## 2 Advanced Oxidation Processes
### Sonochemical Methods
#### 3.1.2. Parabens Abatement by Photocatalysis
However, the presence of noble metals should increase the catalysts' price, since these metals are usually expensive, so the N-TiO\({}_{2}\) may probably be more economically attractive, and it also showed good results under Vis and sunlight. Nevertheless, more tests using different concentrations and/or mixtures should be performed to confirm this theory. Other catalysts have also been investigated for the same purpose. [PERSON] et al. [6] tested single and mixture degradation of three parabens (MP, EP, and PP) using TiO\({}_{2}\) P25 and metal-free, graphite-like carbon nitride as catalysts with 417 nm radiation provided by LEDs. The GNC-500 catalyst had better performance, with about total removal in 20 min for single parabens and 99% removal for parabens mixture in 25 min. TiO\({}_{2}\) P25 only had total removal after 120 min for both experiments. [PERSON] et al. [33] removed single MP, EP, PP, and BuP by photocatalysis using I\({}_{x}\) -Bu\({}_{4}\)O\({}_{5}\)Br\({}_{2}\) as a catalyst, leading to a higher PP removal of 94.5% for I\({}_{0.7}\)-Bu\({}_{4}\)O\({}_{5}\)Br\({}_{2}\) in 60 min. The authors used >420 nm radiation, 1 g/L of catalyst, and 10 mg/L initial concentration of each paraben. In fact, this catalyst led to better abatement and had 2.51 eV, although not being the catalyst with lower band-gap energy (I\({}_{1}\)-Bu\({}_{4}\)O\({}_{5}\)Br\({}_{2}\) with 2.41 eV that led to 91.2%). Furthermore, [PERSON] et al. [98] achieved a better EP removal value of 97.6%, using CuO\({}_{0.75}\)/BiVO\({}_{4}\), by photocatalysis in 60 min, when the catalyst dose was 0.5 g/L and the paraben concentration was 0.5 mg/L, using a solar simulator as a radiation source (>280 nm). [PERSON] et al. [99] used Fe\({}_{3}\)O\({}_{4}\)/BiVO\({}_{4}\) heterostructure (bandgap of Fe\({}_{3}\)O\({}_{4}\) of 2.57 eV and of BiVO\({}_{4}\) of 2.36 eV) for MP abatement, reaching 75% of degradation in 60 min, with 0.1 g/L of catalyst and 5 mg/L of MP using solar light. These studies suggest interesting results for different catalysts compared to the traditional semiconductors, which may be also an option in the application of photocatalysis. Moreover, some of these catalysts present lower bandgaps than the traditional TiO2, which may be mainly responsible for the good results using radiation such as solar, simulated solar, or Vis light. Thus, this can be an advantage for the use of natural light and simplify the industrial implementation powered by the sun. The use of catalysts in powder form makes photocatalysis implementation and catalyst use difficult at an industrial level. This drawback can be overcome using powder catalyst immobilized in a support material, which can allow a good recovery and easy separation of the solid material from the reactional medium. With this, several supported and innovative catalysts have already been used, even for parabens degradation. [PERSON] et al. [58] tested TiO2 nanotubes (NT) arrays for photocatalytic degradation of paraben's mixture. In general, the catalyst presence improved the pollutants' degradation, but only 20% of removal was achieved in 60 min reaction, with 7 TiO2/NT plates and UVA. The maximum degradation was 25% when 14 plates were used. The usage of solar radiation enhanced the parabens mixture degradation compared to UVA, allowing a maximum parabens degradation of 80% using seven plates, although the operational installation was different. Furthermore, [PERSON] et al. [100] used photocatalysis catalyzed by nanostructures (titanate nanowires (TNW) and modified titanate nanowires with Mn) for MP removal in 90 min. The initial pollutant concentration was 10 mg/L, and the technology removed 62%, 50%, and 40% for Mn-doped TNW, Mn-adsorbed TNW, and single TNW, respectively, using UV-Vis (40-48% UV and 40-43% Vis). The use of these types of structures seems to allow good removal rates, combining also important advantages for industrial application. [PERSON] et al.