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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 -
Environmental Technology Nov 2021In the present study, the HS photolysis using the self-made high-frequency discharge electrodeless lamp (light distribution was 90% at 254 nm and 10% at 185 nm) was...
In the present study, the HS photolysis using the self-made high-frequency discharge electrodeless lamp (light distribution was 90% at 254 nm and 10% at 185 nm) was studied and simulated by MATLAB software. Firstly, the effects of the initial HS concentration, irradiation time, oxygen content and relative humidity on HS photolysis efficiency were experimentally investigated. The results indicated that the photolysis efficiency decreased from 100% to 90.13% with the increase in the initial concentration from 3 to 30 mg/m, and the main product was HSO. With the relative humidity increased from 0% to 99%, HS photolysis efficiency was obviously improved under different atmospheres (O> air > Ar), indicating the significant effect of relative humidity and oxygen concentration. The simulation results were consistent with the experimental results, indicating the feasibility of the simulation model. Moreover, based on the photoreactions, model simulation and equilibrium analysis of sulphur species, the photodegradation pathway of HS was further inferred. HS was oxidized to HSO by O and other strong oxidizing radicals excited by 185 nm UV light.
Topics: Oxidation-Reduction; Photolysis; Ultraviolet Rays
PubMed: 32290784
DOI: 10.1080/09593330.2020.1756421 -
Chemosphere Aug 2020The photolysis dynamics of m-fluorophenol (m-FPhOH) and o-fluorophenol (o-FPhOH) have been investigated with time-resolved velocity map imaging (TR-VMI) and...
The photolysis dynamics of m-fluorophenol (m-FPhOH) and o-fluorophenol (o-FPhOH) have been investigated with time-resolved velocity map imaging (TR-VMI) and time-resolved ion-yield (TR-IY) techniques. Following excitation to the origin of S (ππ∗) state of m- and o-FPhOH, H atoms elimination mediated by tunneling through the potential barrier under the S (ππ∗)/S (πσ∗) conical intersection (CI) has been observed as a Gaussian feature signal centered at a total kinetic energy release (TKER) of ∼6000 cm for both molecules. The quantum tunneling mechanism has been identified as the main decay pathway of S state for m-FPhOH, and the tunneling lifetime of 2.1 ns has been obtained from the TR-VMI measurements of H fragments. This tunneling mechanism is further confirmed by the studies on the selective O-H deuterated species, m-FPhOD, and consolidated by our theoretical calculations. However, the photolysis dynamics is quite different for the photoexcited o-FPhOH. The much lower yield of the H atoms originating from tunneling hinders the extraction of a reliable tunneling lifetime for o-FPhOH. Our theoretical calculations exhibit a broader and higher potential barrier exists beneath the S/S CI of o-FPhOH, which increase the difficulty for tunneling. Furthermore, the special existence of intramolecular hydrogen bond in o-FPhOH is probably also the key factor that affects the tunneling rate, which would restrict the O-H stretch motion.
Topics: Hydrogen Bonding; Models, Chemical; Phenols; Photolysis
PubMed: 32464759
DOI: 10.1016/j.chemosphere.2020.126747 -
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 -
Chemosphere Jan 2019Advanced oxidation processes (AOPs) are an attractive method to decompose dye-containing wastewaters, because they avoid issues of secondary pollution. In particular, a...
Advanced oxidation processes (AOPs) are an attractive method to decompose dye-containing wastewaters, because they avoid issues of secondary pollution. In particular, a vacuum-ultraviolet (VUV) process is the simplest method, because an oxidation accelerator or a catalyst is not required. Conventional VUV sources with wavelengths of 185 nm or 172 nm have been used. We predicted that a shorter wavelength VUV process would have a higher ability to decompose dyes in wastewater. We developed a new planar light source that could emit a resonance line at 147 nm and a broad molecular line at 172 nm. The irradiance was 8.7 mW/cm at a distance of 20 mm from the emission surface to the UV power meter. We then conducted photocatalytic experiments of an Indigo Carmine solution at 3.33 × 10 mol/L to confirm the decomposition abilities of the developed light source, an excimer lamp of 172 nm and a Hg lamp of 254 nm. From the HPLC results, changes in Indigo Carmine concentration with the developed light source were equivalent to those with the excimer lamp. However, the residual ratio of total organic carbon (TOC) with the developed light source was lower than those with the other lamps. Therefore, a wavelength of 147 nm is superior to the conventional wavelength of 172 nm for Indigo Carmine decomposition. In addition, the developed light source emits VUV from only one side, which is a flat emitting surface. Consequently, the developed light source would have reduced manufacturing and maintenance costs compared to current VUV processing equipment.
Topics: Catalysis; Equipment Design; Indigo Carmine; Oxidation-Reduction; Photolysis; Ultraviolet Rays; Vacuum; Wastewater
PubMed: 30261418
DOI: 10.1016/j.chemosphere.2018.09.102 -
Environmental Science. Processes &... Jan 2022UV photolysis has increasingly been utilized for disinfection of water-born pathogens in wastewater. During disinfection, wastewater-derived trace organic contaminants,...
