Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 21.754
Filtrar
1.
Environ Sci Process Impacts ; 22(1): 12-24, 2020 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-31904051

RESUMO

Light energy is a driver for many biogeochemical element cycles in aquatic systems. The sunlight-induced photochemical reduction of ferric iron (Fe(iii) photoreduction) to ferrous iron (Fe(ii)) by either direct ligand-to-metal charge transfer or by photochemically produced radicals can be an important source of dissolved Feaq2+ in aqueous and sedimentary environments. Reactive oxygen species (ROS) are formed by a variety of light-dependent reactions. Those ROS can oxidize Fe(ii) or reduce Fe(iii), and due to their high reactivity they are key oxidants in aquatic systems where they influence many other biogeochemical cycles. In oxic waters with circumneutral pH, the produced Fe(ii) reaches nanomolar concentrations and serves as a nutrient, whereas in acidic waters, freshwater and marine sediments, which are rich in Fe(ii), the photochemically formed Fe(ii) can reach concentrations of up to 100 micromolar and be used as additional electron donor for acidophilic aerobic, microaerophilic, phototrophic and, if nitrate is present, for nitrate-reducing Fe(ii)-oxidizing bacteria. Therefore, Fe(iii) photoreduction may not only control the primary productivity in the oceans but has a tremendous impact on Fe cycling in the littoral zone of freshwater and marine environments. In this review, we summarize photochemical reactions involving Fe, discuss the role of ROS in Fe cycling, and highlight the importance of photoreductive processes in the environment.


Assuntos
Ferro , Nitratos , Fotoquímica , Bactérias , Compostos Férricos , Compostos Ferrosos , Água Doce , Oxirredução
3.
Chem Commun (Camb) ; 56(11): 1705-1708, 2020 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-31942910

RESUMO

We report ultrathin organic photovoltaic elements optimized to run photofaradaic reactions in biological conditions. We demonstrate concurrent oxygen reduction to hydrogen peroxide and glucose oxidation. The devices are powered by deep-red irradiation in the tissue transparency window. We utilize bilayers of phthalocyanine, acting as the light absorber, and perylene diimide, functioning as both electron-acceptor and the hydrogen peroxide evolution electrocatalyst. These heterojunction bilayers are stable when irradiated in simulated physiological conditions, producing photovoltages sufficient to simultaneously drive cathodic oxygen reduction to H2O2 and anodic oxidation of glucose. We find that optimization of the anode metal is critical for sustained photofaradaic reactivity. Our results demonstrate a robust "wet" thin film photovoltaic with potential for physiological applications where localized electrochemical manipulation is desired, in particular the delivery of reactive oxygen species.


Assuntos
Técnicas Eletroquímicas/métodos , Peróxido de Hidrogênio/síntese química , Imidas/química , Indóis/química , Perileno/análogos & derivados , Técnicas Eletroquímicas/instrumentação , Desenho de Equipamento , Glucose/química , Ouro/química , Imidas/efeitos da radiação , Indóis/efeitos da radiação , Luz , Membranas Artificiais , Oxirredução , Oxigênio/química , Perileno/química , Perileno/efeitos da radiação , Fotoquímica/métodos
4.
Environ Pollut ; 256: 113431, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31677867

RESUMO

Sertraline is an antidepressant drug that has been frequently reported in the aquatic environment and biota. While the research has mostly dealt with its occurrence and toxicity, there is a lack of information pertaining to its environmental transformation. The present study aimed to fill in these gaps by giving an insight into mechanisms of sertraline phototransformation in surface waters, which was recognized as the main transformation pathway for this contaminant. We performed photodegradation experiments in presence of photosensitizers or reaction quenchers to determine rate constants and used them to predict sertraline phototransformation kinetics by "Aqueous Photochemistry of Environmentally occurring Xenobiotics" (APEX) software. It was established that sertraline degrades by pseudo-first order kinetics mostly dominated by direct photolysis, while the presence of certain reactive species including •OH, CO3-• and 3CDOM* further accelerate the compound's breakdown rate. To validate the predicted results, sertraline-spiked surface water was irradiated by sunlight, where the half-life of sertraline at around 1.4 days was estimated. While following the photodegradation kinetics, we also identified five transformation products, of which three were determined in Slovenian surface waters. According to the ECOSAR toxicity prediction, these transformation products will either have comparable or lower toxicity than their parent compound.


