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1.
Nat Commun ; 11(1): 4193, 2020 08 21.
Artigo em Inglês | MEDLINE | ID: mdl-32826921

RESUMO

Photochemical reactions are a powerful tool in (bio)materials design due to the spatial and temporal control light can provide. To extend their applications in biological setting, the use of low-energy, long wavelength light with high penetration propertiesis required. Further regulation of the photochemical process by additional stimuli, such as pH, will open the door for construction of highly regulated systems in nanotechnology- and biology-driven applications. Here we report the green light induced [2+2] cycloaddition of a halochromic system based on a styrylquinoxaline moiety, which allows for its photo-reactivity to be switched on and off by adjusting the pH of the system. Critically, the [2+2] photocycloaddition can be activated by green light (λ up to 550 nm), which is the longest wavelength employed to date in catalyst-free photocycloadditions in solution. Importantly, the pH-dependence of the photo-reactivity was mapped by constant photon action plots. The action plots further indicate that the choice of solvent strongly impacts the system's photo-reactivity. Indeed, higher conversion and longer activation wavelengths were observed in water compared to acetonitrile under identical reaction conditions. The wider applicability of the system was demonstrated in the crosslinking of an 8-arm PEG to form hydrogels (ca. 1 cm in thickness) with a range of mechanical properties and pH responsiveness, highlighting the potential of the system in materials science.


Assuntos
Reação de Cicloadição/métodos , Hidrogéis/química , Luz , Processos Fotoquímicos , Animais , Catálise , Sobrevivência Celular , Fibroblastos , Concentração de Íons de Hidrogênio , Camundongos , Fótons , Polímeros/química , Reologia
2.
Nature ; 584(7819): 75-81, 2020 08.
Artigo em Inglês | MEDLINE | ID: mdl-32760044

RESUMO

Chemical reactions that reliably join two molecular fragments together (cross-couplings) are essential to the discovery and manufacture of pharmaceuticals and agrochemicals1,2. The introduction of amines onto functionalized aromatics at specific and pre-determined positions (ortho versus meta versus para) is currently achievable only in transition-metal-catalysed processes and requires halogen- or boron-containing substrates3-6. The introduction of these groups around the aromatic unit is dictated by the intrinsic reactivity profile of the method (electrophilic halogenation or C-H borylation) so selective targeting of all positions is often not possible. Here we report a non-canonical cross-coupling approach for the construction of anilines, exploiting saturated cyclohexanones as aryl electrophile surrogates. Condensation between amines and carbonyls, a process that frequently occurs in nature and is often used by (bio-)organic chemists7, enables a predetermined and site-selective carbon-nitrogen (C-N) bond formation, while a photoredox- and cobalt-based catalytic system progressively desaturates the cyclohexene ring en route to the aniline. Given that functionalized cyclohexanones are readily accessible with complete regiocontrol using the well established carbonyl reactivity, this approach bypasses some of the frequent selectivity issues of aromatic chemistry. We demonstrate the utility of this C-N coupling protocol by preparing commercial medicines and by the late-stage amination-aromatization of natural products, steroids and terpene feedstocks.


Assuntos
Compostos de Anilina/síntese química , Hidrogênio/química , Processos Fotoquímicos , Aminação , Aminas/química , Compostos de Anilina/química , Produtos Biológicos/síntese química , Produtos Biológicos/química , Catálise/efeitos da radiação , Cicloexanonas/química , Oxirredução/efeitos da radiação , Processos Fotoquímicos/efeitos da radiação , Esteroides/síntese química , Esteroides/química , Terpenos/síntese química , Terpenos/química
3.
Chemosphere ; 257: 127161, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32526465

