Photocatalytic Degradation Of Diclofenac Research Articles

Photocatalytic Degradation of Diclofenac in Tap Water on TiO2 Nanotubes Assisted with Ozone Generated from Boron-Doped Diamond Electrode

Degradation of pharmaceuticals in water by TiO2 photocatalysis often suffers from low efficiency due to low activity and mass transfer limitation. In this work, diclofenac removal in tap water was performed by photocatalysis on TiO2 nanotube growth on Ti mesh substrate assisted by ozone (O3), which was generated from a hole-arrayed boron-doped diamond (HABDD) film electrode. The vertically oriented TiO2 nanotubes were used as the heterogeneous photocatalyst. The HABDD, as a self-standing diamond electrode, was designed and custom-made by MWCVD technology. The microstructures and crystalline of the TiO2 nanotubes and HABDD were characterized by a scanning electronic micrograph (SEM) and X-ray diffraction (XRD). Unlike other ozone generation methods, direct generation of ozone in the flowing water was applied in the photocatalysis process, and its effect was discussed. The diclofenac removal performance of the electrochemical-photocatalytic system was studied depending on O3 generation efficiency, flowing rate, and the initial diclofenac concentration. The enhanced degradation effect from O3 molecules on TiO2 photocatalysis was attributed to the larger active surface area, the increased photo-generated charge separation rate, and the contact area of O3. The degradation efficiency in the combined electrochemical-photocatalytic TiO2/O3/UV system was higher than that of the O3/UV and TiO2/UV routes individually. Furthermore, a theoretical calculation was used to analyze the TiO2/O3 interface in aqueous media in terms of the final energy. This system created an almost in situ feeding channel of oxidants in the TiO2 photocatalysis process, thus increasing photocatalytic efficiency. This synergetic system is promising in the treatment of pharmaceuticals in water.

Photocatalytic degradation of diclofenac using a novel double Z-scheme catalyst (O-g-C3N4/ZnO/TiO2@halloysite nanotubes): Degradation mechanism, identification of by-products and environmental implementation

It is challenging and expensive to synthesize multivariate composites with high photocatalytic efficiency and recyclability. Herein, a novel direct double Z-scheme O-g-C3N4/ZnO/TiO2@halloysite nanotubes (HNTs) photocatalyst was synthesized using a simple and low-cost method to degrade and mineralize diclofenac (DCF). During 50 min, O-g-C3N4/ZnO/TiO2@HNTs degraded DCF completely at pH 6.83, 10 mg/L DCF concentration, and 1.0 g/L catalyst, which was 1.66 and 2.4 times higher than ternary O-g-C3N4/ZnO/TiO2 and O-g-C3N4/HNTs/TiO2. Under the same conditions, 35.12 % of DCF was removed from urban wastewater. A negative effect of anions on the process was observed as follows: CO32− > HPO42− > Cl− > NO3−. Under the same conditions, 39.23 % of total organic carbon (TOC) was removed. Moreover, Mott-Schottky analysis and active species trapping experiments were performed to investigate the photodegradation mechanism systematically. It was observed that O2− played a minor part in the photodegradation process, while hole and OH were the more critical reactive species. Several intermediate compounds formed during the photocatalytic reaction were identified by LC-MS analysis. The results showed that a simple design and synthesis of multi-component complex catalysts presented a new insight into removing emerging pollutants from the aquatic environment and apprehending the enhanced photocatalytic mechanism.