Assuntos
Sertralina/química , Poluentes Químicos da Água/química , Água Doce/química , Meia-Vida , Cinética , Processos Fotoquímicos , Fotoquímica , Fotólise , Sertralina/análise , Software , Luz Solar , Água/química , Poluentes Químicos da Água/análise , Xenobióticos
5.
Chemosphere ; 241: 124927, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31590029

RESUMO

Plasma treated g-C3N4 (PT-g-C3N4) was obtained by a simple and rapid DBD plasma modification process on the pristine g-C3N4. Compared with the pristine g-C3N4, the grain size of the PT-g-C3N4 decreased from 99.2 nm to 57.2 nm, the specific surface area and the pore volume increased by 15% and 33.8%, respectively. Oxygen-containing groups such as -NO2 and -COOH were observed to form on the surface of PT-g-C3N4 so the hydrophilic property of PT-g-C3N4 was much higher than that of pristine g-C3N4. More importantly, the photocatalytic H2O2 production activity of PT-g-C3N4 was significantly improved on account of the treatment in plasma atmosphere for only 5 min, the H2O2 yield of which was about 13 times that of the pristine g-C3N4. Our finding is not only of great significance for effectively promoting the production of H2O2 under mild conditions, but also proposes an innovative DBD plasma method to modify the g-C3N4 photocatalyst, which effectively promotes the improvement of photocatalytic activity and provides valuable insights for catalyst modification studies.


Assuntos
Grafite/química , Peróxido de Hidrogênio/química , Compostos de Nitrogênio/química , Catálise , Interações Hidrofóbicas e Hidrofílicas , Tamanho da Partícula , Fotoquímica/métodos , Porosidade , Propriedades de Superfície
6.
Biochim Biophys Acta Proteins Proteom ; 1868(1): 140303, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31678192

RESUMO

Direct, NAD(P)H-independent regeneration of Old Yellow Enzymes represents an interesting approach for simplified reaction schemes for the stereoselective reduction of conjugated C=C-double bonds. Simply by illuminating the reaction mixtures with blue light in the presence of sacrificial electron donors enables to circumvent the costly and unstable nicotinamide cofactors and a corresponding regeneration system. In the present study, we characterise the parameters determining the efficiency of this approach and outline the current limitations. Particularly, the photolability of the flavin photocatalyst and the (flavin-containing) biocatalyst represent the major limitation en route to preparative application.


Assuntos
Mononucleotídeo de Flavina/química , NADPH Desidrogenase/química , Bacillus subtilis/enzimologia , Catálise , Cicloexanonas/química , Escherichia coli/genética , Mononucleotídeo de Flavina/efeitos da radiação , NADPH Desidrogenase/genética , NADPH Desidrogenase/efeitos da radiação , Oxirredução , Fotoquímica , Proteínas Recombinantes/química , Proteínas Recombinantes/efeitos da radiação
7.
Chemosphere ; 239: 124766, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31527001

RESUMO

Iron (Fe)-doped ZrO2 tetragonal nanoparticles were synthesized by a facile and inexpensive hydrothermal technique, that were doped with Fe3+ ions (0.1, 0.3, and 0.5 mol%) into the host lattice without altering the morphology and crystal structure of the nanoparticles. SEM and TEM investigations indicated that the morphology of ZrO2 nanoparticles did not change even after incorporation of Fe, while the band gap of semiconducting ZrO2 nanoparticles was reduced from 4.97 to 1.77 eV. Such a in band gap was responsible to harvest more photons to stimulate the generation of more electrons in the valence band, thereby enhancing the photoelectrochemical (PEC) water splitting as well as photocatalytic and photoelectrocatalytic activities in the photodegradation of Rhodamine B. The 0.3 mol%-doped ZrO2 electrode showed enhanced photocurrent density (0.07 × 10-3 A/cm2), that was 45-times greater than the pure sample. The electrochemical impedance spectroscopy (EIS) confirmed that 0.3 mol%-doped ZrO2 exhibited the best charge transfer characteristics, which increased with PEC water splitting activity. The maximum photocurrent density and long-term photo-stability were achieved in the light on-off states.


