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Article

Photocatalytic Degradation of Selected Non-Opioid Analgesics Driven by Solar Light Exposure

by
Ewa Pobozy
*,
Sylwia Kaczmarek
,
Krzysztof Miecznikowski
,
Krystyna Pyrzynska
and
Magdalena Biesaga
*
Faculty of Chemistry, University of Warsaw, Pasteur Str. 1, 02-093 Warsaw, Poland
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2024, 14(17), 7768; https://doi.org/10.3390/app14177768
Submission received: 14 July 2024 / Revised: 24 August 2024 / Accepted: 30 August 2024 / Published: 3 September 2024
(This article belongs to the Section Chemical and Molecular Sciences)
Browse Figures
Versions Notes

Abstract

:
The residues of pharmaceutical compounds are often resistant to degradation, causing an environmental problem. Our research aimed to perform a study of the photocatalytic and photoelectrocatalytic degradation of non-opioid analgesic paracetamol and some of the non-steroidal anti-inflammatory drugs (NSAIDs) (ketoprofen, naproxen, diclofenac, and ibuprofen). Semiconductor WO3, Fe2O3, and WO3/Fe2O3 photocatalysis using solar energy lamps were applied for this purpose. As a result of the photocatalytic processes, high decomposition efficiency was obtained for ketoprofen (97%) and naproxen (70%). Low photodegradation yields were achieved for diclofenac. Under the used measurement conditions, both paracetamol and ibuprofen were not degraded.

