Photochemical Degradation Research Articles

Temperature Dependence of Photochemical Degradation of MAPbBr3 Perovskite

The experimental results of X-ray diffraction (XRD), optical absorbance, scanning electron microscopy (SEM), and X-ray photoelectron spectra (XPS) of the core levels and valence bands of MAPbBr3 (MA-CH3NH3+) perovskite before and after exposure to visible light for 700 h at temperatures of 10 and 60 °C are presented. It reveals that the light soaking at 60 °C induces the decomposition of MAPbBr3 perovskite accompanied with the decay of organic cation and the release of a PbBr2 phase as a degradation product whereas the photochemical degradation completely disappears while the aging temperature is decreased to 10 °C.

Role of light in methylmercury photodegradation: From irradiation to absorption in the presence of organic ligands

Photochemical degradation acts as the principal sink for methylmercury (MeHg) in surface water, which is regulated by light and solution matrix (especially the presence of dissolved organic matter, DOM). The spectral composition of light irradiation and the light absorption properties of reaction media (often exerted by DOM) are important in MeHg photodegradation, which has not yet been clearly resolved. Aiming to understand the role of light in MeHg photodegradation from the perspectives of both light irradiation and absorption, we investigated the photodegradation of MeHg under different simulated sunlight sources, with and without DOM model compounds of different molecular structures. The results show that the photodegradation of MeHg under different sunlight irradiation yields distinct first-order date constant, mainly due to the slight difference in UVB composition. The degradation of MeHg without DOM under a light source with high intensity in the UV region and no MeHg degradation under the UV-filtered light even in the presence of DOM showed the importance of UV lights in MeHg photodegradation. The use of ultrapure water as a reaction medium may be subject to MeHg loss through vessel adsorption, not just photolysis. Additionally, this work found that the type and position of coexisting substituents on aromatic thiols play a critical role in improving the photodegradation of MeHg, following amino > hydroxyl > carboxyl, para > meta > ortho. Based on the characterization of ultraviolet-visible absorption spectra and our previous work, it was concluded that the presence of DOM could induce red-shift in light absorption and reduce the electronic transition energy of the CHg bond, facilitating MeHg photodegradation. The structures of DOM affect the light absorption properties, which are related to MeHg photodegradation.

Synthesizing Laboratory and Field Experiments to Quantify Dominant Transformation Mechanisms of 2,4-Dichlorophenoxyacetic Acid (2,4-D) in Aquatic Environments.

Laboratory studies used to assess the environmental fate of organic chemicals such as pesticides fail to replicate environmental conditions, resulting in large errors in predicted transformation rates. We combine laboratory and field data to identify the dominant loss processes of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in lakes for the first time. Microbial and photochemical degradation are individually assessed using laboratory-based microcosms and irradiation studies, respectively. Field campaigns are conducted in six lakes to quantify 2,4-D loss following large-scale herbicide treatments. Irradiation studies show that 2,4-D undergoes direct photodegradation, but modeling efforts demonstrated that this process is negligible under environmental conditions. Microcosms constructed using field inocula show that sediment microbial communities are responsible for degradation of 2,4-D in lakes. Attempts to quantify transformation products are unsuccessful in both laboratory and field studies, suggesting that their persistence is not a major concern. The synthesis of laboratory and field experiments is used to demonstrate best practices in designing laboratory persistence studies and in using those results to mechanistically predict contaminant fate in complex aquatic environments.

Real-time air concentrations and turbulent fluxes of volatile organic compounds (VOCs) over historic closed landfills to assess their potential environmental impact

For the first time, emission/deposition fluxes of volatile organic compounds (VOCs) and H2S from a historic closed landfill site in Southern Italy were determined by Eddy Covariance (EC) using Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-TOF-MS). This was done in two field campaigns of one week performed in July and October 2016, where fluxes of CO2 and CH4 were also measured. Many compounds not previously identified in the biogas were detected by PTR-TOF-MS, but only in July some of them produced positive fluxes exceeding the flux limit of detection. Methanol was the most emitted compound with an average flux of 44.20 ± 4.28 μg m−2 h−1, followed by toluene with a mean flux of 18.97 ± 2.47 μg m−2 h−1. Toluene fluxes were 10 times higher than those of benzene, fitting rather well with values previously measured in the biogas. VOCs emission fluxes of monoterpenes and highly reactive arenes did not reflect, however, the biogas composition. This, combined with tiny emissions of VOC oxidation products, suggests that landfill emissions underwent some photochemical degradation before being dispersed in the atmospheric boundary layer (ABL). Deposition fluxes of some VOCs emitted from the sea was also observed in July. No relevant VOC fluxes were instead measured in October, suggesting that temperature was the variable controlling most landfill emission. Albeit small, summer landfill emissions from the investigated site can have an impact on the population living nearby, because they contain or still generate compounds that causing nuisance.