Assuntos
Corantes/isolamento & purificação , Ferro/química , Nanopartículas Metálicas/química , Rodaminas/isolamento & purificação , Zircônio/química , Catálise , Corantes/química , Eletrodos , Poluentes Ambientais/química , Poluentes Ambientais/isolamento & purificação , Fotoquímica/instrumentação , Fotoquímica/métodos , Fotólise , Pontos Quânticos/química , Rodaminas/química , Água/química
8.
Talanta ; 206: 120242, 2020 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-31514896

RESUMO

High performance liquid chromatography (HPLC) post-column photochemical reaction (PR) coupled capacitively coupled contactless conductivity detector (C4D) was used for the first time in analysis of weak ultraviolet (UV)-absorbing, non-fluorescence and nonpolar compound. A series of conditions including the radiation power of light source, the length of the reaction tube and the thickness of detection tube were investigated. HPLC-PR-C4D system was successfully applied to the determination of Cyclosporin A (CsA). Consequently, under optimal conditions, the detection system exhibited a detection limit of 0.04 µg/mL and wide linear range from 0.5 µg/mL to 100 µg/mL for CsA detection. Application of the HPLC-PR- C4D system to pharmaceutical formulation and biological samples revealed the system developed maybe reliably applied to clinical studies.


Assuntos
Cromatografia Líquida de Alta Pressão/métodos , Ciclosporina/sangue , Fotoquímica/métodos , Cromatografia Líquida de Alta Pressão/instrumentação , Ciclosporina/efeitos da radiação , Humanos , Imunossupressores/sangue , Imunossupressores/efeitos da radiação , Limite de Detecção , Fotoquímica/instrumentação
10.
J Chromatogr B Analyt Technol Biomed Life Sci ; 1130-1131: 121788, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31670109

RESUMO

Multilayer print designs are commonly used in commercial food packaging to attract consumers. UV-curable ink is generally used in this type of printing due to its ease of application, space saving, and rapid drying; however, there have been a number of health alerts related to the contamination of food by photoinitiators in UV-curable ink. In this study, we established a multi-analyte method by which to detect 30 photoinitiators simultaneously. We then applied this method to the analysis of five breakfast cereals and ten types of packaged juice to detect the presence of photoinitiator contamination. Sample treatment was performed using the QuEChERS (quick, easy, cheap, effective, rugged, and safe) method for the extraction of photoinitiators. Chromatographic separation of two isomers, methylbenzophenone (MBP) and isopropylthioxanthone (ITX), was achieved using a pentafluorophenyl propyl (PFP) column (1.7 µm, 100 × 2.1 mm i.d.) and MeOH: 5 mM formic acid-ammonium formate (pH 4.0) in gradient elution. The average recovery of photoinitiators from cereal was between 62.0 and 120.3%, with a coefficient of variation between 0.4 and 14.4%. The average recovery of photoinitiators from packaged juices was between 84.4 and 122.9% with a coefficient of variation between 0.5 and 9.5%. The contamination results were as follows: 13.1 ng/g triphenyl phosphate (TPP) was detected in one breakfast cereal, and 2-hydroxy-4-methoxy benzophenone (BP-3), 1-hydroxycyclohexyl phenyl-ketone (Irgacure 184), methyl-2-benzoylbenzoate (MOBB), and 2,4-diethyl-9H-thioxanthen-9-one (DETX) were detected in one of the packaged juices at levels ranging from 2.2 to 152.9 ng/g.