1. Introduction

Aquatic pollution caused by a great number of pharmaceutical compounds is an environmental problem that has become an important public health issue over the last years [1,2]. Several laboratory studies have sought to identify the hazards and assess risks in the aquatic environment, and field studies have searched for targeted candidates and occurrence trends. The residues of pharmaceutical compounds are frequently detected in different environmental compartments (drinking water sources, water and sewage treatment plants, and aqua-fauna) due to their universal consumption, low human metabolic capability, and improper disposal [3,4]. Many of these compounds are resistant to degradation and may remain in the environment over a long time, with the potential to cause adverse effects [5,6]. Additionally, the excreted metabolites may become secondary pollutants and can be further modified in receiving waters.
Various approaches have been conducted for the removal and degradation of pharmaceutical residues, such as membrane filtration [7], activated carbon adsorption [8,9], bioremediation [10], and advanced oxidation processes (AOP) [11,12,13,14]. AOP methods involve the in situ generation of hydroxyl radicals and include treatments such as ozonation, Fenton oxidation, and heterogeneous photocatalysis. Among them, semiconductor photocatalysis, based on the concept of achieving the degradation of pollutants by solar energy/UV lamps in the presence of a semiconductor photocatalyst, allows rapid transformation of the initial compound into harmless products. The mechanism of the phenomenon was well described by Khan et al. [15]. This reagent-free methodology requires only a source of radiation (UV or sunlight) and a photocatalyst, and compared with other methods, the photocatalysts can be regenerated and recycled without the need for pretreatment.
The used photocatalysts should offer the required combination of the properties (activity, selectivity, lifetime, and toxicity) and also be cost-effective [16]. Several semiconductors have been studied in photocatalytic oxidations, such as TiO2, Fe3O4, WO3, Fe2O3, and ZnO, as well as the mixtures of these oxides. Among them, titanium oxide is the most widely applied due to its high oxidation efficiency, non-toxicity, high photostability over a broad pH range, chemical inertness, and low cost [17]. However, despite these advantages, TiO2 suffers from low photocatalytic efficiency under visible-light irradiation (only 3–5%) and a narrow light response range because of its intrinsic large band gap of 3.2 eV, which restricts its use under visible light. Therefore, solar systems that use only pure TiO2 have limited efficiency in the degradation of pollutants. Several attempts have been proposed to reduce the band gap energy of TiO2 and to shift its adsorption to visible light. Moreover, due to the surface limitation of TiO2 and its non-porous structure, the studies are directed towards photocatalyst incorporation on porous support to obtain efficient absorption of target pollutants before their subsequent oxidation. Various noble and transition metals, carbon-derived nanoparticles, and minerals are doped with TiO2 to enhance their photodegradation performance [12,18,19,20]. In addition, a hybrid photocatalytic system integrating with membrane filtration has been proposed [11,21,22,23]. The photocatalyst can be suspended in a sample solution or immobilized in/on a membrane [22]. The immobilized system could avoid catalyst aggregation and tedious recycling processes performing high-efficiency removal [22]. Photocatalytic membrane reactors have been applied in water and wastewater treatment to remove pharmaceutical residuals and personal care products.
Doped TiO2 photocatalysts were used for the degradation of some analgesics. With the presence of TiO2/KAl(SO4)2, 95% removal of 0.10 mM acetaminophen in 540 min irradiation time was achieved [24]. The optimal conditions were obtained at pH 6.9 with a dose of 1.0 g/L of photocatalyst at 30 °C. A kinetic study showed that photocatalytic degradation of acetaminophen fits well in the pseudo-first-order model. Competitive reactions from intermediates affected its degradation rate and were more obvious as the initial drug concentration increased. C-modified titanium oxide using lignin as a carbon precursor has been proposed for the solar photocatalytic degradation of acetaminophen, and complete conversion was achieved after only 1 h under solar irradiation [25]. It should be mentioned that the 99% efficiency of this compound’s photodegradation at 20 mg/L concentration level was reported in the presence of TiO2 catalysts with a nanotubular morphology after 100 min ultraviolet radiation [26]. Efficient photocatalytic degradation of ibuprofen under visible light irradiation was obtained using silver and cerium-co-doped mesoporous TiO2 [27]. The photodegradation reaction of ibuprofen catalyzed by TiO2 immobilized on an active glass surface achieved 85% compound disappearance after 24 h of simulated solar light irradiation [28]. The degradation reaction was fast during the first 20 min, and then it gradually decreased.
The main goal of this study was to investigate the photocatalytic degradation of some non-opioid analgesics that encompass paracetamol (acetaminophen) and the non-steroidal anti-inflammatory drugs (NSAIDs) (ketoprofen, naproxen, diclofenac, ibuprofen), which have been used worldwide among patients. The degradation process of these compounds was conducted under UV/solar light irradiation using nanostructured semiconducting metal oxides such as WO3 and Fe2O3 as well as their composite. These photocatalysts have not been evaluated so far for the degradation of the studied drugs. Nanostructured WO3 showed a photocatalytic effect for lidocaine, a prevalent anesthetic drug, under visible and sunlight with high efficiency (96–98%) within 1 h [29]. Nguyen et al. found that the degradation efficiency of antibiotic amoxicillin by simulated solar irradiation with WO3 decreased with increasing initial drug concentration and pH and increased with increasing catalyst dosage [30]. Biaduń et al. applied the nanostructured WO3/Fe2O3 hybrid system for the photodegradation of some surfactants in water samples [31] as well as for organic matrix decomposition before arsenic [32] and thallium [33] speciation analysis. In the literature, there are also examples of utilizing WO3/Fe2O3 systems in the photodegradation of some dyes [34,35].

2. Materials and Methods

Paracetamol (PAR), diclofenac (DFC), ibuprofen (IBU), ketoprofen (KET), and naproxen (NAX), were purchased from Sigma Aldrich. Methanol was obtained from Merck (Darmstadt, Germany) and formic acid from Sigma-Aldrich. All solvents were HPLC-grade. Water was purified by a Milli-Q system (Millipore).
Individual stock solutions (1 mg/mL) of these compounds were prepared separately using methanol–water (50/50, v/v) as a solvent. All the stock solutions were stored at 4 °C. The standard solutions were obtained by appropriate dilution of stock solutions with ultrapure water before analysis.
Chromatographic measurements were carried out using an Azura Analytical HPLC system (Knauer, Germany) equipped with an AZURA P 6.1L gradient pump and an AZURA 2.1L diode array detector (190–700 nm). The wavelengths 200 nm and 230 nm for naproxen, optimal for UV detection, were chosen. The determination of drugs was accomplished with an X-Bridge Shield C18 (4.6 × 100 mm; 3.5 µm) column. The flow rate was set to 1 mL/min, and the injection volume was 10 μL. Measurements were carried out in isocratic elution, optimized for each analyte.
All analytes exhibit weak acidic properties. Paracetamol with a pKa of 9.38 is neutral over a wide pH range; however, in the case of NSAIDs (pKa = 4–5), a low pH of the mobile phase was required. For paracetamol, 10 mM formic acid at pH 2.8 and MeOH in a ratio of 80:20 v/v; for ketoprofen and naproxen, formic acid at pH 2.8 and MeOH (30:70 v/v); and for diclofenac, ibuprofen formic acid at pH 2.8 and MeOH (20:80 v/v) were used. Photodegradation of pharmaceuticals was controlled for model solutions of a single drug with a concentration of 10 μg/mL (for ibuprofen 20 μg/mL) to observe the degradation products. The ClarityChrom chromatography software analyzed the data obtained.
In the UV photolysis processes, a UV lamp, Hönle VG UVAHAND, emitting radiation with a wavelength of 254 nm and a light intensity of 250 mW/cm2, was used. In the photolysis processes, an Oriel 150 W solar simulator equipped with an AM 1.5 G filter was utilized, which was a photoelectrode-light source space that provided an irradiation intensity on the surface photoelectrode of 100 mW/cm2 (determined by a light meter).