Photocatalytic Degradation of Diclofenac by Nitrogen-Doped Carbon Quantum Dot-Graphitic Carbon Nitride (CNQD)

In this study nitrogen-doped carbon quantum dots/graphitic carbon nitride nanosheet (CNQD) composites with different contents of nitrogen-doped carbon quantum dots (NCQDs; 2, 4, 6, and 8 wt%) were synthesized. The morphological, physicochemical, and photoelectrochemical properties were investigated using complementary methods such as scanning electron microscopy (SEM), powder X-ray diffraction (pXRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), UV/Vis spectroscopy in diffuse reflectance (DRS), photoluminescence (PL), nitrogen physisorption (BET), photocurrent response, and electrochemical impedance spectroscopy (EIS). The photocatalytic activity of the synthesized materials was assessed during diclofenac (DCF) degradation in an aqueous solution under visible light irradiation. As a result, improved photocatalytic efficiency in DCF degradation was observed for all the CNQD composites compared with bulk graphitic carbon nitride (bCN) and nanosheet g-C3N4 (CNS). The fastest DCF degradation was observed for the 6 wt% NCQD on the surface of CNS (CNQD-6), which removed 62% of DCF in 3 h, with an associated k value of 5.41 × 10−3 min−1. The performance test results confirmed the contribution of NCQDs to enhancing photocatalytic activity, leading to an improvement factor of 1.24 over bCN. The morphology of the CNS and the synergistic interaction between NCQDs and CNS were essential elements for enhancing photocatalytic activity. The photoelectrochemical data and photoluminescence analyses showed the efficient migration of photoexcited electrons from NCQDs to the CNS. The reduced charge recombination rates in CNQD photocatalysts might be due to the synergistic interaction between NCQDs and CNS and the unique up-conversion photoluminescence properties of NCQDs. Further investigations revealed that the photogenerated superoxide radicals (•O2−) predominated in the degradation of DCF, and this photocatalyst had good reusability and toxicity reduction abilities. This work provides insight into the effects of NCQDs on the CNS surface to enhance its potential to remove emerging organic pollutants from water and wastewater.

Ultrasonication-assisted synthesis of CN–TiO2 and its photocatalytic degradation of diclofenac under visible light irradiation

ABSTRACT In this study, CN codoped TiO2 nanoparticles (CN–TiO2) were fabricated by solvothermal and low temperature calcination methods with the aid of ultrasonication. According to the number of ultrasonic treatments used in the preparation process, the samples were named NN, YN, NY and YY. The characteristics of transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible spectroscopy (UV–vis) were employed to analyse the effect of the ultrasonic treatment step in the synthetic process. The results showed that ultrasonication can increase the CN content in TiO2, reduce the band gap energy, and improve the catalytic performance of the CN–TiO2, and the effect of secondary ultrasound is particularly obvious. The YY obtained by two-step ultrasonication with the lowest band gap energy of 3.07 eV. The photocatalytic activity of the CN–TiO2 was evaluated using the degradation of diclofenac (DCF) under visible light irradiation (white LED strips with an emission wavelength of 450 nm). It was observed that the YY exhibited significantly superior DCF degradation activity. When using 0.4 g L–1 of YY, an excellent DCF degradation of 97% could be reached, which is 1.4 times that of NN (without ultrasonication). Moreover, YY had good visible light photocatalytic activity, and the degradation efficiency of YY for DCF under visible light was comparable to that of a xenon lamp. Therefore, ultrasonication played a critical role in the enhancement of photocatalytic activity during the synthesis of CN–TiO2.

Fouling control in a submerged membrane reactor: Aeration vs membrane oscillations

• Aeration and membrane oscillation as fouling mitigation strategies were compared. • Membrane oscillation is effective for mitigating membrane fouling due to particle deposition. • Predicted and experimental results matched reasonably well. • Model can predict the operating conditions for particle deposition on submerged membrane. • Membrane oscillation enhanced diclofenac removal by ∼ two times in a SPMR. Membrane fouling potential due to particle deposition in a submerged membrane reactor (SMR) was investigated using aeration and membrane oscillations. A mathematical model describing the particle dynamics and the magnitude of the forces acting on a particle/agglomerate near a membrane surface was developed. The simulation results were verified by conducting experiments with inert glass bead sizes (2.5–33.0 μm) at various aeration rates (1.0–4.0 LPM), oscillation intensity (frequency 0–11.34 Hz; amplitude 2–6 mm). Additionally, photocatalytic degradation of diclofenac (DCF) (initial concentration = 4 mg/L) using UV 365 nm and TiO 2 photocatalyst was used to characterize the system performance. The results indicate that membrane oscillation was significantly superior as a fouling mitigation strategy due to higher shear rates (up to 10 times) than that of aeration. In the studied operating parameter range, the simulation results indicate that in case of aeration, particles below ∼ 10 µm will be deposited on the membrane. Whereas, in case of membrane oscillation, a much smaller size of 0.1 µm below which particles will be deposited on membrane surface. This was further confirmed by the photocatalytic degradation of DCF using oscillatory membrane in a submerged photocatalytic membrane reactor (SPMR) where close to two times higher DCF degradation occurred using membrane oscillation with a negligible transmembrane pressure drop (TMP) of (0.1–3 kPA). The presented approach will be useful in predicting the membrane fouling due to deposition of polydisperse particles in submerged oscillatory membrane reactors.