UV photolysis has increasingly been utilized for disinfection of water-born pathogens in wastewater. During disinfection, wastewater-derived trace organic contaminants, such as pharmaceuticals and personal care products (PPCPs), may be subjected to direct photolysis and indirect photolysis sensitized by wastewater constituents such as nitrite (NO). Herein, we reported the direct photolysis and NO-sensitized indirect photolysis of four phenolic contaminants commonly observed in wastewaters (, bisphenol A (BPA), acetaminophen (ATP), salbutamol (SAL), and 2,4-dihydroxybenzophenone (BP1)). Spectroscopic characterization and quantum yield measurement were carried out to evaluate the photochemical reactivity of these phenolic compounds. In NO-sensitized photolysis, the relative contribution of direct and indirect photolysis was quantified by light screening factor calculation and radical quenching studies. The experimental results highlight the important roles of HO˙ and NO˙ in the NO-sensitized photolysis of phenolic compounds. A series of intermediate products, including hydroxylated, nitrated, nitrosated, dimerized, and alkyl chain cleavage products, were identified by solid phase extraction (SPE) combined with high-resolution mass spectrometry (HRMS) analyses. On the basis of identified products, the underlying mechanisms and transformation pathways for NO-sensitized photolysis of these phenolic compounds were elucidated. The second-order rate constants of BPA, SAL, BP1 with NO˙ were calculated to be 2.25 × 10, 1.35 × 10 and 2.44 × 10 M s, respectively, by kinetic modeling. Suwanee River natural organic matter (SRNOM) played complex roles in the direct and NO-sensitized photolysis of phenolic compounds by serving as a photosensitizer, light screening and radical quenching agent. Wastewater constituents, such as NO and EfOM, could accelerate direct and NO-sensitized photolysis of BPA, SAL, and BP1 in the wastewater matrix. Our results suggest that NO at the WWTP effluent-relevant level can sensitize the photolysis of effluent-derived phenolic contaminants during the UV disinfection process; however, the formation of potentially carcinogenic and mutagenic nitrated/nitrosated derivatives should be scrutinized.
Topics: Nitrates; Nitrites; Photolysis; Wastewater; Water Pollutants, Chemical
PubMed: 34981110
DOI: 10.1039/d1em00381j -
Journal of the American Chemical Society Jul 2022Photolabile protecting groups (PPGs) enable the precise activation of molecular function with light in many research areas, such as photopharmacology, where remote...
Photolabile protecting groups (PPGs) enable the precise activation of molecular function with light in many research areas, such as photopharmacology, where remote spatiotemporal control over the release of a molecule is needed. The design and application of PPGs in recent years have particularly focused on the development of molecules with high molar absorptivity at long irradiation wavelengths. However, a crucial parameter, which is pivotal to the efficiency of uncaging and which has until now proven highly challenging to improve, is the photolysis quantum yield (QY). Here, we describe a novel and general approach to greatly increase the photolysis QY of heterolytic PPGs through stabilization of an intermediate chromophore cation. When applied to coumarin PPGs, our strategy resulted in systems possessing an up to a 35-fold increase in QY and a convenient fluorescent readout during their uncaging, all while requiring the same number of synthetic steps for their preparation as the usual coumarin systems. We demonstrate that the same QY engineering strategy applies to different photolysis payloads and even different classes of PPGs. Furthermore, analysis of the DFT-calculated energy barriers in the first singlet excited state reveals valuable insights into the important factors that determine photolysis efficiency. The strategy reported herein will enable the development of efficient PPGs tailored for many applications.
Topics: Cations; Coumarins; Photolysis
PubMed: 35775744
DOI: 10.1021/jacs.2c04262 -
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 -
Ecotoxicology and Environmental Safety Aug 1982
Topics: Gas Chromatography-Mass Spectrometry; Half-Life; Hydrocarbons, Chlorinated; Photolysis
PubMed: 7117186
DOI: 10.1016/0147-6513(82)90049-5 -
Chemosphere Nov 2022Abiotic photochemical reactions are usually very important degradation pathways for biorecalcitrant pollutants in surface freshwaters. Therefore, the assessment of...
Abiotic photochemical reactions are usually very important degradation pathways for biorecalcitrant pollutants in surface freshwaters. Therefore, the assessment of photolytic lifetimes of contaminants helps estimate their impact on aquatic systems. This is commonly carried out by combining irradiation experiments and modelling, where the latter considers mathematical functions with polychromatic parameters, such as sunlight spectra, photolysis quantum yields (when Kasha's rule does not hold), and absorption coefficients. With the polychromatic approach, the photolytic lifetime is calculated by solving several integrals, which requires quite demanding modelling resources. In this work, we applied a recently developed approach, which is based on the equivalent monochromatic wavelength (EMW) approximation, to compute the direct-photolysis lifetimes of a range of >40 pollutants in inland waters. The EMW approximation allowed for easier modelling procedure, at the same time providing very good agreement with the polychromatic system. To further show EMW potentialities, lifetimes of three contaminants were mapped over the Piedmont region (NW Italy), as an example of how easy it becomes to geographically EMW-assess the potential of watercourses, to get photochemically decontaminated from pollutants.
Topics: Fresh Water; Kinetics; Photochemical Processes; Photolysis; Water Pollutants, Chemical
PubMed: 35964728
DOI: 10.1016/j.chemosphere.2022.135982