RESUMO

Sediments exposed to sunlight can serve as an important source of dissolved organic carbon (DOC) and nutrients to overlying waters. However, the photochemical release processes of dissolved organic matter (DOM) from resuspended sediments and the characteristics of photoreleased DOM are not fully understood. In this study, excitation-emission matrix fluorescence combined with parallel factor analysis (EEMs-PARAFAC) was used to study the photochemical release of DOM qualitatively and quantitatively. The EEMs-PARAFAC demonstrated that the photoreleased DOM is dominated by humic-like substances, and the photorelease process could be consist of the photoproduction and photodegradation of DOM. The concurrent photodegradation may result in the underestimation of photoreleased DOM. Moreover, the significant increases in DOC content and fluorescence intensity of humic-like components along with increasing nitrate and ferric ion indicated that nitrate and ferric ion could facilitate the photoproduction of DOM through the photochemical produced hydroxyl radical. However, the decreases in DOC and fluorescence intensity were also observed at high concentration of nitrate and ferric ion, owing to the photodegradation of DOM by redundant hydroxyl radical. All of these results suggest that EEMs-PARAFAC is an effective and sensitive analytical technique for evaluating DOM photoreleased from suspended lake sediments and previous studies may underestimate photochemical release of DOM from sediments due to the overlook of the subsequently photodegradation of these released DOM. Thus, the photochemical release of DOM and its associated pollutants from suspended particles in shallow and eutrophic lakes should be more significant then should be paid more attention.


Assuntos
Modelos Químicos , Análise Fatorial , Fluorescência , Substâncias Húmicas/análise , Lagos/química , Nitratos/análise , Processos Fotoquímicos , Fotólise , Espectrometria de Fluorescência , Luz Solar
4.
Water Res ; 181: 115928, 2020 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-32504908

RESUMO

The development of technologically advanced recirculation aquaculture systems (RAS) implies the reuse of water in a high recirculation rate (>90%). One of the most important phases for water management in RAS involves water disinfection in order to avoid proliferation of potential pathogens and related fish diseases. Accordingly, different approaches have been assessed in this study by performing a comparison of photolytic (UV-LEDs) at different wavelengths (λ = 262, 268 and 262 + 268 nm), photochemical (UV-LEDs/H2O2, UV-LEDs/HSO5- and UV-LEDs/S2O82-) and photocatalytic (TiO2/SiO2/UV-LEDs and ZnO/SiO2/UV-LEDs) processes for the disinfection of water in RAS streams. Different laboratory tests were performed in batch scale with real RAS stream water and naturally occurring bacteria (Aeromonas hydrophyla and Citrobacter gillenii) as target microorganisms. Regarding photolytic processes, higher inactivation rates were obtained by combining λ262+268 in front of single wavelengths. Photochemical processes showed higher efficiencies by comparison with a single UV-C process, especially at 10 mg L-1 of initial oxidant dose. The inactivation kinetic rate constant was improved in the range of 15-38%, with major efficiency for UV/H2O2 âˆ¼ UV/HSO5- > UV/S2O82-. According to photocatalytic tests, higher efficiencies were obtained by improving the inactivation kinetic rate constant up to 55% in comparison with a single UV-C process. Preliminary cost estimation was conducted for all tested disinfection methods. Those results suggest the potential application of UV-LEDs as promoter of different photochemical and photocatalytic processes, which are able to enhance disinfection in particular cases, such as the aquaculture industry.


Assuntos
Desinfecção , Purificação da Água , Aquicultura , Peróxido de Hidrogênio , Processos Fotoquímicos , Rios , Dióxido de Silício , Raios Ultravioleta
5.
Proc Natl Acad Sci U S A ; 117(24): 13339-13349, 2020 06 16.
Artigo em Inglês | MEDLINE | ID: mdl-32482882

RESUMO

The ability to modulate cellular electrophysiology is fundamental to the investigation of development, function, and disease. Currently, there is a need for remote, nongenetic, light-induced control of cellular activity in two-dimensional (2D) and three-dimensional (3D) platforms. Here, we report a breakthrough hybrid nanomaterial for remote, nongenetic, photothermal stimulation of 2D and 3D neural cellular systems. We combine one-dimensional (1D) nanowires (NWs) and 2D graphene flakes grown out-of-plane for highly controlled photothermal stimulation at subcellular precision without the need for genetic modification, with laser energies lower than a hundred nanojoules, one to two orders of magnitude lower than Au-, C-, and Si-based nanomaterials. Photothermal stimulation using NW-templated 3D fuzzy graphene (NT-3DFG) is flexible due to its broadband absorption and does not generate cellular stress. Therefore, it serves as a powerful toolset for studies of cell signaling within and between tissues and can enable therapeutic interventions.