Assuntos
Grão Comestível/química , Contaminação de Alimentos/análise , Embalagem de Alimentos , Sucos de Frutas e Vegetais/análise , Tinta , Benzofenonas/análise , Desjejum , Cromatografia Líquida de Alta Pressão , Grão Comestível/normas , Sucos de Frutas e Vegetais/normas , Modelos Lineares , Fotoquímica , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Espectrometria de Massas em Tandem , Tioxantenos/análise , Xantonas/análise
11.
Nat Commun ; 10(1): 5123, 2019 11 12.
Artigo em Inglês | MEDLINE | ID: mdl-31719532

RESUMO

Lignin is a major component of lignocellulosic biomass. Although it is highly recalcitrant to break down, it is a very abundant natural source of valuable aromatic carbons. Thus, the effective valorisation of lignin is crucial for realising a sustainable biorefinery chain. Here, we report a compartmented photo-electro-biochemical system for unassisted, selective, and stable lignin valorisation, in which a TiO2 photocatalyst, an atomically dispersed Co-based electrocatalyst, and a biocatalyst (lignin peroxidase isozyme H8, horseradish peroxidase) are integrated, such that each system is separated using Nafion and cellulose membranes. This cell design enables lignin valorisation upon irradiation with sunlight without the need for any additional bias or sacrificial agent and allows the protection of the biocatalyst from enzyme-damaging elements, such as reactive radicals, gas bubbles, and light. The photo-electro-biochemical system is able to catalyse lignin depolymerisation with a 98.7% selectivity and polymerisation with a 73.3% yield using coniferyl alcohol, a lignin monomer.


Assuntos
Fontes de Energia Bioelétrica , Lignina/química , Fotoquímica , Luz Solar , Biopolímeros/biossíntese , Reatores Biológicos , Dimerização , Peróxido de Hidrogênio/análise , Polimerização
12.
Analyst ; 144(21): 6193-6196, 2019 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-31577279

RESUMO

We here describe a photocurrent generation system exploiting gold nanoparticles (AuNPs) that cover perylenediimide-DNA complexes on electrode surfaces. Enhanced photocurrents were generated by the irradiation of the AuNPs, attributed to the efficient excitation of the perylenediimides by a local electric field on the surface of the AuNPs.


Assuntos
DNA/química , Técnicas Eletroquímicas/métodos , Nanopartículas Metálicas/química , Fotoquímica/métodos , Técnicas Eletroquímicas/instrumentação , Eletrodos , Ouro/química , Ouro/efeitos da radiação , Imidas/química , Imidas/efeitos da radiação , Luz , Nanopartículas Metálicas/efeitos da radiação , Perileno/análogos & derivados , Perileno/química , Perileno/efeitos da radiação
13.
Environ Int ; 133(Pt A): 105095, 2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-31518929

RESUMO

Natural SPA waters and their environments were known since ancient times and used for health or recreational purposes in different societies, worldwide. The composition and uses of these spring waters may not allow standard disinfection in pools, representing a challenge for hygiene management. Several safety and quality procedures were proposed, but a systematic approach is still needed. Here, we focus on alternative strategies to provide hints for developing a sustainable Water Safety Plan, based on intrinsic water properties and photocatalytic materials. The antimicrobial activity of four different SPA waters with high mineral content and one drinkable spring water with a low mineral content, was assessed and then tested for the additional bactericidal activity of Titanium Dioxide (TiO2) nanomaterials and/or light exposure at different wavelengths (200-635 nm). A native antibacterial activity was observed in all high mineral content waters, with a CFU reduction of 75-80%. The bactericidal action of TiO2 showed an additional incremental effect, with a reduction of over 99% within 2-5 h. Interestingly, the antibacterial photocatalytic effect was detected also in the visible light range, with a possible pick around 450-455 nm, blue-light. Based on observed results, we propose a model for developing a water safety plan, considering water properties and bather exposure. This candidate approach is personalized on water composition and pool use, trying to avoid chemical disinfectants. Photocatalytic nanotechnologies represent one of the promising alternative treatments and can provide novel perspectives for a sustainable managing of natural SPA water hygiene.


