## 5 Titanium Dioxide as a Photocatalyst for Water Remediation Applications
Titania was added 2.5 h after the reaction had been initiated. Later, the template was removed by slow heating. First, the drugs were tested for their ability to photolyze. The tests showed an average degradation rate of 5.6% for all tested substances under irradiation without a photocatalyst, which was considered negligible. Experimental samples containing 50 cm\({}^{3}\) of the pharmaceutical and 33 mg of the photocatalyst were placed into a bath reactor with airflow (6.5 cm\({}^{3}\)\(\times\) s\({}^{-1}\)). The rate of photocatalysis was evaluated at two points: (1) 1 h incubation of a pharmaceutical in the reaction solution for initial adsorption to the system; and (2) degradation stage under UV irradiation (125 W Hg vapor lamp, 45 W \(\times\) m\({}^{-2}\)). In the case of molecularly imprinted systems, it was observed for all tested drugs that the photocatalytic performance was enhanced in contrast to non-imprinted systems and bare P25 TiO\({}_{2}\). It was found that the imprinted systems revealed higher degradation efficiencies by the margin of 5-427% than their bare counterparts. The increase in performance was explained by the presence of cavities selective toward the tested pharmaceuticals. These sites enhanced interactions between the drugs and TiO\({}_{2}\). Additionally, in the recycling tests with diclofenac, the system retained 60% of its initial photocatalytic activity after seven catalytic cycles [100]. In a different study, a TiO\({}_{2}\) system was used for the removal of antipyrine (AP) by photodegradation in spinning disk reactors [101]. The disks were made of glass and imprinted with TiO\({}_{2}\) through a sol-gel method. It was noted that under optimal conditions, AP degraded completely after 120 min of irradiation. Additionally, no loss of efficiency of the photocatalytic disks was observed, even after 10 cycles. The photocatalyst was tested for its dark activity, but no change in AP concentration was noted. After the addition of H\({}_{2}\)O\({}_{2}\), molecular degradation reached 12.6% of the initial AP concentration. In the UV irradiation test, AP was removed 76.4% in 120 min. UV/H\({}_{2}\)O\({}_{2}\) and UV/H\({}_{2}\)O\({}_{2}\)/TiO\({}_{2}\) systems reached 93% and 95.9% degradation rates of AP, respectively. Analysis with neural network simulations proved that the initial concentration of H\({}_{2}\)O\({}_{2}\) had the greatest impact on the efficiency of the reaction, and its optimal concentration was found to be at 1500 mg \(\times\) dm\({}^{-3}\)[101]. Photocatalytic systems based on P25 TiO\({}_{2}\) immobilized on lime glass were studied by [PERSON] et al. for heterogeneous catalysis of a number of pharmaceuticals and personal care products such as hydrocarbons (HCR), 178-estradiol (ESR), verapamil (VRP) and three paraben derivatives (PB): methyl- (MePB), ethyl- (EtPB), and propyl- (PrPB) [102]. The concentration of the contaminants varied in these tests, ranging from 1 \(\times\) 10\({}^{-4}\) to 2 \(\times\) 10\({}^{-4}\) mol \(\times\) dm\({}^{-3}\) for VRP, HCR, and PB while ESR was prepared as a saturated solution at 25 \({}^{\circ}\)C. After 2 h of irradiation, only 6% of the initial concentration of HCR remained in the sample with a TOC mineralization rate of 69%. For ESR, almost the entirety of the drug was photodegraded, leaving only 2% of the initial ESR concentration in the sample with a 32% TOC removal rate. Degradation tests of VRP revealed that 18% of the initial concentration remained in the sample after 2 h of irradiation, and the achieved TOC removal rate was at 18%. PB derivatives seemed to be quite resistant to photocatalysis, especially MePB, which had a three times lower degradation rate compared to other PB derivates. For MePB, 2 h of irradiation led to 20% reduction only in the amount of substrate, while for the same irradiation time, around 50% of EtPB and PrPB was degraded. One of the main aims of the study was to compare the results of homogeneous catalysis with ferric ions and heterogeneous catalysis with titania.