Assuntos
Grafite/química , Nanoestruturas/química , Neurônios/efeitos da radiação , Animais , Técnicas Eletroquímicas , Lasers , Nanofios/química , Neurônios/fisiologia , Processos Fotoquímicos , Ratos , Esferoides Celulares/fisiologia , Esferoides Celulares/efeitos da radiação
6.
Nature ; 584(7819): 69-74, 2020 08.
Artigo em Inglês | MEDLINE | ID: mdl-32512577

RESUMO

Enzymes are increasingly explored for use in asymmetric synthesis1-3, but their applications are generally limited by the reactions available to naturally occurring enzymes. Recently, interest in photocatalysis4 has spurred the discovery of novel reactivity from known enzymes5. However, so far photoinduced enzymatic catalysis6 has not been used for the cross-coupling of two molecules. For example, the intermolecular coupling of alkenes with α-halo carbonyl compounds through a visible-light-induced radical hydroalkylation, which could provide access to important γ-chiral carbonyl compounds, has not yet been achieved by enzymes. The major challenges are the inherent poor photoreactivity of enzymes and the difficulty in achieving stereochemical control of the remote prochiral radical intermediate7. Here we report a visible-light-induced intermolecular radical hydroalkylation of terminal alkenes that does not occur naturally, catalysed by an 'ene' reductase using readily available α-halo carbonyl compounds as reactants. This method provides an efficient approach to the synthesis of various carbonyl compounds bearing a γ-stereocentre with excellent yields and enantioselectivities (up to 99 per cent yield with 99 per cent enantiomeric excess), which otherwise are difficult to access using chemocatalysis. Mechanistic studies suggest that the formation of the complex of the substrates (α-halo carbonyl compounds) and the 'ene' reductase triggers the enantioselective photoinduced radical reaction. Our work further expands the reactivity repertoire of biocatalytic, synthetically useful asymmetric transformations by the merger of photocatalysis and enzyme catalysis.


Assuntos
Alcenos/química , Alcenos/metabolismo , Hidrogênio/química , Hidrogênio/metabolismo , Luz , Oxirredutases/metabolismo , Processos Fotoquímicos/efeitos da radiação , Álcoois/química , Álcoois/metabolismo , Alquilação/efeitos da radiação , Biocatálise/efeitos da radiação , Biomassa , Carboxiliases/metabolismo , Flavinas/metabolismo , Modelos Químicos , Modelos Moleculares , Estereoisomerismo
7.
Chemosphere ; 257: 127210, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32502738

RESUMO

BiOI nanosheets have been successfully deposited on the porous Bi2O3 nanorobs via a one-pot precipitation method. The physicochemical features of the as-prepared materials were characterized in detail by a series of techniques, and the results revealed that BiOI nanosheets were evenly distributed on the porous Bi2O3 nanorobs. Because of higher photogenerated electron-hole pairs separation efficiency and the larger specific surface area compared to the pristine Bi2O3 and BiOI, the 50%Bi2O3/BiOI composite exhibited significantly enhanced photocatalytic activity for Cr(VI) reduction under visible light irradiation, and the reduction rate constant was 0.02002 min-1, which was about 27.4 and 2.6 times higher than that of pure Bi2O3 (0.00073 min-1) and BiOI (0.00769 min-1), respectively. Moreover, the 50%Bi2O3/BiOI composite also possessed the excellent photochemical stability and recyclability, thereby facilitating its wastewater treatment application.


Assuntos
Bismuto/química , Cromo/química , Catálise , Cor , Luz , Processos Fotoquímicos
8.
PLoS One ; 15(5): e0232184, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32369508

RESUMO

The ternary chalcogenide Cu3VSe4 (CVSe) with sulvanite structure has been theoretically predicted to be a promising candidate for photovoltaic applications due to its suitable bandgap for solar absorption and the relatively earth-abundant elements in its composition. To realize the absorber layer via an inexpensive route, printed thin-films could be fabricated from dispersions of nano-sized Cu3VSe4 precursors. Herein, cubic Cu3VSe4 nanocrystals were successfully synthesized via a hot-injection method. Similar with reported Cu3VS4 nanocrystals, Cu3VSe4 nanocrystals with cubic structure exhibit three absorption bands in the UV-Visible range indicative of a potential intermediate bandgap existence. A thin film fabricated by depositing the nanoparticles Cu3VSe4 on FTO coated glass substrate, exhibited a p-type behavior and a photocurrent of ~ 4 µA/cm2 when measured in an electrochemical cell setting. This first demonstration of photocurrent exhibited by a CVSe nanocrystals thin film signifies a promising potential in photovoltaic applications.


Assuntos
Nanopartículas/química , Compostos de Selênio/química , Compostos de Selênio/síntese química , Técnicas Eletroquímicas , Nanopartículas/ultraestrutura , Tamanho da Partícula , Processos Fotoquímicos , Semicondutores
9.
Nat Commun ; 11(1): 2600, 2020 05 25.
Artigo em Inglês | MEDLINE | ID: mdl-32451409

RESUMO

Light-dependent or light-stimulated catalysis provides a multitude of perspectives for implementation in technological or biomedical applications. Despite substantial progress made in the field of photobiocatalysis, the number of usable light-responsive enzymes is still very limited. Flavoproteins have exceptional potential for photocatalytic applications because the name-giving cofactor intrinsically features light-dependent reactivity, undergoing photoreduction with a variety of organic electron donors. However, in the vast majority of these enzymes, photoreactivity of the enzyme-bound flavin is limited or even suppressed. Here, we present a flavoprotein monooxygenase in which catalytic activity is controllable by blue light illumination. The reaction depends on the presence of nicotinamide nucleotide-type electron donors, which do not support the reaction in the absence of light. Employing various experimental approaches, we demonstrate that catalysis depends on a protein-mediated photoreduction of the flavin cofactor, which proceeds via a radical mechanism and a transient semiquinone intermediate.


Assuntos
Proteínas de Bactérias/metabolismo , Transporte de Elétrons , Flavina-Adenina Dinucleotídeo/metabolismo , Oxigenases de Função Mista/metabolismo , NAD/metabolismo , Pseudomonas aeruginosa/metabolismo , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Biocatálise , Cristalografia por Raios X , Flavoproteínas Transferidoras de Elétrons/química , Flavoproteínas Transferidoras de Elétrons/genética , Flavoproteínas Transferidoras de Elétrons/metabolismo , Luz , Oxigenases de Função Mista/química , Oxigenases de Função Mista/genética , Modelos Moleculares , NADP/metabolismo , Oxirredução , Processos Fotoquímicos , Pseudomonas aeruginosa/genética
10.
Environ Pollut ; 262: 114360, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32443206

RESUMO

Kütahya city, a thermal power plant (TPPs) affected region of Turkey, has serious air quality problems like similar industrial regions of the world due to the emissions from three closely-located coal-fired TPPs, residential coal combustion along with the contribution of several industrial stacks. The organic chemical speciation of ambient size-segregated particulate matter (PM) was investigated during two seasons at two sites with different pollution characteristics (urban and rural). The ambient PM was collected using a high volume cascade impactor, with 6 stages: PM>10.2, PM10.2-4.2, PM4.2-2.1, PM2.1-1.3, PM1.3-0.69 and PM<0.69. Collected PM samples were extracted with organic solvents and the organic composition (Polycyclic aromatic hydrocarbons (PAHs), n-alkanes and carboxylic acids) was determined by GC-MS. Sources of the organic species were assessed using molecular PAH diagnostic ratios, carbon preference index and wax percentages. More than 70% of the PM-bound PAHs were quantified in submicron particles. Similarly, 34-42% of n-alkanes and approximately 30% of the carboxylic acids were found on the smallest particles. The main sources of the PM-bound organic species were considered as the anthropogenic emissions such as coal and biomass combustion and also vehicular emissions rather than the biogenic sources. Considerably high cancer risk levels were obtained through inhalation of PAHs. Seasonal variations and size distributions of the carboxylic acids and levoglucosan were also evaluated. Polar organic compound concentrations were higher in the summer period at both locations probably due to the higher sunlight intensity and temperature favoring their photochemical formation.


Assuntos
Poluentes Atmosféricos/análise , Hidrocarbonetos Policíclicos Aromáticos/análise , Cidades , Monitoramento Ambiental , Compostos Orgânicos/análise , Tamanho da Partícula , Material Particulado/análise , Processos Fotoquímicos , Centrais Elétricas , Estações do Ano , Turquia
11.
Chemosphere ; 256: 127143, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32473469

RESUMO

In this study, preparation of a nylon film-TiO2 composite sheet with both physical durability under UV irradiation and TiO2 photocatalysis functionality was investigated. First, a nylon film was directly prepared on paper by interfacial polymerization using ethylenediamine and terephthaloyl chloride in a cyclohexane-chloroform mixture (3:1, v/v). Next, the nylon-coated paper was treated with tetraethyl orthosilicate and 3-aminopropyltrimethoxysilane to prepare polysiloxane on its surface. This was followed by fixation of TiO2 powder via electrostatic interactions with the polysiloxane. Although nylon films on paper usually decompose under TiO2 photocatalysis, the nylon film-TiO2 composite sheets prepared using 0.5%-1.0% (w/v) TiO2 did not decompose under photocatalysis. The residual rate of strength of the sheet remained at almost 100% after 240 h, which could be attributed to protection of the sheet by the polysiloxane layer. The nylon film was fibrous and could effectively adsorb acetaldehyde gas. All of the nylon film-TiO2 composite sheets prepared using 0.5%-5.0% TiO2 photocatalytically removed acetaldehyde under UV irradiation and no acetaldehyde gas was detected after 240-300 min. These results show the nylon film-TiO2 composite sheet can effectively remove acetaldehyde gas by photocatalysis and adsorption and could be applied to removal of volatile organic compounds in indoor air.


Assuntos
Acetaldeído/análise , Poluição do Ar em Ambientes Fechados/análise , Nylons/química , Processos Fotoquímicos , Compostos Orgânicos Voláteis/análise , Adsorção , Catálise , Polimerização , Siloxanas/química , Eletricidade Estática , Titânio/química , Raios Ultravioleta
12.
Sci Total Environ ; 732: 138963, 2020 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-32428768

RESUMO

In this paper, a new interface design strategy for bio­carbon/SnS2 nanosheets equipped with CSnS bonds was proposed by using biomass as a template for the efficient photocatalytic conversion of As(III). The characterization results illustrated that the CSnS bonds could effectively prevent the agglomeration of SnS2, expand the photoresponse range and improve the hydrophilicity of the bio­carbon/SnS2 composites while reducing their transfer resistance. Therefore, the construction of CSnS bonds could more efficiently promote the photoredox catalysis of As(III) to As(V) compared with pure SnS2, attributing to the polarization and conjugation effects of the CSn bonds. Meanwhile, CaSO4·nH2O (n = 0, 0.5, 2) could rapidly convert AsO43- into Ca3(AsO4)2 precipitates to eliminate arsenic from the aqueous solution in one step. In particular, 7500 µg/L As(III) could not only be photocatalyzed into As(V) but also be converted to Ca3(AsO4)2 to achieve the removal of arsenic within only 55 min in the coexistence of CaSO4. In addition, the electron transfer path in the photocatalytic oxidation system on arsenite was proposed according to the Mott-Schottky (MS) plots of SnS2 and graphitic carbon. The electron paramagnetic resonance (EPR) results implied that O2- and h+ were the main active substances in the photooxidation arsenic system and the effect of OH could be negligible. Thus, the possible mechanism of the photocatalytic conversion of As(III) was discussed.


Assuntos
Biomassa , Arseniatos , Compostos de Cálcio , Carbono , Catálise , Oxirredução , Processos Fotoquímicos , Enxofre , Estanho
13.
Chemosphere ; 255: 126878, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32387727

RESUMO

Cobalt (Co) co-doped TiO2 photo-catalysis were synthesized, characterized and tested toward solar photocatalytic oxidation of toluene (TOL). A multi-technique approach was used to characterize and relate the photo-catalytic property to photo-oxidation performance. Adding Co to TiO2 significantly changed crystal size and surface morphology (surface area, pore-volume, and pore size), reduced the bandgap energy of TiO2 and improved the solar photo-oxidation of TOL. Up to 96.5% of TOL conversion (%TNconv) was achieved by using Co-TiO2 compared with 28.5% with naked TiO2. The maximum %TNconv was achieved at high hydraulic retention time (HRT) ≥ 100 s, Co content in the photo-catalyst of 5 wt% and relative humidity (%RH) of 50%. The mechanism of TOL solar oxidation was related to the concentration of OH• and •O2-. radicals produced from the generated electrons and holes on the surface of Co-TiO2. The products formed during the photo-catalytic oxidation of TOL were mainly CO2 and water, and minor concentration of benzene and benzaldehyde. Overall, the Co-TiO2 could be used as a potential photo-catalyst for the oxidation of toluene in gas-phase streams on an industrial scale.


Assuntos
Cobalto/química , Tolueno/química , Benzeno/química , Catálise , Oxirredução , Processos Fotoquímicos , Luz Solar , Titânio/química
14.
Plant Physiol Biochem ; 151: 589-600, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32330839

RESUMO

Cannabis sativa L is an important plant, which is a source of durable fibers, nutritious seeds, and medicinally important phytocannabinoids including Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD). Light has shown to be a key modulator of biomass and cannabinoid yield suggesting responsive photochemical machinery. The present study was envisaged to understand the effect of the increasing levels of metabolic THC on the photochemical efficiency in Cannabis. The chlorophyll a fluorescence kinetics, photosynthetic pigments and immuno-detection of the photosynthetic machinery was analyzed on seven accessions from different environments, in conjunction with the cannabinoid content. All the accessions were clearly divided into three groups based on their relative content of CBD and THC. Group I with (CBD/THC > 1) had a clear advantage in terms of the damage to the D1, RbCL and Lhc1 protein holo-complex. Performance indicators of photochemistry based on the OJIP kinetics suggested a stoichiometrically negative correlation with the THC content. Zeaxanthin-dependent quenching is primarily responsible for lower NPQ in Group III with high THC content (THC > 6%). The THC treatment on Arabidopsis thaliana also suggested dose-dependent decrease in the photochemical efficiency suggesting the exclusivity of THC in causing the response. This resulted in the damage of photosynthetic machinery and the generation of free radicals, thereby compromising the yield. The study also opens a new screening method for Cannabis, based on cannabinoid content.


Assuntos
Cannabis , Dronabinol , Processos Fotoquímicos , Cannabis/química , Cannabis/fisiologia , Dronabinol/metabolismo
15.
Chemosphere ; 253: 126660, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32272309

RESUMO

Recently, a set of graph-based tools have been introduced for the identification of singular events of O3, NO2 and temperature time series, as well as description of their dynamics. These are based on the use of the Visibility Graphs (VG). In this work, an improvement of the original approach is proposed, being called Upside-Down Visibility Graph (UDVG). It adds the possibility of investigating the singular lowest episodes, instead of the highest. Results confirm the applicability of the new method for describing the multifractal nature of the underlying O3, NO2, and temperature. Asymmetries in the NO2 degree distribution are observed, possibly due to the interaction with different chemicals. Furthermore, a comparison of VG and UDVG has been performed and the outcomes show that they describe opposite subsets of the time series (low and high values) as expected. The combination of the results from the two networks is proposed and evaluated, with the aim of obtaining all the information at once. It turns out to be a more complete tool for singularity detection in photochemical time series, which could be a valuable asset for future research.