Assuntos
Desinfecção , Águas Minerais/microbiologia , Nascentes Naturais/microbiologia , Purificação da Água/métodos , Desinfecção/métodos , Nanotecnologia , Fotoquímica , Titânio/química
14.
Environ Sci Technol ; 53(21): 12425-12432, 2019 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-31550134

RESUMO

The photochemistry of pyruvic acid (PA) in aqueous atmospheric particles contributes to the production of secondary organic aerosols. This work investigates the fate of ketyl and acetyl radicals produced during the photolysis (λ ≥ 305 nm) of 5-100 mM PA under steady state [O2(aq)] = 260 µM (1.0 ≤ pH ≤ 4.5) for photon fluxes between 1 and 10 suns. The radicals diffuse quickly into the water/air interface of microbubbles and react with dissolved O2 to produce singlet oxygen (1O2*). Furfuryl alcohol is used to trap and bracket the steady-state production of 2 × 10-12 ≤ [1O2*] ≤ 1 × 10-11 M. Ion chromatography mass spectrometry shows that 2,3-dimethyltartaric acid (DMTA), 2-(3-oxobutan-2-yloxy)-2-hydroxypropanoic acid (oxo-C7 product), and 2-(1-carboxy-1-hydroxyethoxy)-2-methyl-3-oxobutanoic acid (oxo-C8 product) are formed under all conditions investigated. The sigmoidal dependence of initial reaction rates with pH resembles the dissociation curve of PA. For increasing photon fluxes, the branching ratio of products shifts away from the radical recombination that favors DMTA toward multistep radical chemistry forming more complex oxocarboxylic acids (oxo-C7 + oxo-C8). The large steady-state production of 1O2 indicates that PA in aerosols can be a significant source of atmospheric oxidants on par with natural organic matter.


Assuntos
Ácido Pirúvico , Oxigênio Singlete , Concentração de Íons de Hidrogênio , Oxigênio , Fotoquímica , Fotólise
15.
Molecules ; 24(18)2019 Sep 12.
Artigo em Inglês | MEDLINE | ID: mdl-31547232

RESUMO

Use of sonication for designing and fabricating reactors, especially the deposition of catalysts inside a microreactor, is a modern approach. There are many reports that prove that a microreactor is a better setup compared with batch reactors for carrying out catalytic reactions. Microreactors have better energy efficiency, reaction rate, safety, a much finer degree of process control, better molecular diffusion, and heat-transfer properties compared with the conventional batch reactor. The use of microreactors for photocatalytic reactions is also being considered to be the appropriate reactor configuration because of its improved irradiation profile, better light penetration through the entire reactor depth, and higher spatial illumination homogeneity. Ultrasound has been used efficiently for the synthesis of materials, degradation of organic compounds, and fuel production, among other applications. The recent increase in energy demands, as well as the stringent environmental stress due to pollution, have resulted in the need to develop green chemistry-based processes to generate and remove contaminants in a more environmentally friendly and cost-effective manner. It is possible to carry out the synthesis and deposition of catalysts inside the reactor using the ultrasound-promoted method in the microfluidic system. In addition, the synergistic effect generated by photocatalysis and sonochemistry in a microreactor can be used for the production of different chemicals, which have high value in the pharmaceutical and chemical industries. The current review highlights the use of both photocatalysis and sonochemistry for developing microreactors and their applications.


Assuntos
Fotoquímica/instrumentação , Sonicação/métodos , Catálise , Desenho de Equipamento , Microfluídica/instrumentação , Nanopartículas/química , Fotoquímica/métodos , Ultrassom/instrumentação , Ultrassom/métodos
16.
J Synchrotron Radiat ; 26(Pt 5): 1432-1447, 2019 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-31490131

RESUMO

The European X-ray Free-Electron Laser (EuXFEL) delivers extremely intense (>1012 photons pulse-1 and up to 27000 pulses s-1), ultrashort (<100 fs) and transversely coherent X-ray radiation, at a repetition rate of up to 4.5 MHz. Its unique X-ray beam parameters enable novel and groundbreaking experiments in ultrafast photochemistry and material sciences at the Femtosecond X-ray Experiments (FXE) scientific instrument. This paper provides an overview of the currently implemented experimental baseline instrumentation and its performance during the commissioning phase, and a preview of planned improvements. FXE's versatile instrumentation combines the simultaneous application of forward X-ray scattering and X-ray spectroscopy techniques with femtosecond time resolution. These methods will eventually permit exploitation of wide-angle X-ray scattering studies and X-ray emission spectroscopy, along with X-ray absorption spectroscopy, including resonant inelastic X-ray scattering and X-ray Raman scattering. A suite of ultrafast optical lasers throughout the UV-visible and near-IR ranges (extending up to mid-IR in the near future) with pulse length down to 15 fs, synchronized to the X-ray source, serve to initiate dynamic changes in the sample. Time-delayed hard X-ray pulses in the 5-20 keV range are used to probe the ensuing dynamic processes using the suite of X-ray probe tools. FXE is equipped with a primary monochromator, a primary and secondary single-shot spectrometer, and a timing tool to correct the residual timing jitter between laser and X-ray pulses.