Perylene Diimide Growth on Both Sides of Carbon Nanotubes for Remarkably Boosted Photocatalytic Degradation of Diclofenac

Perylene Diimide Growth on Both Sides of Carbon Nanotubes for Remarkably Boosted Photocatalytic Degradation of Diclofenac

Photocatalytic-persulfate- oxidation for diclofenac removal from aqueous solutions: Modeling, optimization and biotoxicity test assessment

In this paper, the influence of several aquatic factors (the nature of catalyst, the initial pH and the initial concentration of the pollutant) on the photocatalytic degradation of diclofenac (DFC), one of the most widely prescribed anti-inflammatory non-steroidal drug, was studied. Also, in order to examine the intensification process, the variation of the photocatalytic DFC degradation in the presence of sodium persulfate (PPS) was analyzed. It was found that, compared to titanium dioxide (TiO2), the zinc oxide (ZnO) photocatalyst performed exceptionally well, with a 96.13% DFC degradation efficiency after 150 min. The photodegradation of DFC by ZnO catalyst fitted well the Langmuir–Hinshelwood kinetic model. The maximum efficiency is 97.27% for simulated solar-UVA/ZnO/PPS and 77% for simulated solar-UVA/ZnO. In order to determine the optimal conditions leading to the maximization of DFC removal, an artificial neural network (ANN) modeling approach combined with genetic algorithm (GA) was applied. The best ANN determined had a correlation of 0.999 and it was further used in the process optimization where a 99.7% degradation efficiency was identified as the optimum under the following conditions: DFC initial concentration 37,9 mg L−1, pH 5,88 and PPS initial concentration 500 mg L−1. The effectiveness of the process and the toxicity of the pharmaceutical pollutants and their by-products were also evaluated and confirmed by the biological tests using liver and kidney of Mus musculus mice.

Removal of Diclofenac in Effluent of Sewage Treatment Plant by Photocatalytic Oxidation

Diclofenac (DCF) has been widely found in sewage treatment plants and environmental water bodies, and has attracted worldwide attention. In this paper, the photocatalytic degradation of DCF was investigated using a laboratory-scale simulated solar experimental device. This study focused on exploring the effects of the actual secondary effluent from sewage treatment plants (SE-A and SE-B) on the photocatalytic degradation of DCF and the changes of dissolved organic matter (DOM) during the photocatalytic degradation process. The results showed when SE-A and SE-B were used as the background water of the DCF solution, they displayed a significant inhibitory effect on the degradation of DCF, and the values of k were 0.039 and 0.0113 min−1, respectively. Among them, DOM played a major inhibitory role in photocatalytic degradation of DCF in sewage. In the photocatalytic process, the biological toxicity of the DCF solution was the least after 30 min of reaction, and then gradually increased. Furthermore, the organic matters in the sewage were greatly degraded after the photocatalytic reaction, including 254 and 365 nm ultraviolet (UV254, UV365) and chemical oxygen demand (COD). Moreover, titanium dioxide (TiO2) first catalyzed the degradation of macromolecular organic matters, and then degraded the small molecular organic matters.

