# Photocatalytic Degradation of Selected Non-Opioid Analgesics Driven by Solar Light Exposure
## 3 Results
### Effect of the Matrix  
For ketoprofen, the influence of the matrix on the photodegradation process with the use of photocatalysis was investigated. A sample of river water spiked with ketoprofen (10 mg/L) was acidified with nitric acid to pH 2, and next was irradiated with a solar lamp in the presence of WO\({}_{3}\) with an active surface area of 6 cm\({}^{2}\) for 4 h. A similar degradation process proceeded in ultrapure water. Just after 15 min, three new signals appeared on the chromatogram (Figure 5a). The intensity of those recorded at t\({}_{\text{R}}\) = 3.9 and 4.1 min gradually increased up to 60 min and then decreased, but the intensity of the new signal obtained at t\({}_{\text{R}}\) = 4.3 min grew all the time. After 30 min of irradiation, about 50% of this drug degradation was achieved, and after 4 h of the process, the complete disappearance of the signal for the analyte was observed (Figure 5a). Figure 4: Decomposition of the tested analytes with WO\({}_{3}\)/Fe\({}_{2}\)O\({}_{3}\) hybrid photocatalyst (active area 0.28 cm\({}^{2}\)) under solar lamp radiation over time: (**a**) photocatalysis; (**b**) photoelectrocatalysis (oxidation potential of +1.2 V). [PERSON] et al. found a much slower degradation of the ketoprofen in wastewater effluent (DOC = 3.3 mg/L, pH 7.5) compared to pure water using solar light and a photocatalyst containing TiO\({}_{2}\) in combination with a strong oxidant (Na\({}_{2}\)S\({}_{2}\)O\({}_{8}\)) [55]. The authors explained the obtained results through the presence of dissolved salts and organic carbon, which noticeably slows down the efficiency of the treatment. To obtain more information about the reactive species in charge of the photodegradation of ketoprofen, suite quenchers were utilized to scavenge the reactive species. Here, 1 mM (EDTA) was used as a hole (h\({}^{+}\)) scavenger; the availability of electrons is expected to increase, allowing the formation of \({}^{\bullet}\)O\({}_{2}\). In the opposite, 1 mM KBrO\({}_{3}\) was utilized as an electron scavenger, inhibiting the reduction of O\({}_{2}\) into O\({}_{2}\) radicals participating in degrading ketoprofen. Additionally, isopropyl alcohol (1 mM) was utilized to catch \({}^{\bullet}\)OH. It was noted that the addition of EDTA (h\({}^{+}\) scavenger) resulted in somewhat sluggish KET photodegradation, displaying that the holes (h\({}^{+}\)) are not an important reactive species in this process. When KBrO\({}_{3}\) was utilized as an electron (e\({}^{-}\)) entrap, the photodegradation of KET dropped around 20%, implying that the electron (e\({}^{-}\)) played a meaningful role in the degradation of KET. On the other hand, by introducing isopropyl alcohol (\({}^{\bullet}\)OH scavenger), the photodegradation efficiency decreased by around 22%, indicating that \({}^{\bullet}\)OH was also the main species that supported the photodegradation of KET. Based on these outcomes, it can be figured out that \({}^{\bullet}\)OH radicals and electrons (e\({}^{-}\)) are the major reactive species during the photodegradation of KET. Moreover, from a mechanistic point of view, an important issue is known: the formation of intermediate species when photocatalysts are used for the photodegradation of KET. In the case of the presence of isopropyl alcohol, three major additional signals associated with intermediate products of photodegradation KET on the chromatogram appeared at retention times of 4.4, 4.2, and 3.9 min, alongside the peak of KET situated at 4.8 min. The intensity of two of them (tr = 4.2 and 3.9 min) decreased over time, while the signal with tr = 4.4 min increased. During degradation (after 20 min), three new additional signals with low-intensity signals with tr = 3.4, 2.9, and 2.7 min appeared. Similar chromatograms were obtained for the sample with the addition of KBrO\({}_{3}\), but the peaks had different intensities. However, for the sample with EDTA, no signal at tr = 4.2 min was observed, and the peak at retention time of 4.4 min was larger (Figure S5).