The Preparation of Hydroxyl-Terminated Deproteinized Natural Rubber Latex by Photochemical Reaction Utilizing Nanometric TiO2 Depositing on Quartz Substrate as a Photocatalyst.

Hydroxyl-terminated natural rubber (HTNR) is a product of interest for making natural rubber (NR) easy and versatile for use in a wide range of applications. Photochemical degradation using a TiO2 film that has been deposited on a glass substrate is one of the fascinating methods of producing HTNR. Nevertheless, light energy is wasted during the photodegradation process because a glass substrate has a cutoff for ultraviolet light. To enhance the effectiveness of the process, a quartz substrate was coated with the TiO2 film for photochemical breakdown. X-ray diffraction (XRD) spectroscopy and atomic force microscopy (AFM) were applied to investigate the TiO2 deposited on glass and quartz substrates. In addition, the influence of several factors, such as rubber and surfactant concentrations, on the reaction was investigated. After the reaction, the properties of the rubber products, including intrinsic viscosity, molecular weight, and microstructure, were determined. A unique diffraction peak for the anatase (101) phase could be observed in the TiO2 film deposited on the quartz substrate, resulting in photochemical activity and photocatalytic efficiency significantly higher than those of the substrate made of glass. In the scenario of deproteinized NR (DPNR) latex containing 10% DRC, 20% w/w H2O2, and TiO2 film coated on a quartz substrate, the HTNR could be manufactured effectively.

Photostability and Dynamic Helical Behavior in Chiral Poly(phenylacetylene)s with a Preferred Screw-Sense.

Helical polymers such as poly(phenylacetylene)s (PPAs) are interesting materials due to the possibility of tuning their helical scaffold (sense and elongation) once they have been prepared and by the presence of external stimuli. The main limitation in the application of PPAs is their poor photostability. These polymers degrade under visible light exposure through a photochemical electrocyclization process. In this work, it was demonstrated, through a selected example, how the photochemical degradation in PPAs is directly related to their dynamic helical behavior. Thus, while PPAs with dynamic helical structures show poor photostability under UV/Vis light exposure, poly‐(R)‐1, bearing an enantiopure sulfoxide group as pendant group and designed to have a quasi‐static helical behavior, shows a large photostability due to the restricted conformational composition at the polyene backbone, needed to orient the conjugated double bonds prior to the photochemical electrocyclization process and the subsequent degradation of the material.

Photostability and Dynamic Helical Behavior in Chiral Poly(phenylacetylene)s with a Preferred Screw‐Sense

AbstractHelical polymers such as poly(phenylacetylene)s (PPAs) are interesting materials due to the possibility of tuning their helical scaffold (sense and elongation) once they have been prepared and by the presence of external stimuli. The main limitation in the application of PPAs is their poor photostability. These polymers degrade under visible light exposure through a photochemical electrocyclization process. In this work, it was demonstrated, through a selected example, how the photochemical degradation in PPAs is directly related to their dynamic helical behavior. Thus, while PPAs with dynamic helical structures show poor photostability under UV/Vis light exposure, poly‐(R)‐1, bearing an enantiopure sulfoxide group as pendant group and designed to have a quasi‐static helical behavior, shows a large photostability due to the restricted conformational composition at the polyene backbone, needed to orient the conjugated double bonds prior to the photochemical electrocyclization process and the subsequent degradation of the material.

Low Fluorinated Oligoamides for Use as Wood Protective Coating

New highly hydrophobic fluorinated oligoamides were synthesized and studied as materials for the protection of non-varnishable wooden artifacts. The new oligoamides were designed to achieve the best performance (including high chemical affinity to the wood material) and the lowest environmental impact. In order to minimize the risk of bioaccumulation, short perfluoroalkyl side chains were reacted with oligoethylene L-tartaramide (ET), oligoethylene adipamide-L-tartaramide (ETA), oligoethylene succinamide-L-tartaramide (EST), oligoethylene succinamide (ES), and oligodiethylenetriamino-L-tartaramide (DT). Favorable reaction conditions were also adopted to obtain low molecular weight compounds characterized by non-film-forming properties and solubility or dispersibility in environmentally friendly organic solvents. Their behavior in terms of modification of the wood surface characteristics, such as wettability, moisture absorption, and color, was analyzed using a specific diagnostic protocol to rapidly obtain preliminary, but reliable, results for optimizing a future synthesis of new and tailored protectives. The influence of different monomer units on the reactivity, solubility, and hydrophobic properties of different oligoamides was compared showing ESF (contact angle 138.2°) and DF (132.2°) as the most effective products. The study of stability to photochemical degradation confirms ESF as promising protective agents for artefacts of historical and artistic interest in place of long-chain perfluoroalkyl substances (PFAS), products currently subject to restrictions on use.