Photocatalytic Degradation of Diclofenac Using Al2O3-Nd2O3 Binary Oxides Prepared by the Sol-Gel Method.

This paper reports the sol-gel synthesis of Al2O3-Nd2O3 (Al-Nd-x; x = 5%, 10%, 15% and 25% of Nd2O3) binary oxides and the photodegradation of diclofenac activated by UV light. Al-Nd-based catalysts were analyzed by N2 physisorption, XRD, TEM, SEM, UV-Vis and PL spectroscopies. The inclusion of Nd2O3 in the aluminum oxide matrix in the 10–25% range reduced the band gap energies from 3.35 eV for the γ-Al2O3 to values as low as 3.13–3.20 eV, which are typical of semiconductor materials absorbing in the UV region. γ-Al2O3 and Al-Nd-x binary oxides reached more than 92.0% of photoconverted diclofenac after 40 min of reaction. However, the photocatalytic activity in the diclofenac degradation using Al-Nd-x with Nd2O3 contents in the range 10–25% was improved with respect to that of γ-Al2O3 at short reaction times. The diclofenac photoconversion using γ-Al2O3 was 63.0% at 10 min of UV light exposure, whereas Al-Nd-15 binary oxide reached 82.0% at this reaction time. The rate constants determined from the kinetic experiments revealed that the highest activities in the aqueous medium were reached with the catalysts with 15% and 25% of Nd2O3, and these compounds presented the lowest band gap energies. The experimental results also demonstrated that Nd2O3 acts as a separator of charges favoring the decrease in the recombination rate of electron-hole pairs.

Effect of dissolved organic matters and inorganic ions on TiO2 photocatalysis of diclofenac: mechanistic study and degradation pathways.

Diclofenac (DCF) exists extensively in sewage treatment plant effluent, and it is one of the most reported environmental pharmaceutical contaminants. In this work, the photocatalytic degradation of DCF by titanium dioxide (TiO2) in pure water under visible light and the influence of humic acids (HA) (as a kind of dissolved organic matter (DOM), phosphate and ferrous ion (Fe2+)) were investigated. The results showed that the lower the pH was, the better the degradation effect of DCF under acidic conditions was. Different concentrations of DOM, phosphate ion, and Fe2+ could inhibit the degradation of DCF, and the higher the concentration was, the stronger the inhibition was. Different concentrations of chloride ions had little effect on the degradation. A slight elimination (8-12.9%) of total organic carbon (TOC) was observed during the mineralization of DCF with and without DOM and inorganic ions, indicating poor mineralization during the process of photocatalytic degradation, and DOM, phosphate, and Fe2+ had little effect on DCF mineralization. Furthermore, hydroxyl radicals, superoxide radicals, and singlet oxygen radicals were present during the photocatalytic degradation of DCF. DOM and inorganic ions could inhibit the intensity of hydroxyl radical and promote superoxide radicals (O2-) and singlet oxygen (1O2) to varying degrees. Finally, the degradation mechanism and main products were analyzed by liquid chromatography-mass spectrometry (LC-MS), and nine possible intermediates were detected. Hydroxylation, dechlorination, cyclization, and oxidation were the main degradation mechanisms. However, DOM, phosphate, and Fe2+ did not affect the type of intermediate products in terms of the mass-to-charge ratio. This paper mainly studied the mechanisms of different influencing factors in simulated environments to provide a theoretical basis for the degradation of DCF in wastewater treatment plants. Graphical abstract.