Assuntos
Poluentes Atmosféricos/análise , Monitoramento Ambiental/métodos , Processos Fotoquímicos , Smog
16.
Nat Commun ; 11(1): 1956, 2020 04 23.
Artigo em Inglês | MEDLINE | ID: mdl-32327665

RESUMO

The dehydrogenative alkenylation of C-H bonds with alkenes represents an atom- and step-economical approach for olefin synthesis and molecular editing. Site-selective alkenylation of alkanes and aldehydes with the C-H substrate as the limiting reagent holds significant synthetic value. We herein report a photocatalytic method for the direct alkenylation of alkanes and aldehydes with aryl alkenes in the absence of any external oxidant. A diverse range of commodity feedstocks and pharmaceutical compounds are smoothly alkenylated in useful yields with the C-H partner as the limiting reagent. The late-stage alkenylation of complex molecules occurs with high levels of site selectivity for sterically accessible and electron-rich C-H bonds. This strategy relies on the synergistic combination of direct hydrogen atom transfer photocatalysis with cobaloxime-mediated hydrogen-evolution cross-coupling, which promises to inspire additional perspectives for selective C-H functionalizations in a green manner.


Assuntos
Aldeídos/química , Alcanos/química , Alcenos/química , Alcenos/síntese química , Catálise , Técnicas de Química Sintética , Química Verde , Estrutura Molecular , Compostos Organometálicos/química , Processos Fotoquímicos , Estereoisomerismo
17.
Chemosphere ; 254: 126671, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32334243

RESUMO

Efficient elimination of U(VI) from uranium wastewater is an urgent task for sustainable nuclear energy and environmental protection. In this study, magnetic graphene oxide decorated graphitic carbon nitride (mGO/g-C3N4) nanocomposite was prepared and used for photocatalytic reduction of U(VI) in wastewater under visible LED light irradiation for the first time. The batch experiments indicated that the mGO/g-C3N4 (mGCN) nanocomposite could efficiently reduce U(VI) under visible LED light, and a high U(VI) extraction capacity of 2880.6 mg/g was obtained with an extraction efficiency of 96.02%. The transmission electron microscopy (TEM) elemental mapping, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analyses demonstrated that the soluble U(VI) was immobilized by transforming it to metastudtite ((UO2)O2·2H2O) by mGCN nanocomposite under visible LED light irradiation. This work indicated that the mGCN is a promising visible light catalyst for treatment of uranium wastewater.


Assuntos
Processos Fotoquímicos , Urânio/química , Poluentes Radioativos da Água/química , Catálise , Grafite , Luz , Óxido de Magnésio , Nanocompostos/química , Compostos de Nitrogênio , Águas Residuárias/química
18.
Chemosphere ; 254: 126796, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32335441

RESUMO

Chlorine-containing organic compounds were discharged informally as a result of untreated industrial wastewater, which caused groundwater pollution. In this study, titanium dioxide nanotube arrays (TNAs) were modified with copper oxide to photoelectrochemical (PEC) active persulfate to degrade trichloroethylene (TCE). The SEM results show copper nano-particles with a cubic shape were successfully deposited on the surface of TNAs. The results of UV-vis analysis indicate the absorption wavelengths red-shift to 550-600 nm for better light utilization. CuO/TNAs were dominated by the anatase phase after sintering at 450 °C with significant visible light response. The chemical contents for the surface of CuO/TNAs are 23.7, 53.4, 18.4 and 4.4% for C, O, Ti and Cu, respectively. The photocurrent of CuO/TNAs is 1.89 times higher than that of TNAs-93 cm^2-1hr under 100 W Hg-lamp illuminations. This demonstrates the efficiency of light utilization of TNAs was improved by the modification with copper nanoparticles. The degradation rate of TCE in the anodic chamber is more effective than that in the cathodic chamber because of the synergistic effect of hydroxyl and sulfate radicals. The mechanism of TCE degradation via persulfate in the PEC system was proposed and discussed in detail.


