2}\) with TOD = 40 mg/L). This may suggest a good behavior of non-metal doping for photocatalytic ozonation, which may be interesting due to the costs associated with noble metals. Table 5 overviews works dealing with ozone-based technologies for parabens removal. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Pollutant** & **AOP** & **Catalyst** & \multicolumn{2}{c}{**Test**} & \multicolumn{2}{c}{**Results and**} & **Reference** \\ \hline  & & & & & **Conditions** & & **Conclusions** & **Reference** \\ \hline  & Photolytic & & & & & \(\bullet\) & Degradation of about 65\%, 70\%, \\  & ozonation & & \(\bullet\) & 5 mg/L of each & & 91\%, 94\%, 95\%, 100\%, and 100\% \\  & Photocatalytic & & & paraben in & & for O\({}_{3}\)/H\({}_{2}\)O\({}_{7}\)/Fe\({}^{2}\), & O\({}_{3}\)/H\({}_{2}\)O\({}_{2}\), \\  & & & & ultrapure water. & & O\({}_{3}\)/UV/H\({}_{2}\)O\({}_{2}\), O\({}_{3}\)/UV/TiO\({}_{2}\), \\  & Other ozone & & \(\bullet\) & UV radiation. & & O\({}_{3}\)/UV/H\({}_{2}\)O\({}_{2}\), O\({}_{3}\)/UV/TiO\({}_{2}\), \\  & techniques & & & & O\({}_{3}\)/UV/H\({}_{2}\)O\({}_{2}\)/TiO\({}_{2}\), and & \\  & & & & & O\({}_{3}\)/UV, respectively in 20 min. & \\ \hline  & & TIO\({}_{2}\) & \(\bullet\) & 10 mg/L of each & & \\  & & Au-TiO\({}_{2}\) & & paraben in & & \\  & & Ag-TiO\({}_{2}\) & & ultrapure water. & & \\  & and BeP & ozonation & Pd-TiO\({}_{2}\) & \(\bullet\) & 70 mg/L of catalyst. & & \\  & & & Pt-TiO\({}_{2}\) & & \(\bullet\) & 70 mg/L of catalyst. & \\  & & & Pt-TiO\({}_{2}\) & & \(\bullet\) & 70 mg/L of catalyst. & \\ \hline  & & TIO\({}_{2}\) & \(\bullet\) & 10 mg/L of each & \(\bullet\) & Photocatalytic ozonation led to \\  & & & Ag-TiO\({}_{2}\) & & paraben in & \\  & & & Ag-TiO\({}_{2}\) & & ultrapure water. & \\  & and BeP & Ozonation & Au-TiO\({}_{2}\) & & \(\bullet\) & 70 mg/L of catalyst & \\  & & & Pd-TiO\({}_{2}\) & & dose. & \\  & & & Pt-TiO\({}_{2}\) & & \(\bullet\) & UVA radiation. & \\ \hline  & & & & & \(\bullet\) & Photocatalytic ozonation \\  & & & & & & removed 96–98\% (\{\rm pH}=9) and \\  & & & & & 74–80\% (\{\rm pH}=3), while & \\  & & Photolytic & & & & & photoicity ozonation obtained \\  & & Ozonation & \(\bullet\) & 10 mg/L paraben & & 50–53\% (\{\rm pH}=3) and 53–65\% \\  & and BeP & Photocatalytic & & & & (pH = 9). & \\  & & Ozonation & & \(\bullet\) & UV radiation. & \\  & & & & & (15 min), and 65\% and 100\% \\  & & & & & & (45 min) for O\({}_{3}\) + UV and O\({}_{3}\) + \\  & & & & & & UV + ZnO, respectively. & \\ \hline  & & & & & \(\bullet\) & Photocatalytic ozonation led to \\  & & & & & mixture in \\  & & & & & ultrapure water.