2.1. Preparation of the Photocatalysts

The photocatalysts made of tungsten and iron (hematite) oxides were prepared based on a sol–gel method described in our previous works [36]. Briefly, it was achieved through alternate consecutive deposition of a precursor solution (freshly prepared tungstic acid) and a suspension containing commercially available hematite nanoparticles decorated with borododecatungstic acid (BW12) on the FTO (fluorine-doped tin oxide) conductive glass plate (rectangular surface 1.5 × 4 cm). Tungstic acid was prepared by eluting a 0.5 mol/dm3 Na2WO4 solution through a proton exchange column and collated in ethanol and PEG300 (organic structure-directing agent). A suspension of hematite nanoparticles (Fe2O3) stabilized with BW12 was prepared as follows: a known amount of hematite was dispersed in a 0.5 mol/dm3 borontungstic acid solution using an ultrasonic bath for 15 min. In the nanocomposite WO3/Fe2O3 catalyst, the inner layer was tungsten oxide, the surface of which was covered with a monolayer of Fe2O3. Each layer was annealed separately in an oven at 450 °C for 30 min with an oxygen flow. As the crystallographic structure of semiconductors affects their photocatalytic properties, finally, WO3 in the monoclinic form (the band gap is 2.6 eV) was used [37]. Iron oxide was used in the form of hematite, the band gap width of which is 2.1 eV, which corresponds to the absorption of visible radiation [38,39]. It should be emphasized that the completed structure, physicochemical as well as electrochemical characterization of utilized photocatalytic materials were performed in our previous works [31].

2.2. Irradiation Experiments

UV photodegradation was carried out in a quartz vessel. A total of 10 mL of the standard solution was irradiated (wavelength 254 nm) for 60 min at ambient temperature (22 ± 1 °C). After 5, 15, 30, and 60 min of irradiation, a sample was taken, and the effect was checked by chromatographic analysis.
Photo and photoelectrochemical experiments with WO3 and WO3/Fe2O3 photocatalysts were performed in a typical three-electrode system in the cell known as the “cappuccino cell”, designed by École Polytechnique Fédérale de Lausanne (EPFL), Switzerland [40]. The photocatalytic material was illuminated from the side of the photoactive film/electrolyte interface (window surface 0.28 cm2). The plate with the semiconductor acted as the working electrode. The measurements were carried out with the application of a constant oxidation potential of +1.2 V.
Due to the limited stability of the semiconductive layers, irradiation was carried out in an acidic solution. Aqueous drug solutions were acidified with sulfuric acid (VI). Measurements using WO3 were carried out at pH 2, while for WO3/Fe2O3 at pH 4.
To obtain some information about the mechanism of photocatalytic degradation of NSAIDs and the active species created during these photocatalytic processes, different scavengers were employed. Here, ethylenediaminetetraacetic acid disodium (EDTA-Na), KBrO3, and isopropyl alcohol were utilized as hole (h+), electron (e−), and OH scavengers, respectively [41,42,43,44].

