# Photocatalytic Degradation of Selected Non-Opioid Analgesics Driven by Solar Light Exposure
## 3 Results
### Photocatalysis and Photoelectrocatalysis--Systems with Tungsten Oxide and Iron Oxide
#### 3.2.1 Application of WO\({}_{3}\) and Fe\({}_{2}\)O\({}_{3}\) Used Individually  
No significant changes were observed in the area of the signals for paracetamol and ibuprofen during the process under the solar lamp radiation with WO\({}_{3}\) (Figure 2). As no new signals in the chromatograms recorded for these compounds were observed (Figure S1), the decomposition process probably does not occur under the applied conditions. The process of photodecomposition of naproxen most likely occurs, but with very low efficiency. The small additional signals were observed for this drug; however, their intensity during a prolonged time of radiation did not change significantly (Figure S1). Only for ketoprofen, after 90 min of irradiation, a 40% decrease in the analyte content was observed. For ketoprofen, the formation of two additional signals was observed after 15 min of irradiation, but the intensity of the main peak changed slightly. Figure 2a summarizes the recorded changes in detected pharmaceuticals over time during solar lamp radiation with WO\({}_{3}\). Similar relationships were observed in the case of the photoelectrocatalytic processes of the studied compounds (Figure 2b). In the case of ketoprofen using photoelectrocatalysis, three additional signals were obtained, the intensity of which increased with the extended exposure time (Figure S1B). Two of the peaks had the same retention time as the signals obtained in the photocatalysis process (t\({}_{\text{R}}\) = 3.1 min and t\({}_{\text{R}}\) = 3.25 min) and identical UV spectra. However, a third new signal with a retention time of 2.9 min may suggest that the mechanism of degradation of this compound is slightly different. [PERSON] et al. reported that ketoprofen was not degraded during a sun irradiation cycle of 5 h using colloidal WO\({}_{3}\) thin film [52]. It was explained by the electrostatic repulsion between the negative charge of ketoprofen at pH 6 and the negatively charged WO\({}_{3}\) surface. The application of the electric bias was successful in promoting a 50% decomposition of this drug after irradiation for 5 h, with a degradation rate constant of 0.22 h\({}^{-1}\)[52]. In our study, the rate constant of ketoprofen decomposition in the photocatalytic process was 0.040 min\({}^{-1}\), which in photoelectrocatalysis was 0.0165 min\({}^{-1}\) in the examined time range. The solar photocatalytic process was also carried out for ketoprofen and naproxen, using a larger active surface of the photocatalyst. The WO\({}_{3}\) immobilized on the FTO plate (4 \(\times\) 1.5 cm) was immersed in 10 mL of the standard solution and placed in a quartz vessel. Next, the solution was irradiated with solar radiation for 4 h. The obtained chromatograms are present in Figure S2. After 15 min of the process, a decrease in the intensity of the signal for ketoprofen was observed, and 50% of the analyte was decomposed after 30 min  
Figure 2: Decomposition of the tested compounds with WO\({}_{3}\) (active area 0.28 cm\({}^{2}\)) under solar lamp radiation over time: (**a**) photocatalysis; (**b**) photoelectrocatalysis (oxidation potential of +1.2 V). (Figure S2). The formation of 3 intermediates was also recorded on the chromatogram. The intensity of the first two additional signals increased during the first hour of irradiation of the sample, and after that time, the decomposition products were also degraded. For the third decomposition product, an increase in signal intensity was observed during the entire photodecomposition process. Under the presented measurement conditions, high process efficiency was achieved--after 4 h, the surface area of the signal for ketoprofen decreased by 97% (Figure 3a). A large increase in degradation efficiency was also observed for naproxen. After 15 min of irradiation of the sample, there was a slight decrease in the intensity of the signal for naproxen, and a small additional signal appeared.