Synthesis of a core-shell heterostructured MoS2/Cd0.9Zn0.1S photocatalyst for the degradation of diclofenac under visible light

The development of novel noble metal-free semiconductor catalysts with high photocatalytic efficiency is of great importance toward the degradation of organic compounds. In this work, a core-shell heterojunction MoS2/Cd0.9Zn0.1S photocatalytic material was successfully synthesized via a simple one-step hydrothermal method. The introduction of MoS2 led to a significant improvement in the photocatalytic degradation of diclofenac (DCF). It was confirmed that 0.1% loading content of MoS2 achieved an optimal photocatalytic efficiency of 86% in the degradation of DCF under visible light irradiation, which was 1.8 times higher than that of Cd0.9Zn0.1S. The MoS2/Cd0.9Zn0.1S heterostructured composites possessed improved photocatalytic properties, which implied that the combination of Cd0.9Zn0.1S and MoS2 shortened the carrier transport pathway and facilitated the separation efficiency of electrons and holes. Reactive species (RS) scavenging experiments and electron spin resonance (ESR) demonstrated that superoxide radicals (O2•−) and electron holes (h+) played predominant roles throughout the DCF degradation process. The primary intermediates were explored through HRAM LC/MS/MS, and a transformation pathway was tentatively proposed. This study promoted the application of an economical, highly efficient and visible light driven MoS2 co-catalyst for the degradation of organic contaminants.

Visible-light-driven photocatalytic degradation of diclofenac by carbon quantum dots modified porous g-C3N4: Mechanisms, degradation pathway and DFT calculation

Metal-free photocatalysts have attracted growing concern in recent years. In this work, a new class of carbon quantum dots (CQDs) modified porous graphitic carbon nitride (g-C3N4) is synthesized via a facile polymerization method. With the optimal CQDs loading, the CQDs modified g-C3N4 exhibits ∼15 times higher degradation kinetic towards diclofenac (DCF) than that of pure g-C3N4. The enhanced photocatalytic activity can be ascribed to the improved separation of charge carriers as well as the tuned band structure. Moreover, a photosensitation-like mechanism is proposed to elucidate the photo-generated electrons transfer and reactive radicals formation. CQDs are anchored to g-C3N4 surface via C–O bond, which provide channels for the preferential transfer of photo-excited electrons on DCF molecule to the conduction band of g-C3N4. Superoxide radical (·O2−) dominates the degradation of DCF, while holes (h+) show a negligible contribution. Density functional theory (DFT) calculation successfully predicts that the sites on DCF molecule with high Fukui index (f0) are preferable to be attacked by radicals. DCF degradation pathway mainly includes ring hydroxylation, ring closure and C–N bond cleavage processes. Acute toxicity estimation indicates the formation of less toxic intermediates/products compared to DCF after photocatalysis. Moreover, the hybrid photocatalysts exhibit good reusability in five consecutive cycles. This work not only proposes a deep insight into photosensitation-like mechanism in the photocatalysis system by using C3N4-based materials, but also develops new photocatalysts for potential application on removal of emerging organic pollutants from waters and wastewaters.

WITHDRAWN: Visible-light-driven photocatalytic degradation of diclofenac by carbon quantum dots modified porous g-C3N4: Mechanisms, degradation pathway and DFT calculation

Metal-free photocatalysts have attracted growing concern in recent years. In this work, a new class of carbon quantum dots (CQDs) modified porous graphitic carbon nitride (g-C3N4) is synthesized via a facile polymerization method. With the optimal CQDs loading, the CQDs modified g-C3N4 exhibits ∼15 times higher degradation kinetic towards diclofenac (DCF) than that of pure g-C3N4. The enhanced photocatalytic activity can be ascribed to the improved separation of charge carriers as well as the tuned band structure. Moreover, a photosensitation-like mechanism is proposed to elucidate the photo-generated electrons transfer and reactive radicals formation. CQDs are anchored to g-C3N4 surface via CO bond, which provide channels for the preferential transfer of photo-excited electrons on DCF molecule to the conduction band of g-C3N4. Superoxide radical (·O2-) dominates the degradation of DCF, while holes (h+) show a negligible contribution. Density functional theory (DFT) calculation successfully predicts that the sites on DCF molecule with high Fukui index (f0) are preferable to be attacked by radicals. DCF degradation pathway mainly includes ring hydroxylation, ring closure and CN bond cleavage processes. Acute toxicity estimation indicates the formation of less toxic intermediates/products compared to DCF after photocatalysis. Moreover, the hybrid photocatalysts exhibit good reusability in five consecutive cycles. This work not only proposes a deep insight into photosensitation-like mechanism in the photocatalysis system by using C3N4-based materials, but also develops new photocatalysts for potential application on removal of emerging organic pollutants from waters and wastewaters.