3. Results

3.1. 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 H2O2 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. Trujillano et al. found that paracetamol degradation during UV irradiation was almost entirely due to the photoactivity of the used TiO2 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. Salgado et al. reported that ketoprofen has a higher photoliability to absorb monochromatic light at λ = 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].
Chromatograms 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 recorded after 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.

3.2. Photocatalysis and Photoelectrocatalysis—Systems with Tungsten Oxide and Iron Oxide

WO3 nanomaterial is a promising semiconductor to enhance photocatalytic reaction under solar light irradiation thanks to a band gap energy in the range of 2.7–3.0 eV, large surface area, porous structure, and absorbs radiation in the visible range (λ = 480 nm) [48,49]. It is also very stable in low-pH aqueous solutions. However, its photoactivity is hindered by the rapid recombination of photogenerated electrons and hole recombination. One of the proposed methods for improving the photocatalytic performance of WO3 is the formation of heterojunctions with other semiconducting materials [46,49]. Several papers demonstrated the utilization of photoactive films containing WO3 and Fe2O3 prepared layer-by-layer method [30,31,50].
In this study, the photocatalytic degradation of studied pharmaceuticals using WO3 and Fe2O3 applied individually and in their hybrid system WO3/Fe2O3 under solar irradiation was investigated. Additionally, the evaluation of these photocatalysts was performed by the photoelectrochemical process, a new technology to overcome the limitations of conventional photocatalysis [46,48,49,51]. It combines the strengths of both heterogeneous photocatalysis and anodic oxidation for the effective degradation of organic pollutants. Both experiments were conducted in a special cell.

3.2.1. Application of WO3 and Fe2O3 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 WO3 (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 WO3.
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 (tR = 3.1 min and tR = 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. Cristino et al. reported that ketoprofen was not degraded during a sun irradiation cycle of 5 h using colloidal WO3 thin film [52]. It was explained by the electrostatic repulsion between the negative charge of ketoprofen at pH 6 and the negatively charged WO3 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 WO3 immobilized on the FTO plate (4 × 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 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. After 30 min, another additional signal appeared on the chromatogram, with a retention time of 3.2 min, the surface area of which increased intensively with a further extension of the photocatalysis time. During the process, the intensity of the naproxen peak steadily decreased (Figure S2). In the final stage, 70% of the drug was degraded (Figure 3b). It should be mentioned that in the photolytic tests (without photocatalyst) under the same measurement conditions, a 45% decrease in the content of naproxen was observed. Thus, the decomposition of the analyte in the presence of WO3 proceeds much faster. Comparison of these results with those present in Figure 2 led to the conclusion that an increase in the photocatalyst active surface significantly enhances the efficiency of the decomposition of studied analytes.
The photolytic degradation of diclofenac with Fe2O3 under solar light was conducted in neutral media due to the limited solubility of this compound in an acidic environment. α-Fe2O3 (hematite) has an advantage over the other conventional photocatalysts, like TiO2 or ZnO, of a low band gap (~2.2 eV) and using visible light for its photocatalytic reactions [53]. When the diclofenac solution was irradiated, a new chromatographic peak appeared with a retention time of 3.1 min, similar to that observed during the photolysis process (Figure 1c). However, using a solar lamp assisted with Fe2O3, only about 20% of diclofenac was degraded (by UV, it was ~15%) (Figure S3). It suggests that the observed catalytic effect was minimal.

