# Nanomaterials for the Abatement of Pharmaceuticals and Personal Care Products from Wastewater
## 4 Removal of PPCPs by Non-Conservative Methods Envisaging the Use of Nanomaterials
### Photocatalysis and Other Advanced Oxidation Processes
Figure 5: Molecular structure of two contrast agents: (**a**) Iomeprol; (**b**) Iporomide. from nine to two. According to the authors, the presence of surface Zr led to a more hydrophobic material, with a higher affinity of non-polar molecules. Ibuprofen is a weak acid (pKa = 4.4) and at low pH mostly occurs as undissociated molecules that can absorb at the surface by H-bond through carboxylic groups. The (more hydrophilic) intermediates formed were instead desorbed. On the spur of the growing interest in the production of solar fuels, there is an increased interest in developing solar photocatalysis also for the removal of pharmaceuticals, and several works report on the use of (natural or simulated) solar radiation for the removal of pharmaceuticals. To this respect, the photocatalytic degradation under sunlight of a common antibiotic (linomycin) was studied in the  
Figure 6: **(a)**: Suggested simplified degradation scheme of the photocatalytic degradation of clofibric acid (Bold: identified intermediates) and (**b**) example for possible oxidative and reductive reaction pathways of clofibric acid. Reproduced with permission from [44], Copyright Elsevier Ltd., 2003.  
presence of P25 [47]. A hybrid system (consisting of a solar photoreceptor coupled with a membrane module, used to confine both photocatalyst and pollutants in the reaction environment) was used as a pilot plant (Figure 7). The antibiotic was successfully oxidized and the hybrid system resulted to be particularly useful for that application. The hybrid system allowed the simultaneous separation of the photocatalyst particles and of limomycin and its degradation products from the permeate flow; indeed, the membrane rejection for those species was quite high. The analyses of the data collected by using the hybrid system, both in total recycle and in continuous regime, indicated that the presence of the membrane allows reducing the amount of both the substrate and intermediates to very low concentration levels. This shows that the engineering of the photocatalytic system will play a prominent role in the future, in order to allow an effective removal of such pollutants. A hybrid UV/TiO\({}_{2}\)/O\({}_{3}\) approach was adopted for the disposal of fluoxetine [48] and norfluoxetine. The former is the active principle of Prozac\({}^{\text{B}}\), the latter is its main metabolite. Both are non-biodegradable and recalcitrant pharmaceutical products, which may be found in surface waters after therapeutic use. Since current wastewater treatments are unable to remove them completely, a hybrid approach was tested, with O\({}_{3}\)/H\({}_{2}\)O\({}_{2}\) as oxidants and TiO\({}_{2}\) as photocatalyst. In the same papers, other approaches were also tested. In all the experiments, a strong pH dependence of the degradation of fluoxetine was found. When Degussa P25 was adopted as a photocatalyst, the drug adsorption at the surface of TiO\({}_{2}\) NPs played an important role, in that the drug adsorption was enhanced at alkaline pH, whereas mass transfer problems occur at acidic pH (where both the drug and the TiO\({}_{2}\) surface are protonated). A similar result was observed by some of us when the adsorption of negatively charged species on mesoporous TiO\({}_{2}\) were studied [49; 50]. From an economic point of view, however, many papers concluded that in the case of drugs, homogeneous photocatalysis has a lower environmental impact as compared to heterogeneous processes. To this respect, the degradation of \(\alpha\)-methylphenylglycine, a common precursor of pharmaceuticals, often chosen as an aromatic amino acid model molecule because of its high water solubility and its non-biodegradable character, has been studied by means of solar photo-Fenton and TiO\({}_{2}\) photocatalytic degradation [51; 52]. Solar photo-Fenton (combined with biological systems) is also adopted to treat wastewaters that contain pharmaceuticals. In the paper, solar photo-Fenton was more effective in the degradation, due to a higher degradation rate.