Photocatalytic Degradation of Diclofenac by Hydroxyapatite⁻TiO₂ Composite Material: Identification of Transformation Products and Assessment of Toxicity.

Diclofenac (DCF) is one of the most detected pharmaceuticals in environmental water matrices and is known to be recalcitrant to conventional wastewater treatment plants. In this study, degradation of DCF was performed in water by photolysis and photocatalysis using a new synthetized photocatalyst based on hydroxyapatite and TiO2 (HApTi). A degradation of 95% of the target compound was achieved in 24 h by a photocatalytic treatment employing the HApTi catalyst in comparison to only 60% removal by the photolytic process. The investigation of photo-transformation products was performed by means of UPLC-QTOF/MS/MS, and for 14 detected compounds in samples collected during treatment with HApTi, the chemical structure was proposed. The determination of transformation product (TP) toxicity was performed by using different assays: Daphnia magna acute toxicity test, Toxi-ChromoTest, and Lactuca sativa and Solanum lycopersicum germination inhibition test. Overall, the toxicity of the samples obtained from the photocatalytic experiment with HApTi decreased at the end of the treatment, showing the potential applicability of the catalyst for the removal of diclofenac and the detoxification of water matrices.

Construction of novel Z-scheme nitrogen-doped carbon dots/{0 0 1} TiO2 nanosheet photocatalysts for broad-spectrum-driven diclofenac degradation: Mechanism insight, products and effects of natural water matrices

The development of broad spectrum UV–visible-near-infrared (NIR) photocatalysts is a primary strategy in the area of photocatalytically mediated pollutant elimination. Herein, we report on a novel broad-spectrum N-doped carbon quantum dot/TiO2 nanosheet with higher surface energy {0 0 1} faceted (NCDS/TNS-001) composites with significantly improved broad-spectrum utilization. Under UV, visible, and near infrared light irradiation, NCDS/TNS-001 exhibited higher photocatalytic activity than those of TNS-001, NCDs/P25, and NCDs/TiO2 with {1 0 1} facets (NCDs/T-101) toward the degradation of diclofenac (DCF). This excellent photocatalytic performance might be attributed to the synergistic effects of the highly active {0 0 1} facets, up-converted fluorescent properties of NCDs, and efficient charge separation induced by fabricated heterostructures. The determination of reactive species revealed that O2− was the dominant species during the photocatalytic degradation of DCF. Together with the analysis of the band structure, a potential Z-scheme heterojunction mechanism for NCDs/TNS-001 was deduced. Photocatalytic pathways of the DCF were further proposed based on intermediate identification and TOC detection, which involved decarboxylation, hydroxylation, and ring opening reactions. The sufficient degradation of DCF in natural water matrices indicated that using NCDS/TNS-001 photocatalytic process for the treatment of ambient DCF wastewater is technical possible.

Reaction Kinetics and Mechanism of Visible Light Induced Photocatalytic Degradation of Pharmaceutical Drug, Diclofenac in Synthesized N-Doped Tio2 Suspension

The present study deals with investigations on reaction efficiency and mechanism of visible light induced N- doped TiO2 mediated photocatalytic degradation of pharmaceutical drug, diclofenac. The photocatalytic efficiency of the NT-450 for degradation of diclofenac was found to be 90.2% upon irradiation with white light for 120 min, by maintaining the pH of solution at 2 and the observed rate constant for the reaction is found to be 0.0140 min-1. The reaction mechanism of photocatalytic degradation of diclofenac was proposed on the basis of monitoring the temporal evolution of intermediates during the process and their identification by using analytical techniques viz. UV-Vis Spectrometry and Gas Chromatography–Mass Spectrometry (GC/MS). Ten intermediates were identified by GC/MS and plausible pathway for photocatalytic degradation was evolved. The photocatalytic oxidation process is initiated by the generation of hydroxyl free radical and further proceeded by the hydroxylation leading to hydroxylated products, cyclization, cleavage of C-N bond and ring opening. The detailed reaction mechanism for the degradation process has been established.