Assuntos
Processos Fotoquímicos , Sulfatos/química , Tricloroetileno/química , Cobre , Eletrodos , Água Subterrânea , Nanotubos/química , Titânio , Águas Residuárias
19.
Environ Sci Technol ; 54(8): 4903-4911, 2020 04 21.
Artigo em Inglês | MEDLINE | ID: mdl-32227921

RESUMO

Dissolved black carbon (DBC) is an important component of dissolved organic matter pool; however, its photochemical properties are not fully understood. In this study, we determined the excited triplet-state quantum yields of DBC (3DBC*) and 1O2 quantum yields (Φ1O2) of six diverse DBCs using sorbic alcohol, 2,4,6-trimethylphenol (TMP), and furfuryl alcohol and compared the results with quantum yields of reference natural organic matters (NOMs). The average Φ1O2 of six DBCs (4.2 ± 1.5%) was greater than that of terrestrial NOM (2.4 ± 0.3%) and comparable to autochthonous NOM (5.3 ± 0.2%). Using TMP as a probe for oxidizing triplets, DBC presented significantly higher apparent quantum yield coefficients for degrading TMP (fTMP) than the reference NOM, reflecting that the fTMP values of low-energy 3DBC* were approximately 12-fold greater than those of low-energy 3NOM*. The differences in the fTMP and Φ1O2 trends among the DBCs indicated that the 3DBC* responsible for these reactions may be from different sources. In addition, DBC was much more effective than NOM, on a carbon-normalized basis, during photodegradation of pharmaceutically active compounds. This result confirms that the presence of DBC can accelerate the photodegradation of contaminants that are susceptible to one-electron oxidation by triplets.


Assuntos
Processos Fotoquímicos , Fuligem , Carbono , Fotoquímica , Espécies Reativas de Oxigênio
20.
Chemosphere ; 253: 126655, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32302899

RESUMO

The degradation kinetics and mechanisms of Rhodamine B (RhB) dye by •OH and SO4•- based advanced oxidation processes were investigated. The •OH and SO4•- radicals were generated by UV photolysis of hydrogen peroxide and persulfate (i.e., UV/H2O2 and UV/PS), respectively. The effects of initial solution pH, RhB concentration, oxidant dosage, Fe2+ concentration, and water matrices were examined. The results showed that the degradation of RhB followed pseudo-first-order kinetics in both processes, with the UV/H2O2 process exhibiting better performance than that of the UV/PS process. Acidic conditions were favorable to the degradation of RhB in both systems. Increasing the oxidant dosage or decreasing the contaminant concentration could enhance the degradation of RhB. Photo-Fenton-like processes accelerated the performance when Fe2+ was added into both systems. The removal efficiency of RhB was inhibited upon the addition of humic substances. The addition of Cl- displayed no significant effect and promoted RhB degradation in UV/H2O2 and UV/PS systems, respectively. The presence of NO3- promoted RhB degradation, while H2PO4- and C2O42- showed an inhibitory effect on both UV/H2O2 and UV/PS processes. Radical scavenging tests revealed the dominant role of SO4•- radicals in the UV/PS system. Furthermore, the evolution of low molecular weight organic acids and NH4+ during the degradation of RhB in these two processes were compared. Both UV/H2O2 and UV/PS systems led to similar formation trends of NH4+ and some ring-opening products (e.g., formic acid, acetic acid, and oxalic acid), suggesting some analogies in the decay pathways of RhB by •OH and SO4•--induced oxidation processes.


Assuntos
Rodaminas/química , Poluentes Químicos da Água/química , Substâncias Húmicas , Peróxido de Hidrogênio/química , Radical Hidroxila/química , Cinética , Compostos Orgânicos , Oxirredução , Processos Fotoquímicos , Fotólise , Sulfatos/química , Raios Ultravioleta , Poluentes Químicos da Água/análise
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