# 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  
According to the literature, the non-conservative methods that are actually able to efficiently remove PPCPs are mainly based on advanced oxidation processes (AOPs). AOPs generally imply the in-situ production of highly reactive species (i.e., H\({}_{2}\)O\({}_{2}\), OH-, O\({}^{-}\), O\({}_{3}\)) that allow the degradation of refractory organic pollutants into biodegradable compounds. Rather than stand-alone methods, AOPs are really effective when used either before or after biological treatments. AOPs may imply the use of nanomaterials (NMs) as either catalysts or photocatalysts, which improve the selective removal of the target pollutant [35; 36]. As far as PPCP removal by AOPs is concerned, mineralization of the PPCPs is not necessarily achieved, with a consequent release into the environment of by-products that are indeed more biodegradable (and less toxic) than the original drug. In those cases, a biological post-treatment step may be feasible. The most suitable AOPs for PPCP removal are heterogeneous photocatalysis, ozonation and Fenton (or Fenton-like) reaction. While the first surely implies the use of NMs (like photocatalytic nanoparticles or nanoporous materials), the other two may not. A photocatalyst is a semiconductor where electrons are promoted from the valence band (VB) to the conduction band (CB), after absorbing photons with higher energy than the semi-conductor band gap energy (Figure 3). Photocatalysts can be activated by either simulated or natural light. The generated holes (h\({}^{+}\)) can either oxidize adsorbed water molecules (or OH\({}^{-}\) ions) and produce OH radicals or directly oxidize the adsorbed contaminants. The electrons transferred to the conduction band can react either with oxygen (O\({}_{2}\)) dissolved in water (forming a superoxide radical ion O\({}_{2}^{-}\)) or directly with the contaminant at the surface. The reaction efficiency is driven by catalyst concentration, pH, water composition, wavelength and intensity of radiation. As a photocatalyst, TiO\({}_{2}\) is inexpensive, non-toxic, photochemically stable and commercially available in several crystalline forms and with different particle sizes and morphologies. Moreover, by different methods, it is also possible to obtain TiO\({}_{2}\) with a high surface area and relatively large pores, allowing a facile reactant/product diffusion [37]. TiO\({}_{2}\), and in particular Degussa P25 (hereafter referred to as P25) is universally considered one of the most efficient photocatalysts for the abatement of several pollutants including PPCPs, followed by ZnO. The superior photocatalytic performance of P25 is mostly ascribed to the peculiar physico-chemical features of its crystallites, where the two crystalline phases anatase and rutile occur in an 80:20 weight ratio [37]. The peculiar nanostructure of P25 favors the electron/hole separation, lowering their recombination frequency. Figure 3: Sketch of a photocatalytic nanoparticle under illumination. The behavior of ZnO was even more promising in the case of the photocatalytic abatement of sulfamethazine (an antibacterial agent) [38] and of the antibiotic chloramphenicol [39]. ZnO also showed good ability to completely degrade the ABs amoxicillin, ampicillin and coloxacillin in 3 h with a chemical oxygen demand (COD) and a dissolved organic carbon (DOC) removal of 23.9% and 9.7% respectively [40]. ZnS nanoparticles were applied as a photocatalyst to remove some \(\beta\)-lactam antibiotics with a degradation yield of 82-100% in 2 h at pH 4.5 [41]. As far as TiO\({}_{2}\) water suspensions are concerned, some parameters like the pollutant concentration, pH, light wavelength and intensity, the addition of other oxidants (like H\({}_{2}\)O\({}_{2}\)) and the type of water matrix are crucial.