3.2.2. Application of Hybrid WO3/Fe2O3 Photocatalyst

The efficiency of degradation of studied compounds using hybrid WO3/Fe2O3 either in a photocatalytic or photoelectrocatalytic process, as presented in Figure 4, is very similar to that obtained using WO3 alone. During irradiation by a solar lamp, only the content of ketoprofen was decreased gradually, but still, about 70% of its content remained in the unchanged form after 90 min. Two new peaks appeared at tR = 3.1 and 3.5 min, and the surface area under these peaks increased during prolonged irradiation time (Figure S4). The content of other studied pharmaceuticals did not change significantly. Thus, the application of composite WO3/Fe2O3 in photocatalysis and photoelectrocatalysis processes did not increase the efficiency of their degradation. Due to the difficulties of the degradation of ketoprofen, Pt–TiO2–Nb2O5 heterojunction has been proposed for the photocatalytic removal of ketoprofen under UV light irradiation [54]. It was found that the proposed composite exhibited photodecomposition of ketoprofen with a rate constant of 0.075 min−1, which was higher than those of Pt–TiO2 (0.0597 min−1). According to this study, elemental Pt nanoparticles could act as a bridge between TiO2 and Nb2O5, improving the electron-hole separation.
Photodegradation of drug substances involves complex reaction mechanisms that yield various products throughout the degradation pathways. A representative degradation process involves oxidation–reduction, ring alteration, and polymerization, which can be catalyzed or accelerated in the presence of any form of light. Photodegradation might take place in two ways: photooxidative degradation or photolysis. Photooxidative degradation happens when the drugs react with oxidants, such as hydroxyl radicals, which are formed as a result of photolysis. It occurs when drugs absorb light, which results in a change in the conformation of drugs and, thereby, their degradation. Physicochemical properties of the drugs and wastewater, intensity, and wavelength of light control the process of photodegradation. At the same time, light exposure is essential for photodegradation to occur.

3.3. 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 WO3 with an active surface area of 6 cm2 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 tR = 3.9 and 4.1 min gradually increased up to 60 min and then decreased, but the intensity of the new signal obtained at tR = 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).
Pĕrez-Lucas 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 TiO2 in combination with a strong oxidant (Na2S2O8) [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 •O2. In the opposite, 1 mM KBrO3 was utilized as an electron scavenger, inhibiting the reduction of O2 into O2 radicals participating in degrading ketoprofen. Additionally, isopropyl alcohol (1 mM) was utilized to catch •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 KBrO3 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 (•OH scavenger), the photodegradation efficiency decreased by around 22%, indicating that •OH was also the main species that supported the photodegradation of KET. Based on these outcomes, it can be figured out that •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 KBrO3, 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). The obtained results indicate that a different mechanism of photodegradation occurred.

4. Conclusions

In the photocatalytic processes using the WO3 catalyst and the WO3/Fe2O3 composite system, there were large differences in the degradation rate between the individual studied pharmaceuticals, and ketoprofen and naproxen degraded the fastest. Paracetamol and ibuprofen turned out to be the most persistent compounds. The use of electrochemical support did not significantly affect the degradation efficiency of the studied pharmaceuticals. As a result of Fe2O3 photocatalysis, diclofenac is decomposed with low efficiency.
In recent years, different photocatalysts have been proposed to obtain efficient degradation of pharmaceuticals resistant to degradation [56,57]. Several methods have been introduced to improve their photocatalytic activity, such as morphology and crystal modification, doping induction, plasmonic nanoparticle deposition, heterojunction construction with other semiconductor materials, and organic modification [58]. Doping heterogeneous atoms into bismuth oxyhalides was recognized as an effective method to improve the degradation of ibuprofen [59]. The CuS-Fe3O4/reduced graphite oxide catalyst indicated 96% of the removal of ibuprofen under visible light [60].
The semiconductor contact surface area plays an important role in photocatalytic processes. Increasing the active surface area of the photocatalyst significantly increased the efficiency of the decomposition process.
The appearance of signals from some degradation products was observed during irradiation. In further studies, the structures of the possible transformation products will be elucidated using tandem mass spectrometry, as some of the photoproducts obtained may have a higher potential toxicity than the tested drugs themselves.
Our research is now directed towards the fabrication of hybrid photocatalysts based on WO3 junctions with other semiconductors (TiO2, BiVO4, Cu2O), where the greater light harvesting should provide for a considerable enhancement of the photoelectrochemical degradation of drugs.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/app14177768/s1, Figure S1: Chromatograms recorded during irradiation of the tested analytes with WO3 (0.28 cm2 active area) under a solar lamp over time: (A) photocatalysis; (B) photoelectrocatalysis; Figure S2: Chromatograms obtained during photocatalysis of (A) ketoprofen and (B) naproxen with WO3 (4 × 1.5 cm active area) under a solar lamp over time; Figure S3: Photocatalysis of diclofenac with Fe2O3 (4 × 1.5 cm active area) under solar irradiation. (A) Recorded chromatograms over time. (B) The changes in surface area of obtained signals over time. Figure S4: Chromatograms recorded during irradiation of the tested analytes with WO3/Fe2O3 (0.28 cm2 active area) under a solar lamp over time: (A) photocatalysis; (B) photoelectrocatalysis. Figure S5: Chromatograms recorded after 80 min irradiation of KET with isopropanol (1), EDTA (2), and KBrO3 (3). Signal for KET before degradation (4).