The impact of natural sunlight irradiation on the biotoxicities of different molecular sizes EfOM/SRNOM and its relationship with spectral and molecular level parameters

Natural sunlight irradiation is regarded as an efficient and low-carbon method for controlling the biotoxicity of effluents from domestic wastewater treatment plants (WWTPs). Dissolved organic matter in WWTPs effluent (EfOM) is responsible for the non-specific biotoxicity of effluent. In the present study, the variation in spectral characteristics, molecular composition, luminescent bacteria toxicity, and genotoxicity of EfOM of different molecular sizes (MOSs) during natural sunlight irradiation were investigated from a systematic perspective, and the standard natural organic matter from the Suwannee River (SRNOM) was synchronously assessed for comparative purposes. To further explore the cause of the biotoxicity changes, the relationships between the spectral or molecular level parameters (obtained from FT-ICR MS analysis) and biotoxicity were assessed using correlation analysis. The molecules in <1 kDa EfOM with lower molecular weight, higher unsaturation degree, and higher humification and fluorescence had higher luminescent bacteria toxicity under sunlight irradiation. However, in the <1 kDa SRNOM, the molecules which were characterized by higher humification and fluorescence had higher luminescent bacteria toxicity. The notable genotoxicity reduction of EfOM under sunlight irradiation was attributed to the photochemical degradation of components with a high unsaturation degree. Such findings could enable ecological safety improvement of aquatic environments using natural sunlight.

Local nanoscale phase impurities are degradation sites in halide perovskites.

Understanding the nanoscopic chemical and structural changes that drive instabilities in emerging energy materials is essential for mitigating device degradation. The power conversion efficiency of halide perovskite photovoltaic devices has reached 25.7 per cent in single-junction and 29.8 per cent in tandem perovskite/silicon cells1,2, yet retaining such performance under continuous operation has remained elusive3. Here we develop a multimodal microscopy toolkit to reveal that in leading formamidinium-rich perovskite absorbers, nanoscale phase impurities, including hexagonal polytype and lead iodide inclusions, are not only traps for photoexcited carriers, which themselves reduce performance4,5, but also, through the same trapping process, are sites at which photochemical degradation of the absorber layer is seeded. We visualize illumination-induced structural changes at phase impurities associated with trap clusters, revealing that even trace amounts of these phases, otherwise undetected with bulk measurements, compromise device longevity. The type and distribution of these unwanted phase inclusions depends on the film composition and processing, with the presence of polytypes being most detrimental for film photo-stability. Importantly, we reveal that both performance losses and intrinsic degradation processes can be mitigated by modulating these defective phase impurities, and demonstrate that this requires careful tuning of local structural and chemical properties. This multimodal workflow to correlate the nanoscopic landscape of beam-sensitive energy materials will be applicable to a wide range of semiconductors for which a local picture of performance and operational stability has yet to be established.

Environmental photochemistry on plants: recent advances and new opportunities for interdisciplinary research.

Plants play a central role in the photochemistry of chemicals in the environment. They represent a major atmospheric source of volatile organic compounds (VOCs) but also an important environmental surface for the deposition and photochemical reactions of pesticides, gaseous and particulate pollutants. In this review, we point out the role of plant leaves in these processes, as a support affecting the reactions physically and chemically and as a partner through the release of natural constituents (water, secondary metabolites). We discuss the influence of the chosen support (leaves, needle surfaces or fruit cuticles, extracted cuticular waxes and model surfaces) and other factors (additives, pesticides mixture, and secondary metabolites) on the photochemical degradation kinetics and mechanisms. We also show how plants can be a source of photochemically reactive species which can act as photosensitizers promoting the photodegradation of pesticides or the formation and aging of secondary organic aerosols (SOA) and secondary organic materials (SOM). Understanding the fate of chemicals on plants is a research area located at the interface between photochemistry, analytical chemistry, atmospheric chemistry, microbiology and vegetal physiology. Pluridisciplinary approaches are needed to deeply understand these complex phenomena in a comprehensive way. To overcome this challenge, we summarize future research directions which have been clearly overlooked until now.

Luminous custard powder – fluorescence and photochemical degradation in riboflavin

AbstractWechselwirkungen von Energie und Materie erfahren im Chemieunterricht oft nur eine geringe Beachtung, meist aufgrund fehlender konzeptioneller und experimenteller Einbindung. Die drei hier vorgestellten Experimente zeigen am Beispiel des photochemischen Abbaus des Vitamins Riboflavin, wie Fluoreszenzerscheinungen als Nachweis für Edukte und Produkte in chemischen Reaktionen dienen können. Riboflavin wird aus Puddingpulver extrahiert und anhand seiner gelben Fluoreszenz sowie der Bildung eines nicht‐fluoreszierenden, roten Komplexes bei Zugabe von Silber‐Ionen identifiziert. Durch Bestrahlung einer Riboflavin‐Lösung mit UV‐Licht bildet sich das Photoprodukt Lumichrom. Mithilfe einer dünnschichtchromatographischen Untersuchung werden Riboflavin und Lumichrom anhand ihrer Fluoreszenzfarben voneinander unterschieden. Anschließend wird der Einfluss von Temperatur, Lösungsmittel, Bestrahlungsdauer und Farbe des Bestrahlungslichts auf die Geschwindigkeit des photochemischen Abbaus untersucht.

Photodegradation of free estrogens driven by UV light: Effects of operation mode and water matrix

Estrogens are endocrine disrupting chemicals that have been frequently detected in diverse water matrices (e.g. surface water, wastewater and drinking water) and caused a series of health risks. This study was aimed at investigating the photochemical degradation of free estrogens estrone (E1), 17β-estradiol (E2), estriol (E3), and 17α-ethyl estradiol (EE2) upon the monochromatic irradiation (253.7 nm). Concerning the practical installation of photolysis treatment, exposing the impacts of photoreactor operation mode (stationary or up-flow) and the water matrix (ultrapure water or natural surface water) on the photolytic behaviour of estrogens was of high importance. The pseudo-first-order rate constants showed that E1 was the most susceptible to UV radiation among chosen estrogens due to its high molar absorption coefficient of 402.4 M−1 cm−1 and quantum yield of 0.065 mol E−1 at λ = 253.7 nm. Moreover, the up-flow mode and the surface water matrix collected from a lake in Regent's Park (London) were found to favour the photodegradation of estrogens due to the introduction of more dissolved oxygens and promotion of reactive oxygen species (ROS) formation. These findings may shed light on the photochemical behaviour of estrogens in some specific scenarios.

Biological and photochemical reactivity of dissolved organic matter in a large temperate river

AbstractLarge rivers are critical conduits from continents to oceans as they receive, produce and process huge amounts of dissolved organic matter (DOM). Yet, the relative influence of intrinsic DOM properties and extrinsic environmental properties on these processes at the ecosystem‐level is rarely studied. We assessed DOM optical properties as well as bioreactivity and photoreactivity at 40 sites along a &gt;200 km transect of the freshwater portion of the St. Lawrence River through a series of standardized microbial incubations and exposure to simulated sunlight, and then estimated in situ areal rates of processing. We found that biological and photochemical processes preferentially targeted contrasting pools of DOM, but that DOM composition had an undiscernible effect on in situ degradation rates compared to other environmental factors. Total daily processing across the whole water column ranged from 36.7 to 892.1 mg C m−2. In situ photochemical degradation was largely driven by intrinsic DOM photoreactivity rather than environmental drivers in the water. In contrast, we found a relatively constant baseline pool of biolabile DOM that appeared to be independent from changes in concentration and environmental conditions. In situ DOM processing was mostly driven by biological degradation (on average 95%), and disproportionately high biodegradation rates (2.5–4x the average) were found in a few shallower sites near effluents or islands, potentially driven by local increases in nutrient concentration and in the proportion of protein‐like DOM. These results illustrate how DOM composition and degradability interact with ambient environmental and morphological properties to dictate an ecosystem‐level reactivity of DOM.