Assuntos
Lasers , Fotoquímica/instrumentação , Espectrometria por Raios X/instrumentação , Calibragem , Desenho de Equipamento , Fótons , Espalhamento de Radiação , Raios X
17.
Nat Protoc ; 14(9): 2672-2690, 2019 09.
Artigo em Inglês | MEDLINE | ID: mdl-31391579

RESUMO

Understanding the photoinduced electron-transfer process is of paramount importance for realizing efficient solar energy conversion. It is rather difficult to clarify the link between the specific properties and the photoelectrochemical performance of an individual component in an ensemble system because data are usually presented as averages because of interplay of the heterogeneity of the bulk system. Here, we report a step-by-step protocol to fabricate an ultrasensitive photoelectrochemical platform for real-time detection of the intrinsic photoelectrochemical behaviors of a single entity with picoampere and sub-millisecond sensitivity. Using a micron-thickness nanoparticulate TiO2-filmed Au ultramicroelectrode (UME) as the electron-transport electrode, photocurrent transients can be observed for each individual dye-tagged oxide semiconductor nanoparticle collision associated with a single-entity photoelectrochemical reaction. This protocol allows researchers to obtain high-resolution photocurrent signals to quantify the photoinduced electron-transfer properties of an individual entity, as well as to precisely process the data obtained. We also include procedures for dynamic light scattering (DLS) analysis, transmission electron microscopy (TEM) imaging and collision frequency-concentration correlation to confirm that the photoelectrochemical collision events occur at an unambiguously single-entity level. The time required for the entire protocol is ~36 h, with a single-entity photoelectrochemical measurement taking <1 h to complete for each independent experiment. This protocol requires basic nanoelectrochemistry and nanotechnology skills, as well as an intermediate-level understanding of photoelectrochemistry.


Assuntos
Técnicas Eletroquímicas/métodos , Nanotecnologia/métodos , Fotoquímica/métodos , Técnicas Eletroquímicas/instrumentação , Elétrons , Desenho de Equipamento , Imagem Molecular , Nanoestruturas/química , Nanotecnologia/instrumentação , Fotoquímica/instrumentação , Pontos Quânticos/química , Titânio/química
18.
Environ Pollut ; 252(Pt B): 1863-1871, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31369942

RESUMO

Alternative transportation fuels (ATFs) can reduce air pollution. However, the influence of conventional fuels-diesel and gasoline, and particularly ATFs on photochemical air pollution is not well-characterized, limiting assessments of ATFs and air quality. This is mainly due to frequent use of lumped chemical mechanisms by related atmospheric modeling. Here we hypothesized that applying a chemical mechanism that is specifically developed according to both emission fractions and photochemical ozone creation potential of volatile organic compounds (VOCs) is key to gaining reliable insights into the impact of transportation fuels on photochemistry. We used a heterogeneous chemical mechanism with 927 reactions and relatively detailed emission inventories to specifically meet the requirements for reliable simulation of the effect of exhaust emissions from vehicles fueled by selected model fuels-diesel, gasoline, and mixtures of 15% gasoline with 85% ethanol (E85) or 85% methanol (M85)-on photochemistry. These dispersion-box model simulations revealed a strong influence of atmospheric background balance between VOCs and nitrogen oxides (NOX = [NO] + [NO2]) on the impact of exhaust emissions on photochemistry, with higher tendency toward ozone (O3) formation or destruction for more VOC-limited or NOX-limited conditions, respectively. Accordingly, higher [NOX]/[VOC] exhaust emission, such as from diesel and M85, resulted in lower O3, not only locally but also downwind of the emission. This offers a new perspective and measure for transportation fuel assessment. Rapid conversion of O3 to hydroxyl and hydroperoxyl radicals downwind of the exhaust emission indicates the importance of simulating the impact of road transportation on photochemistry at high spatial and temporal resolution. Peroxyacetyl nitrate formation was more sensitive to VOC emission under VOC-limited conditions than to NOX emission under NOX-limited conditions. Secondary formaldehyde dominated over primary emitted formaldehyde several minutes after emission. These findings should be verified using a 3D modeling study under varying meteorological conditions.