Author Contributions

Conceptualization, E.P. and M.B.; methodology, E.P. and K.M.; formal analysis, S.K.; investigation, E.P. and K.P.; resources, E.P. and S.K.; data curation, E.P. and S.K.; writing—original draft preparation, E.P. and K.P.; writing—review and editing, E.P. and K.P.; supervision, M.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Chromatograms obtained during UV irradiation (a) ketoprofen, (b) naproxen, (c) diclofenac, and (d) decomposition of the tested analytes under the influence of UV radiation over time (S—area of signal). A total of 10 mL of the standard solution was irradiated with UV λ = 254 nm for 60 min at 22 °C.
Figure 1. Chromatograms obtained during UV irradiation (a) ketoprofen, (b) naproxen, (c) diclofenac, and (d) decomposition of the tested analytes under the influence of UV radiation over time (S—area of signal). A total of 10 mL of the standard solution was irradiated with UV λ = 254 nm for 60 min at 22 °C.
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Figure 2. Decomposition of the tested compounds with WO3 (active area 0.28 cm2) under solar lamp radiation over time: (a) photocatalysis; (b) photoelectrocatalysis (oxidation potential of +1.2 V).
Figure 2. Decomposition of the tested compounds with WO3 (active area 0.28 cm2) under solar lamp radiation over time: (a) photocatalysis; (b) photoelectrocatalysis (oxidation potential of +1.2 V).
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Figure 3. The changes in the surface areas of signals detected during solar lamp radiation with WO3 photocatalyst (active area 4 × 1.5 cm) for (a) ketoprofen and (b) naproxen.
Figure 3. The changes in the surface areas of signals detected during solar lamp radiation with WO3 photocatalyst (active area 4 × 1.5 cm) for (a) ketoprofen and (b) naproxen.
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Figure 4. Decomposition of the tested analytes with WO3/Fe2O3 hybrid photocatalyst (active area 0.28 cm2) under solar lamp radiation over time: (a) photocatalysis; (b) photoelectrocatalysis (oxidation potential of +1.2 V).
Figure 4. Decomposition of the tested analytes with WO3/Fe2O3 hybrid photocatalyst (active area 0.28 cm2) under solar lamp radiation over time: (a) photocatalysis; (b) photoelectrocatalysis (oxidation potential of +1.2 V).
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Figure 5. Chromatograms obtained during irradiation of ketoprofen in river water matrix with solar lamp and WO3 as photocatalyst (active area 4 × 1.5 cm) (a); decomposition of the ketoprofen over time in ultrapure water and river waters (b). Sample volume: 10 mL, pH 2.
Figure 5. Chromatograms obtained during irradiation of ketoprofen in river water matrix with solar lamp and WO3 as photocatalyst (active area 4 × 1.5 cm) (a); decomposition of the ketoprofen over time in ultrapure water and river waters (b). Sample volume: 10 mL, pH 2.
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Pobozy, E.; Kaczmarek, S.; Miecznikowski, K.; Pyrzynska, K.; Biesaga, M. Photocatalytic Degradation of Selected Non-Opioid Analgesics Driven by Solar Light Exposure. Appl. Sci. 2024, 14, 7768. https://doi.org/10.3390/app14177768

AMA Style

Pobozy E, Kaczmarek S, Miecznikowski K, Pyrzynska K, Biesaga M. Photocatalytic Degradation of Selected Non-Opioid Analgesics Driven by Solar Light Exposure. Applied Sciences. 2024; 14(17):7768. https://doi.org/10.3390/app14177768

Chicago/Turabian Style

Pobozy, Ewa, Sylwia Kaczmarek, Krzysztof Miecznikowski, Krystyna Pyrzynska, and Magdalena Biesaga. 2024. "Photocatalytic Degradation of Selected Non-Opioid Analgesics Driven by Solar Light Exposure" Applied Sciences 14, no. 17: 7768. https://doi.org/10.3390/app14177768

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