## 5 Titanium Dioxide as a Photocatalyst for Water Remediation Applications
The amount of IBP removed from the ultra-pure water solution containing 1000 mg \(\times\) dm\({}^{-3}\) TiO\({}_{2}\) and 1.0 mg \(\times\) dm\({}^{-3}\) IBP after 1 h of treatment with artificial UV light was 92% with a total organic carbon (TOC) removal rate reaching 78%. During the study, it was found that artificial UV light was more beneficial for the process. Concentrations of TiO\({}_{2}\) used in the tests varied between 20-1000 mg \(\times\) dm\({}^{-3}\), whereas the 1000 mg \(\times\) dm\({}^{-3}\) concentration proved to be the optimal one. Various control studies were implemented including a direct photolysis test of IBP under solar irradiation. These tests showed that the natural photolysis rate for IBP was minimal under 10% after 1 h of irradiation, which is consistent with the state of knowledge regarding the stability of IBP under light exposure [47]. In the sample filled with spring water, the efficiency of photocatalysis was influenced by minerals present in the water and negatively impacted the overall process. The achieved degradation rate of IBP and TOC removal, in this case, were 60% and 45%, respectively. Regarding the ecotoxicological studies, the treated solutions were tested against _Daplmia similis_ and _Raplidocelis subcapitata_. Bioassays with _D. similis_ showed 30% immobilization after 48 h of exposure. Tests with _R. subcapitata_ at first showed ethanol growth for the samples after 5 and 10 min treatment followed by 40% growth inhibition for the sample after 45 min of treatment. The inhibitory effect gradually decreased with prolonged treatment of the solution. Thus, no inhibitory effect was observed in the sample after 120 min of treatment. The initial toxicity of IBP on these organisms was not tested [98]. In different studies, immobilized TiO\({}_{2}\) was applied in the UV light-induced photocatalytic degradation of three pharmaceuticals, namely, atenol (ATL), chlorpromazine (CPR), and metronidazoleae (MET) in a water solution [99]. In the study, pure anatase (>99% anatase, 8 nm crystallites) immobilized on ceramic plates by the sol-gel method was applied. After 8 and 16 h, the TOC removal rates reached 70% and 90%, respectively. Ecotoxicological tests were performed on _Spirodela polyrrhiza_ plants. The plants were grown in a medium containing 20 mg \(\times\) dm\({}^{-3}\) concentrations of each pharmaceutical without any prior photocatalytic treatment. Ecotoxicological assessments were made based on relative growth rate (RGR) and relative from number (RFN). They resulted in the death of all plants after 24 h exposure in an untreated pharmaceutical mixture. What is interesting is that _S. polyrrhiza_ exposed to the photocatalytically pre-treated mixture, retained their growth ability. Plants exposed to pharmaceutical solutions for 8 h revealed RGR and RFN loss of 28.57% and 30%, respectively, due to the presence of harmful intermediates in the mixture. Plants exposed to pharmaceutical solutions pre-treated photocatalytically for 16 h revealed no change in RFNand only a 2.37% loss of RGR. This observation proved that photocatalytic treatment of the pharmaceutical solution significantly reduced toxicity of the solution on tested plants [99]. In another study, a molecularly imprinted photocatalyst with low-TiO\({}_{2}\) loading was prepared for the degradation of different pharmaceuticals such as atorvastatin (ATR), diclofenac (DIC), ibuprofen (IBP), ticonazole (TCZ), valsartan (VAL), ketoconazole (KET), and gentamicin (GNT). The efficiency of photodegradation using a photocatalyst in non-imprinted systems and a commercial Degussa P25 TiO\({}_{2}\) were compared [100]. Molecular imprinting was undertaken to address one of the disadvantages of TiO\({}_{2}\), which is the low selectivity of heterogeneous photocatalysis to target contaminants. The molecularly imprinted systems were prepared by an acid-catalyzed sol-gel method using 150 mg sample of a pharmaceutical, 100 mg of TiO\({}_{2}\), and tetraethoxysilane (45 mmol) with the addition of 0.2 M HCl in the volume ratio of 1:2.