Assuntos
Poluentes Atmosféricos/análise , Poluição do Ar/análise , Gasolina/análise , Óxidos de Nitrogênio/análise , Ozônio/análise , Emissões de Veículos/análise , Radical Hidroxila/análise , Modelos Teóricos , Fotoquímica , Transportes , Compostos Orgânicos Voláteis/análise
19.
Environ Sci Technol ; 53(18): 10676-10684, 2019 Sep 17.
Artigo em Inglês | MEDLINE | ID: mdl-31418557

RESUMO

In contrast to summer smog, the contribution of photochemistry to the formation of winter haze in northern mid-to-high latitude is generally assumed to be minor due to reduced solar UV and water vapor concentrations. Our comprehensive observations of atmospheric radicals and relevant parameters during several haze events in winter 2016 Beijing, however, reveal surprisingly high hydroxyl radical oxidation rates up to 15 ppbv/h, which is comparable to the high values reported in summer photochemical smog and is two to three times larger than those determined in previous observations during winter in Birmingham (Heard et al. Geophys. Res. Lett. 2004, 31, (18)), Tokyo (Kanaya et al. J. Geophys. Res.: Atmos. 2007, 112, (D21)), and New York (Ren et al. Atmos. Environ. 2006, 40, 252-263). The active photochemistry facilitates the production of secondary pollutants. It is mainly initiated by the photolysis of nitrous acid and ozonolysis of olefins and maintained by an extremely efficiently radical cycling process driven by nitric oxide. This boosted radical recycling generates fast photochemical ozone production rates that are again comparable to those during summer photochemical smog. The formation of ozone, however, is currently masked by its efficient chemical removal by nitrogen oxides contributing to the high level of wintertime particles. The future emission regulations, such as the reduction of nitrogen oxide emissions, therefore are facing the challenge of reducing haze and avoiding an increase in ozone pollution at the same time. Efficient control strategies to mitigate winter haze in Beijing may require measures similar as implemented to avoid photochemical smog in summer.


Assuntos
Poluentes Atmosféricos , Ozônio , Pequim , New York , Fotoquímica , Smog
20.
J Agric Food Chem ; 67(44): 12155-12163, 2019 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-31415171

RESUMO

Photoresponsive hydrogels from polysaccharides and Fe(III) were used as a new system to capture and release PO43- from waste solutions. Uptake of 0.6-1.5 mg of phosphate per gram of hydrogels was determined from 800 ppm phosphate solutions (pH 4.8-9.0). These beads also captured 1.2 mg g-1 of phosphate from animal waste (raw manure, 727 ppm phosphate, pH 7.6), which accounted for above 80% phosphate uptake. Irradiation of phosphate-loaded hydrogels degraded the gels due to the photochemistry of the Fe(III)-carboxylates, giving controlled phosphate release (∼81% after 7 days). No release (<2% after 7 days) was seen in the dark. Kale plant trials showed complete degradation of the hydrogels in ∼2 weeks under greenhouse conditions. Biomass analysis of kale treated with phosphate-loaded beads compared to controls indicated no signs of toxicity. These results show that Fe(III)-polysaccharide hydrogels were able to reclaim phosphates from waste solutions and can be used as a controlled-release fertilizer.


Assuntos
Preparações de Ação Retardada/química , Compostos Férricos/química , Fertilizantes/análise , Hidrogéis/química , Fosfatos/química , Polissacarídeos/química , Águas Residuárias/química , Adsorção , Animais , Brassica/crescimento & desenvolvimento , Brassica/metabolismo , Preparações de Ação Retardada/metabolismo , Esterco/análise , Fosfatos/metabolismo , Fotoquímica
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA