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Water Research Feb 2021Atrazine, a widely used herbicide, is susceptible to photolysis. The role of triplet excited states of chromophoric dissolved organic matter (CDOM*) in the photolysis of...
Atrazine, a widely used herbicide, is susceptible to photolysis. The role of triplet excited states of chromophoric dissolved organic matter (CDOM*) in the photolysis of atrazine, however, is not well understood. The direct photolysis of atrazine under irradiation sources (natural sunlight/environmentally relevant simulated solar light) and its indirect photochemical reactivity with model triplet photosensitizers (benzophenone, 2-acetonaphthone, 3'-methoxy-acetophenone, 4-carboxybenzophenone, rose bengal, methylene blue, and anthraquinone-2-sulphonate) was investigated. The reactivity of the model sensitizers and DOM (Suwannee River natural organic matter, river/lake water, and wastewater effluent), were compared. The direct photolysis quantum yield was determined as 0.0196 mol Einstein in a solar simulator and 0.00437 mol Einstein under natural sunlight. Considerable photosensitization was induced by triplet state (n-π*) model sensitizers, while insignificant effects on atrazine loss were discerned in natural organic matter even when oxygen, a triplet quencher, was removed. The triplet sensitizers benzophenone and 2-acetylnaphthone reacted with L-histidine and 2-propanol that were intended to quench/ scavenge O and hydroxyl radical OH, respectively, and benzophenone reacted with NaN as a O scavenger and furfuryl alcohol as a O trapping agent, indicating quenchers may have unanticipated effects when using model sensitizers. Atrazine loss via reaction with DOM* will be relevant only in selected conditions, and this work provides a more comprehensive view on the use of model photosensitizers to mimic triplet DOM*.
Topics: Atrazine; Hydroxyl Radical; Photolysis; Rivers; Water Pollutants, Chemical
PubMed: 33279742
DOI: 10.1016/j.watres.2020.116659 -
Environmental Science & Technology Apr 2016Photolysis of nitric acid and nitrate (HNO3/nitrate) was investigated on the surfaces of natural and artificial materials, including plant leaves, metal sheets, and...
Photolysis of nitric acid and nitrate (HNO3/nitrate) was investigated on the surfaces of natural and artificial materials, including plant leaves, metal sheets, and construction materials. The surfaces were conditioned in the outdoor air prior to experiments to receive natural depositions of ambient HNO3/nitrate and other atmospheric constituents. The photolysis rate constant (JHNO3(s)) of the surface HNO3/nitrate was measured based on the production rates of nitrous acid (HONO) and nitrogen oxides (NOx). The JHNO3(s) values, from 6.0 × 10(-6) s(-1) to 3.7 × 10(-4) s(-1), are 1 to 3 orders of magnitude higher than that of gaseous HNO3. The HONO was the major product from photolysis of HNO3/nitrate on most plant leaves, whereas NOx was the major product on most artificial surfaces. The JHNO3(s) values decreased with HNO3/nitrate surface density and could be described by a simple analytical equation. Within a typical range of HNO3/nitrate surface density in the low-NOx forested areas, photolysis of HNO3/nitrate on the forest canopy can be a significant source for HONO and NOx for the overlying atmosphere.
Topics: Atmosphere; Kinetics; Nitrates; Nitric Acid; Nitrogen Oxides; Nitrous Acid; Photolysis; Plants; Sunlight; Surface Properties
PubMed: 26936001
DOI: 10.1021/acs.est.5b05032 -
Journal of Environmental Management Feb 2019The widespread use of antibiotics in pharmaceutical therapies and agricultural practice has led to severe environmental pollution. In this study, the simultaneous...
The widespread use of antibiotics in pharmaceutical therapies and agricultural practice has led to severe environmental pollution. In this study, the simultaneous photolysis and photocatalysis behaviors of tetracycline (TC), one of the most frequently prescribed groups of antibiotics, were investigated using BiVO (BVO) supported on reduced graphene oxide (rGO). The resulting BVO/rGO nanocomposite (NC) showed prominent adsorption performance and photocatalytic ability under wide initial pH conditions (from acidic to alkaline: pH 2.5, 6.7, 9.2 and 10.5). This study analyzed the kinetics and proposed a mechanism for the photolytic and photocatalytic degradation of TC under visible light irradiation with BVO and BVO/rGO. The photolysis and photocatalytic degradation efficiency of TC was largely influenced by the solution pH and increased with increasing initial pH. The TC was stable without significant photolysis at pH 2.5, while TC photolysis increased up to 17% at pH 9.2. With further increase in the solution pH from 9.2 to 10.5, the light absorption of TC at 356 nm showed a red shift to 372 nm and new absorption peaks at around 533 nm were formed due to the formation of new colored intermediates. The photocatalytic degradation activities of TC by BVO/rGO under visible light irradiation reached 55, 67, 92 and 99% at initial pH 2.5, 6.7, 9.2 and 10.5, respectively. However, when using BVO only, the photocatalytic degradation of TC was 42, 61, 73 and 85% at pH 2.5, 6.7, 9.2 and 10.5, respectively. The great improvement of photocatalytic activity of BVO/rGO is attributed to the reduced particle size, increased adsorption ability of rGO, extended photo responding range of BVO, and efficient separation of photogenerated charge carriers, which are derived from the ultimate coverage of the BVO by the rGO.
Topics: Anti-Bacterial Agents; Catalysis; Graphite; Oxides; Photolysis
PubMed: 30529413
DOI: 10.1016/j.jenvman.2018.11.133 -
Photochemical & Photobiological... Nov 2022A photochemical precursor to the 5-endo-10,11-dihydroazepine nitrenium ion (1) was synthesized and used to characterize the intermediate by laser flash photolysis and...
A photochemical precursor to the 5-endo-10,11-dihydroazepine nitrenium ion (1) was synthesized and used to characterize the intermediate by laser flash photolysis and stable product analysis. In addition, DFT calculations were carried out on the nitrenium ion. These results were compared with earlier studies on the diphenylnitrenium ion in order to ascertain the effect of the 2 carbon bridge on the reactions and properties of 1. It is shown that the geometric constraints provided by the bridging group (a) destabilize the triplet state of 1 relative to the singlet state (b) substantially increase the lifetime of 1 relative to PhN by inhibiting the unimolecular cyclization pathway possible in the latter and (c) modestly increases the barrier for nucleophilic addition to the ring carbons.
Topics: Photolysis; Cyclization; Lasers; Density Functional Theory
PubMed: 35869409
DOI: 10.1007/s43630-022-00267-3 -
Journal of Photochemistry and... Jan 2020The photolysis of thiochrome (THC), an oxidation product of thiamine (vitamin B) (THE), used for its fluorimetric assay, has been studied in the pH range 7.0-12.0. THC...
The photolysis of thiochrome (THC), an oxidation product of thiamine (vitamin B) (THE), used for its fluorimetric assay, has been studied in the pH range 7.0-12.0. THC undergoes photooxidation to oxodihydrothiochrome (ODTHC) which is oxidized to a non-fluorescent compound (OP1) on UV irradiation. The kinetics of the consecutive first-order reactions: THC→kODTHC→kOP1, has been evaluated and the values of first-order rate constants, k (0.58-4.20 × 10, s) and k (0.05-2.03 × 10, s), at pH 7.0-12.0 have been determined. The rates of degradation of THC and ODTHC are enhanced with pH and the second-order rate constants k' and k' for the OH ion-catalyzed reaction are in the range of 0.002-58.3 M s. The quantum yields of the photolysis of THC and ODTHC in the pH range 7.0-12.0 have been determined. THC, ODTHC and OP1 have been identified by chromatographic, spectrometric and fluorimetric methods. THC and ODTHC have similar fluorescence characteristics and emit at 450 and 445 nm, respectively. THC, ODTHC and OP1 with distinct absorption maxima (370, 344 and 290 nm, respectively) have been determined by a newly developed and validated multicomponent spectrometric method during the photolysis reactions. The on-line formation of THC by the photooxidation of THE may lead to the degradation of THC and give erroneous results in the fluorimetric assay of THE. A scheme for the photolysis reactions of THC in aqueous solution is presented.
Topics: Catalysis; Fluorometry; Hydrogen-Ion Concentration; Kinetics; Oxidation-Reduction; Photolysis; Thiamine; Ultraviolet Rays
PubMed: 31927488
DOI: 10.1016/j.jphotobiol.2019.111766 -
Chemosphere Jan 2022Colloids, such as natural particulate matter and microplastics, can play a significant role in the fate and transport of organic contaminants. Specifically, these small...
Colloids, such as natural particulate matter and microplastics, can play a significant role in the fate and transport of organic contaminants. Specifically, these small nano-to micron-sized particles provide large surface area; thus, particle-aqueous interfacial chemistry becomes significant. In this work, we present an experimental investigation of interfacial photokinetics of malachite green cation (MG) adsorbed at the surface of polystyrene carboxyl (PSC) microspheres suspended in aqueous solution. Second harmonic generation (SHG), an interfacial selective laser spectroscopic tool, has been used to probe the buried interface. It is revealed that relative to the bulk, photoinduced degradation of MG is accelerated by approximately 10-fold at this noncatalytic particle surface. By measuring the SHG-based surface electronic spectra, we have also demonstrated that N-demethylated intermediates of MG remain at the interface until they are further decomposed. MG exhibits a bathochromic shift at the interface. Together with strong binding affinity and faster initial rate of photodegradation of MG at the interface, this work highlights that adsorption and surface photolysis are important pathways by which organic compounds can be transformed within the aquatic environment. Moreover, this research also stimulates further questions on the enrichment of reactive species at the colloidal-aqueous interface and their influence on facilitating decompositions of organic pollutants.