Efficacy of the Reactive Oxygen Species Generated by Immobilized TiO2in the Photocatalytic Degradation of Diclofenac

We report on the photodegradation of diclofenac (DCF) by hydrothermal anatase nanocrystals either free or immobilized in porous silica matrix (TS) in connection to the type and amount of reactive oxygen species (ROS), in order to have deeper insight into their role in the photocatalysis and to provide an effective tool to implement the DCF mineralization. TiO2and TS exhibit a remarkable efficiency in the DCF abatement, supporting that the utilization of anatase nanoparticles with the highly reactive{001},{010}, and{101}exposed surfaces can be an effective way for enhancing the photooxidation even of the persistent pollutants. Furthermore, the hydrothermal TiO2, when immobilized in silica matrix, preserves its functional properties, combining high photoactivity with an easy technical use and recovery of the catalyst. The catalysts performances have been related to the presence of OH•,O21, andO2-•species by electron paramagnetic resonance spin-trap technique. The results demonstrated that the ROS concentration increases with the increase of photoactivity and indicated a significant involvement ofO21in the DCF degradation. The efficacy of TiO2when immobilized on a silica matrix was associated with the high ROS life time and with the presence of singlet oxygen, which contributes to the complete photomineralization of DCF.

Aqueous degradation of diclofenac by heterogeneous photocatalysis using nanostructured materials

The photocatalytic degradation of diclofenac (DIC), 2-[2′, 6′-(dichlorophenyl)amino]phenylacetic acid is investigated under near UV–Vis and UV irradiation, using commercial TiO2 P25, synthesized TiO2 (anatase and rutile) and functionalized multi-walled carbon nanotube (MWCNTox): anatase (10-MWCNTox–TiO2) suspensions as catalysts. Factors affecting the kinetics of the process, such as the type and load of photocatalyst, and the presence of dissolved O2, or addition of H2O2 as co-oxidant have been compared. The degradation under UV irradiation is more effective than under near UV–Vis. Optimal conditions for a complete removal were obtained using synthesized anatase (0.5gL−1) and 50% O2 (v/v) under UV irradiation, with rate constants ca. 0.9min−1 (half-life time ca. 0.8min). Eight photoproducts were observed from DIC photodegradation, mainly corresponding to photocyclisation (2-(8-chloro-9H-carbazol-1-yl)acetic acid, 1-chloro-8-methyl-9H-carbazole), decarboxylation (2,6-dichloro-N-o-tolylbenzenamine) and dehalogenation.

LC-MS for identifying photodegradation products of pharmaceuticals in the environment

Abiotic processes, such as direct and indirect photolysis, are of great importance in determining the aquatic fate of pharmaceutical compounds. Photolytic reactions are often complex, involving various competing or parallel pathways and leading to multiple reaction products. The identification of transformation products and the elucidation of photolysis-reaction pathways are of crucial importance in understanding their fate in the aquatic environment, but are complicated and cumbersome. This article focuses on advanced liquid chromatography-mass spectrometry (LC-MS) methods for identifying transformation products of abiotic processes that lead to the transformation of pharmaceutical compounds in environmental systems (direct and indirect photolysis) and photocatalytic transformations in water- and wastewater-treatment systems, using titanium dioxide or the photo-Fenton process. We discuss the capabilities and the limitations of single-MS, tandem-MS and hybrid-MS techniques, and present practical examples (triple-quadrupole-MS analysis of phototransformation products of fluoxetine, ion-trap-MS analysis of photoproducts of carbamazepine, and time-of-flight-MS elucidation of the reaction pathways of photolytic and photocatalytic degradation of diclofenac).