Photochemical degradation of dexamethasone by UV/Persulphate, UV/Hydrogen peroxide and UV/free chlorine processes in aqueous solution using response surface methodology (RSM)

ABSTRACT Dexamethasone (DEX) degradation was investigated using three UV-based advanced oxidation processes combined with sodium persulphate, hydrogen peroxide, and free chlorine in aqueous solutions in a bench-scale reactor. The goal was to determine which process would be the best option in terms of DEX degradation without the subsequent generation of toxic compounds. The process performance for DEX degradation followed the UV/S2O8 2−> UV/H2O2> UV/HOCl order under equal conditions. In the UV/S2O8 2− process, sulphate radicals led to a 70.4% DEX degradation. The experimental mineral inhibitory factors showed that nitrite and bicarbonate further decrease the efficiency of the UV/S2O8 2− process. In the optimal conditions, the UV/S2O8 −2 process removed DEX by 100% and had a 74.1% mineralisation. Furthermore, the intermediates were detected using LC-MS/MS, and the cytotoxicity of the UV/S2O8 −2 process effluent was evaluated using human embryonic kidney cultured cells. The treatment of DEX solution by the UV/S2O8 −2 process significantly decreased the toxicity of the effluent. Therefore, it can be concluded that the UV/S2O8 −2 process can be a reliable process for DEX degradation and detoxification in aqueous solutions.

Photochemical Degradation of Dimethylmercury in Natural Waters.

Photochemical demethylation of dimethylmercury (DMHg) could potentially be an important source of monomethylmercury (MMHg) in sunlit water. Whether or not DMHg is photochemically degraded when dissolved in water is, however, debated. While an early study suggested DMHg dissolved in natural waters to readily degrade, later work claimed DMHg to be stable in seawater under natural sunlight and that early observations may be due to experimental artifacts. Here, we present experimental data showing that DMHg is readily degraded by photochemical processes in different natural waters (including water from a DOC-rich stream, the Baltic Sea, and the Arctic Ocean) as well as in artificial seawater and purified water. For most of the waters, the degradation rate constant (kd) for DMHg measured in indoor experiments exceeded, or was close to, the kd observed for MMHg. Outdoor incubations of DMHg in purified water and Arctic Ocean surface water further confirmed that DMHg is photochemically degraded under natural sunlight. Our study shows that DMHg is photochemically degraded in a range of natural waters and that this process may be a source of MMHg in sunlit waters where the supply or formation of DMHg is sufficient.

Resveratrol Microencapsulation into Electrosprayed Polymeric Carriers for the Treatment of Chronic, Non-Healing Wounds.

Chronic, non-healing wounds represent a challenging socio-economic burden, demanding innovative approaches for successful wound management. Resveratrol (RSV) represents a promising therapeutic candidate, but its therapeutic efficacy and clinical applicability have been hampered by its rapid degradation and/or depletion. Herein, RSV was encapsulated into poly(ε-caprolactone) (PCL) microparticles by electrospraying with the aim to prolong and preserve RSV’s release/activity, without affecting its therapeutic properties. Electrospraying led to the fabrication of spherical (2 to 10 μm in size), negatively charged (<−1 mV), and quasi-monodisperse (PDI < 0.3) microparticles, with 60% RSV release after 28 days. Microencapsulation of RSV into PCL prevented its photochemical degradation and preserved its antioxidant properties over 72 h. The RSV-PCL microparticles did not exhibit any cytotoxicity on human dermal fibroblasts. RSV released from the microparticles was biologically functional and induced a significant increase in collagen type I deposition. Furthermore, the produced RSV-PCL microparticles reduced the expression of inflammatory (IL-6, IL-8, COX-2) and proteolytic (MMP-2, MMP-9) mediators. Collectively, our data clearly illustrate the potential of electrosprayed polymeric carriers for the sustained delivery of RSV to treat chronic wounds.

Photochemical degradation of persistent organic pollutants (PCDD/FS, PCBS, PBDES, DDTS and HCB) in hexane and fish oil

This study has investigated the photochemical degradation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), polybrominated diphenylethers (PBDEs) and some organochlorine pesticides, such as hexachlorobenzene (HCB) or dichloro-diphenyl-trichloroethane (DDT) in hexane under UV irradiation at 254 nm. All pollutants were completely degraded after 3.5 h of exposition to the UV light. Moreover, this technique was applied to remove persistent organic pollutants from fish oil, with eliminations of a 34% for PCDD/Fs, 53% for PCBs, 59% for HCB, 67% for PBDEs and 73% for DDTs after 12 h of exposition to the UV light (254 nm). Dioxin-like PCBs increased their concentration after the treatment, probably due to the dehalogenation of other more chlorinated congeners. The fatty acids analysis of the fish oil revealed that the most important ω-3 fatty acids –EPA and DHA-were degraded to 67 and 70% of their initial content respectively. For these reasons elimination of persistent organic pollutants with photochemical treatment has limited applications for oils with food-purposes. However, it still can be a useful technique for decontamination of industrial oils.