Topics: Microplastics; Photolysis; Plastics; Rosaniline Dyes
PubMed: 34461340
DOI: 10.1016/j.chemosphere.2021.131953 -
Faraday Discussions Oct 2019We describe cyclic peptide progelators which cleave in response to UV light to generate linearized peptides which then self-assemble into gel networks. Cyclic peptide...
We describe cyclic peptide progelators which cleave in response to UV light to generate linearized peptides which then self-assemble into gel networks. Cyclic peptide progelators were synthesized, where the peptides were sterically constrained, but upon UV irradiation, predictable cleavage products were generated. Amino acid sequences and formulation conditions were altered to tune the mechanical properties of the resulting gels. Characterization of the resulting morphologies and chemistry was achieved through liquid phase and standard TEM methods, combined with matrix assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS).
Topics: Biocompatible Materials; Bioprinting; Gels; Peptides, Cyclic; Photolysis; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Ultraviolet Rays
PubMed: 31549115
DOI: 10.1039/c9fd00026g -
Photochemistry and Photobiology Mar 2022The photolysis of vanillin produces a short-lived triplet state where its lifetime is controlled by efficient self-quenching (k ~ 2 × 10 m s ) which also...
The photolysis of vanillin produces a short-lived triplet state where its lifetime is controlled by efficient self-quenching (k ~ 2 × 10 m s ) which also generates radicals. Free radical reactions, including vanillin dimer formation, are responsible for the degradation of vanillin and is accompanied by yellowing of the acetonitrile solutions. Laser flash photolysis studies reveal a triplet absorbing at 390 nm, readily quenched by naphthalenes, conjugated dienes and oxygen. Vanillin is also a good singlet oxygen sensitizer as revealed by its characteristic NIR emission at 1270 nm.
Topics: Benzaldehydes; Photochemistry; Photolysis; Singlet Oxygen
PubMed: 34570372
DOI: 10.1111/php.13520 -
Water Research Nov 2021Metrafenone (MF), as a new type of benzophenone fungicide, has been widely used in agriculture and is persistent in the environment. Understanding its photochemical fate...
Metrafenone (MF), as a new type of benzophenone fungicide, has been widely used in agriculture and is persistent in the environment. Understanding its photochemical fate is essential for the comprehensive evaluation of its ecological risk. In the present work, we reported a detailed study on the photochemical transformation of MF in aqueous solution under irradiation (at λ > 290 nm using a high pressure mercury lamp). MF was relatively photo-reactive showing a low polychromatic quantum yield of photolysis (1.06 × 10, 20 µM) counterbalanced by a significant light absorption above 290 nm. A series of photoproducts were identified by high resolution mass spectrometry (HR-MS) analysis, and three different pathways, including oxidation of the methyl group, debromination and replacement of bromine by hydroxyl group were proposed. Among them, debromination was identified as the dominating process that could be achieved via homolytic C-Br bond cleavage from singlet and triplet MF, as confirmed by laser flash photolysis (LFP) experiments and density functional theory (DFT) calculations. Toxicity assessment revealed that photochemical degradation reduced the ecotoxicity of MF efficiently. Nitrate ions and humic acid promoted the MF photolysis, while bicarbonate exhibited no effect. Results obtained in this work would increase our understanding on the environmental fate of MF in sunlit surface waters.
Topics: Benzophenones; Bromine; Carbon; Fungicides, Industrial; Kinetics; Photolysis; Water Pollutants, Chemical
PubMed: 34706320
DOI: 10.1016/j.watres.2021.117775 -
Environmental Science & Technology Jun 2017Photolysis of nitric acid on the surface has been found recently to be greatly enhanced from that in the gas phase. Yet, photolysis of particulate nitrate (pNO)...
Photolysis of nitric acid on the surface has been found recently to be greatly enhanced from that in the gas phase. Yet, photolysis of particulate nitrate (pNO) associated with atmospheric aerosols is still relatively unknown. Here, aerosol filter samples were collected both near the ground surface and throughout the troposphere on board the NSF/NACR C-130 aircraft. The photolysis rate constants of pNO were determined from these samples by directly monitoring the production rates of nitrous acid (HONO) and nitrogen dioxide (NO) under UV light (>290 nm) irradiation. Scaled to the tropical noontime condition on the ground level (solar zenith angle = 0°), the normalized photolysis rate constants (j) are in the range from 6.2 × 10 s to 5.0 × 10 s with a median of 8.3 × 10 s and a mean (±1 SD) of (1.3 ± 1.2) × 10 s. Chemical compositions, specifically nitrate loading and organic matter, affect the rate of photolysis. Extrapolated to ambient pNO loading conditions, e.g. ≤ 10 nmol m, the mean j value is over 1.8 × 10 s in the suburban, rural, and remote environments. Photolysis of particulate nitrate is thus a source of HONO and NO in the troposphere.
Topics: Nitrates; Nitrogen Dioxide; Nitrogen Oxides; Nitrous Acid; Photolysis
PubMed: 28505434
DOI: 10.1021/acs.est.7b00387