# Photocatalytic Degradation of Selected Non-Opioid Analgesics Driven by Solar Light Exposure
## 3 Results  
### UV Photodegradation  
Before the study of photocatalytic degradation of tested compounds, preliminary experiments were conducted using photolysis under UV light, and the results are presented in Figure 1. No significant changes were observed in the chromatograms obtained for paracetamol and ibuprofen after UV photodegradation. It indicated that these drugs were not degraded. Negligible photodegradation of paracetamol under UV irradiation was also reported in previous studies [45; 46]. Only H\({}_{2}\)O\({}_{2}\) hydrolysis was able to destroy the aromatic ring of the substrate with a partial conversion of the initial carbon content into carbon dioxide with 40% efficiency [42]. In the early oxidation stages, HPLC analysis showed the presence of 2-hydroxy-4-(N-acetyl)-aminophenol as the main intermediate. Longer reaction times give a broad spectrum of products. [PERSON] et al. found that paracetamol degradation during UV irradiation was almost entirely due to the photoactivity of the used TiO\({}_{2}\) catalyst [46].  
Ketoprofen irradiation already achieved a high level of drug degradation after 5 min; a high level of drug degradation was achieved, and after 15 min, the signal from this analyte was below the limit of detection (0.5 mg/L), and the two new peaks appeared on the chromatogram (Figure 1a). During further irradiation, the signal of the one decomposition product decreased, and a high signal in the injection peak after 60 min was observed. It suggests that this compound was further degraded. [PERSON] et al. reported that ketoprofen has a higher photoliability to absorb monochromatic light at \(\lambda\) = 254 nm than diclofenac [47]. They compared the photodegradation kinetics of these two compounds in clean water and wastewater. The time-based degradation rate constants for UV photolysis of ketoprofen and diclofenac in clean water were 0.018 s\({}^{-1}\) and 0.042 s\({}^{-1}\), respectively. For filtered and unfiltered wastewaters, these values for ketoprofen were 0.009 s\({}^{-1}\) and 0.018 s\({}^{-1}\), and for diclofenac were 0.016 s\({}^{-1}\) and 0.008 s\({}^{-1}\), respectively. The higher photodegradation of ketoprofen in unfiltered than in filtered wastewater may suggest increasing indirect photolysis from free radicals arising from particulate organic matter. Additionally, the formation of new chromatographic peaks (3 peaks were identified from ketoprofen photolysis and six peaks from diclofenac) corresponds to transformation products [47].  
Chromotograms obtained after UV irradiation of naproxen and diclofenac solutions are shown in Figure 1b,c. The 20% decrease in the signal intensity for diclofenac was observed after just 5 min of irradiation, and two additional peaks appeared on the chromatogram. After 30 min, more than half of the drug was degraded, and after an hour of the process, more than 70% of the analyte was degraded (Figure 1b). For naproxen, a decrease in signal intensity was also observed after 5 min of irradiation, and after 15 min, about 45% of the drug was degraded. Decomposition of the analyte with an efficiency of ~90% was recordedafter 60 min of the process. After 15 min of naproxen irradiation, two new signals were observed; the intensity of one of them decreased over time (Figure 1c).  
Figure 1d shows the relation between signal change and time of photolysis for all analytes. As a result of photolytic processes, the complete decomposition of ketoprofen was achieved after 15 min. High degradation yields were also obtained for naproxen and diclofenac, where after 60 min of the process, 70% (for DFC) and 90% (for NPX) were degraded. Both paracetamol and ibuprofen did not decompose under the used conditions.