# 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
In particular, pH influences the surface charge of TiO\({}_{2}\), and thus organic pollutant adsorption, a step that markedly influences their photocatalytic degradation. The surface charge is related to the size of the particles. Generally, for P25 with a particle diameter \(\sim\)25 nm, the pH at the point of zero charge (pH\({}_{\text{PZC}}\)) is 6.9, which shifts to more basic values for smaller particles [42]. As adsorption of the target pollutants is a crucial step, the nature of the aqueous matrix is also important, due to the simultaneous presence of other species like carbonates, humic acids or dissolved gases, which may lead to competitive adsorption phenomena, lowering the final photocatalytic efficiency. The degradation of amoxicillin, ampicillin and coloxacillin antibiotics in water solution (Figure 4) under UV radiation (>300 nm) in presence of TiO\({}_{2}\) was higher at pH 11, whereas complete degradation was reached at pH 5 after addition of H\({}_{2}\)O\({}_{2}\)[43]. Different TiO\({}_{2}\) nanomaterials may have different adsorption capacities towards different pollutants. This has been clearly shown in a paper were the photocatalytic degradation (under simulated solar irradiation) of both delofibic acid and carbamazepine (two pharmaceuticals with different therapeutic effects) and of two contrast agents (iomeprol and iopromide) (Figure 5) was studied in aqueous  
Figure 4: Molecular structure of some antibiotics (**a**) Amoxicillin; (**b**) Ampicillin; (**c**) Cloxacillin. suspensions containing either P25 or Hombikat UV100 [44], whose textural properties are reported in Table 2.  
The results showed the better photocatalytic activity of P25 towards the degradation of clofibric acid and carbamazepine. Hombikat UV100 was instead more effective towards the degradation of iomeprol, likely due to a higher adsorption of the latter molecule at the surface of that solid. Possible degradation products were also identified and quantified: with clofibric acid, several aromatic and aliphatic degradation products were detected, and a possible multi-step degradation scheme was proposed (Figure 6). Moreover, a TiO\({}_{2}\) photocatalyst-based process showed a good ability to remove up to 68% chlorhexidine digluconate (CHD, an antiseptic compound), in 1 h at 25 \({}^{\circ}\)C with a substrate-to-catalyst ratio of 2.5:1 under UV light at basic pH [45]. When micro-pollutants like PPCPs are concerned, the use of high surface area TiO\({}_{2}\) may help their adsorption. In this respect, mesoporous TiO\({}_{2}\) can be obtained by different methods, including hard and soft templates and sol-gel methods [37]. Some works report the photocatalytic performance of mesoporous TiO\({}_{2}\) where the higher porosity and higher specific surface area should play a prominent role: for instance, Zr-doped mesoporous TiO\({}_{2}\) was tested for the degradation of ibuprofen and other (mainly anti-inflammatory) pharmaceuticals [46]. It was found that the material shows improved adsorption of the pollutants from the solution and high initial photocatalytic activity. In the adopted experimental conditions, however, the rapid formation of intermediates and of some polymeric compounds led to decreased activity in following cycles. pH was found to deeply affect the photocatalytic activity, which increased by a factor of six when pH decreased \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Characteristics** & **P25 (TiO\({}_{2}\))** & **Hombikat UV100** & **Mesoporous Titania (TiO\({}_{2}\))** \\ \hline Crystallographic phase (\(w/w\)) & \(75\pm 5\%\) anatase \(25\pm 5\%\) rutile & 100\% anatase & 100\% anatase \\ Diameter of particles (nm) \({}^{*}\) & \(15\pm 30\) & \(<\)10 & \(<\)20 \\ Specific surface area (BET area, m\({}^{2}\)g\({}^{-1}\)) & \(60\pm 10\) & \(>\)250 & 150 \(\pm\) 40 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: General textural properties of TiO\({}_{2}\)-based photocatalysts. * particles size based on TEM images and/or Scherrer calculation. Adapted from [44].