Photochemical degradation of the antidepressant sertraline in aqueous solutions by UVC, UVC/H2O2, and UVC/S2O82−

Antidepressants are released into the aquatic environment because of their incomplete removal from wastewater treatment plants. In the present work, we investigated the photochemical degradation of a commonly prescribed antidepressant, namely sertraline, in aqueous matrices. The molar absorption coefficient of sertraline at 254 nm and at various pH values in the range from 4.0 to 9.0 was 444±65 L•mol–1•cm–1, while the quantum yield of its direct photolysis under UVC radiation (λ = 254 nm) was (1.7±0.1) × 10−2 mol∙einstein−1 (i.e., both values were relatively low). Next, we investigated the photochemical degradation of sertraline under UVC radiation in the presence of hydrogen peroxide, H2O2 (i.e., UVC/H2O2) or persulfate ions, S2O82− (i.e., UVC/PS). Several parameters were studied, such as the initial concentrations of the oxidants, solution pH, and the composition of the aqueous matrix (experiments were carried out in aqueous phosphate buffers, in synthetic wastewater, as well as in synthetic fresh and hydrolyzed human urine). It was found that, in all aqueous matrices, the photochemical degradation of sertraline followed pseudo first-order kinetics. The values of the observed pseudo first-order rate constants in the UVC/H2O2 and UVC/PS processes were from one to three orders of magnitude higher than the corresponding value in the UVC process. The UVC/PS process was more efficient than the UVC/H2O2 process, either in aqueous phosphate buffer solutions or in synthetic wastewaters, despite the comparable reactivity of sertraline towards hydroxyl and sulfate radicals. However, both processes resulted in partial mineralization of the compound after prolonged irradiation. In the UVC/H2O2 process, there was an optimum H2O2 concentration which depended on the aqueous matrix, while in the UVC/PS process, there was an almost linear increase in treatment efficiency as a function of PS concentration, at least in the range of concentrations studied in the present work. Solution pH in the range from 6.0 to 9.0 had a relatively negligible effect on treatment performance for both processes. In synthetic urine matrices, despite the reduction in reaction rate (the observed pseudo first-order rate constants were reduced by approximately one to two orders of magnitude), the photochemical degradation of sertraline proceeded to a relatively satisfactory degree. Finally, the calculations of the electrical energy per order and the associated cost showed that the UVC/H2O2 and UVC/PS processes are cost-efficient and suitable for full-scale applications.

Synergistic effect of nitrate on UV-chlorine photochemical degradation of carbamazepine.

We investigated the use of UV-chlorine advanced oxidation process for the removal and transformation of carbamazepine (CBZ), and its photochemical synergy with NO3- for the production of .OH towards enhancing CBZ removal in aqueous solution. Production of .OH by UV-chlorine system with/without NO3- was studied under different conditions, by using salicylic acid (SA) as the chemical probe for .OH. Initial concentration of 30 mg/L SA, 5 and 10 mg/L chlorine, and 0-10 mg/L NO3- under irradiation at 254 nm (3.026 W/L) in a photochemical reactor was used. Aqueous solutions containing 10 mg/L chlorine and spiked with 4 mg/L NO3- gave the highest reproducible generation of .OH. Using initial concentrations of 10 mg/L CBZ and 10 mg/L chlorine, 60 % CBZ was removed after 10 min of irradiation without NO3-, while 72 % CBZ was removed with 4 mg/L NO3- added. There was no noticeable CBZ removal after 10 min of irradiation in the presence of NO3- without chlorine. Corresponding dark reactions were also conducted, with no noticeable degradation of CBZ. Samples were analyzed via UHPLC, LC-MS, and TOC (total organic carbon) analyzer for CBZ and TOC concentrations respectively. Although, there was significant reduction in CBZ concentrationduring both photochemical degradation processes, the was low TOC removal (~10%) in each case. The two photochemical degradation processes also seem to generate similar degradation products indicating that the addition NO3- of the UV-chlorine process might not have changed the degradation mechanism. The results indicate that NO3- could act synergistically in a UV-chlorine system to increase CBZ removal and reduce the quantity of free chlorine required to achieve a target removal efficiency. This could facilitate reduction in the potential production of chlorinated byproducts in the system.