## 5 Titanium Dioxide as a Photocatalyst for Water Remediation Applications  
Initially, TiO\({}_{2}\) was tested for applications in solar energy production. Later on, the studies evolved into environmental photocatalysis [55]. Titanium dioxide and its various modifications have been considered for applications in water remediation. In previous sections, we discussed the pros and cons of this material in depth. As a result of these, the most significant efforts have been targeted at research making TiO\({}_{2}\) an appropriate catalyst for photodegradation of common water contaminants including emerging contaminants. Most compounds belonging to this group are stable APIs that are difficult to remove from aqueous solutions. TiO\({}_{2}\) is not the sole material used for this application, and there are many alternatives among metal oxide nanoparticles and other materials such as quantum dots, which have found use in the photocatalysis of pharmaceutical water contaminants. [PERSON] et al. summed up these applications in their review that covered a broad selection of nanophotocatalysts for biomedical wastewater management [95]. Apart from pharmaceuticals, substances used in agriculture also belong to emerging contaminants and pose a significant threat when entering the environment in a non-regulated manner (Figure 5). In agriculture, TiO\({}_{2}\) NPs were applied in photocatalytic degradation of heterocyclic organic pollutants such as diazinon and imidalcoprid, which are used as insecticides. The risk posed by these chemicals is associated with the fact that they can be washed from the soil into waterways, effectively contaminating the soil and rendering it unusable, or worse, posing a threat to human health if the pollutant enters drinking water supplies [96]. The  
Figure 5: The applicability of TiO\({}_{2}\) as a catalyst in the photodegradation studies of various insecticides in agriculture, pharmaceutically active ingredients, and selected organic compounds including dyes. results of the photocatalytic tests with titania indicated a 99% decrease in the initial concentration of 0.13 mM diazinon dissolved in 5 dm\({}^{3}\) of water after 100 min of irradiation with 287 nm UV light in the presence of H\({}_{2}\)O\({}_{2}\). The authors stated that this rate could only be achieved with an optimal concentration of H\({}_{2}\)O\({}_{2}\). Too low or too high concentrations could negatively impact the process of photocatalytic degradation. Moreover, it was found that H\({}_{2}\)O\({}_{2}\) could promote the generation of OH radicals, and also, in abundance, it might act as a OH scavenger or react with TiO\({}_{2}\), forming peroxo-compounds. Conversely, it was found that 0.22 mM imidalcoprid solution in 5 dm\({}^{3}\) of water was almost completely degraded using immobilized nanoparticles of titania after 90 min of irradiation with 267 nm UV light in the presence of H\({}_{2}\)O\({}_{2}\)[96]. The ever-growing worldwide use of drugs corresponds with higher contamination of the environment, especially water. This is a significant concern and a challenge for modern society. With regard to the degradation of pharmaceutical pollutants in water, TiO\({}_{2}\) has been used thus far to catalyze photodegradation of drugs belonging to classes such as antibiotics, analgesics, anticonvulsants, \(\beta\)-blockers, lipid regulators, non-steroid anti-inflammatory drugs (NSAIDs), psychiatric drugs, and many more [97]. One of the studies on the matter presented an application of TiO\({}_{2}\) for the degradation of ibuprofen (IBP) in water paired with an ecotoxicological analysis of such a solution [98]. Researchers used artificially contaminated ultra-pure water as well as spring water. Tests were performed under artificial and natural UV light produced with a 125 W medium-pressure Hg vapor lamp, and the total radiation equaled 110.67 J \(\times\) cm\({}^{-2}\).