共查询到20条相似文献,搜索用时 31 毫秒
1.
Laura A. Peña Alissa M. Chan Larissa R. Cohen Karen Hou Brent M. Harvey Patrick E. Hoggard 《Photochemistry and photobiology》2014,90(4):760-766
Unactivated MCM‐41 mesoporous silica catalyzes the photodecomposition of chloroform to phosgene and hydrogen chloride under near‐UV (λ > 360 nm) irradiation. The rate of photodecomposition increases toward an asymptotic limit as the O2 partial pressure is increased. Deuterochloroform does not decompose under the same experimental conditions. Low concentrations of both cyclohexane and ethanol quench the photodecomposition, whereas water, up to its solubility limit, does not. Dissolved tetraalkylammonium salts suppress photodecomposition. The data are consistent with a mechanism in which light absorption by an SiO2 defect yields an electron‐deficient oxygen atom, which then abstracts hydrogen from chloroform. The resulting CCl3 radicals react with oxygen to form a peroxy radical that decomposes, eventually yielding phosgene and hydrogen chloride. 相似文献
2.
Infrared study of UV-irradiated tungsten trioxide powders containing adsorbed dimethyl methyl phosphonate and trimethyl phosphate 总被引:1,自引:0,他引:1
Anil Waghe Sofian M. Kanan Imad Abu-Yousef Bruce Jensen Carl P. Tripp 《Research on Chemical Intermediates》2006,32(7):613-623
The photodecomposition of dimethyl methylphosphonate (DMMP) and trimethyl phosphate (TMP) adsorbed on monoclinic WO3 powders when irradiated by ultraviolet light (UV) in air, oxygen, and under evacuation was investigated using infrared spectroscopy
(IR). The IR spectra show that DMMP decomposes into methyl phosphonate upon exposure to 254 nm UV for 2 h at room temperature
in air. The same decomposition of DMMP occurs only at temperatures above 300°C without UV illumination. TMP differs from DMMP
in that the photodecomposition product is not the same as the decomposition product obtained by heating above 300°C. Thermal
decomposition leads to formation of a phosphate on the surface, whereas photodecomposition leads to the same adsorbed methyl
phosphonate as found for the thermal or photodecomposition of DMMP. Since TMP does not contain a P-CH3 bond, the formation of a methyl phosphonate on the surface after UV illumination involves a mechanism where CH3 groups migrate from the methoxy group to the phosphorous central atom. No decomposition is observed at room temperature when
DMMP or TMP adsorbed on WO3 is irradiated under vacuum or in nitrogen atmosphere. Therefore, the photodecomposition of either DMMP or TMP adsorbed on
WO3 at room temperature does not involve a reaction with the lattice oxygen but rather a reaction with the oxygen radicals produced
by the decomposition of ozone. 相似文献
3.
L. Wojnárovits L. H. Luthjens H. C. De Leng A. Hummel 《Journal of Radioanalytical and Nuclear Chemistry》1986,101(2):349-357
Results of photodecomposition studies of liquid cyclohexane n-octane, n-decane and methylcyclohexane with 7.6 eV photons are reported for various temperatures. In all cases the yield of molecular elimination decreases with decreasing temperature. In the presence of xenon this yield is also found to decrease. The fluorescence decay rate of cyclohexane and methylcyclohexane as obtained from pulse radiolysis measurements, shows a considerable temperature dependence, and is increased in the presence of xenon. The results of the photodecomposition experiments and of the fluorescence experiments are compared and discussed. 相似文献
4.
Abstract— The release of orthophosphate from oxygen-saturated aqueous solutions of disodium phenyl phosphate by near-UV and visible light was enhanced in the presence of the sensitizing dyes methylene blue, rose bengal and thionine. The reaction was accompanied by the bleaching of these dyes. In the absence of oxygen, under nitrogen, the photodecomposition was very much slower. In deuterium oxide as the solvent, the dye-sensitized photodecomposition was 9 times faster than in normal water. This result suggests that singlet oxygen is probably the reactive species in the dye-sensitized reaction. 相似文献
5.
6.
Sherin PS Tsentalovich YP Snytnikova OA Sagdeev RZ 《Journal of photochemistry and photobiology. B, Biology》2008,93(3):127-132
Quantum yields of photodecomposition and triplet state formation under aerobic and anaerobic conditions are determined for kynurenine (KN), 3-hydroxykynurenine (3OHKN), xanthurenic acid (XAN), and kynurenine adducts of glutathione (GSH-KN), cysteine (Cys-KN), histidine (His-KN), and lysine (Lys-KN) in aqueous solutions. The highest yields of anaerobic photodecomposition were obtained for GSH-KN and His-KN adducts, which correlates with the highest triplet yields for these compounds. In aerobic conditions, the photodecomposition yields for all compounds under study increase; the highest decomposition rates were observed for His-KN and 3OHKN. The fast decomposition of the latter is attributed to the dark autoxidation of the starting compound. 相似文献
7.
It is found that oxygen accelerates the photodecomposition of poly(vinyl chloride) whereas hydrogen chloride inhibits it. It is postulated that O2 quenches energy-rich polyenes and reacts in the singlet state ultimately yielding carbonyl functions which themselves absorb the radiation and speed up the photodecomposition. The HCl is thought to undergo addition to already formed polyenes thereby reducing the amount of light absorbed and consequently causing retardation. 相似文献
8.
DETERMINATION OF PARAMETERS OF EXCITED STATES OF DNA and RNA BASES BY LASER UV PHOTOLYSIS 总被引:1,自引:0,他引:1
Abstract— The mechanism of photodecomposition of nucleic acid bases in a neutral aqueous solution upon two-step excitation of high-lying electronic states by a powerful laser UV radiation is discussed. Experimental dependences of photodecomposition efficiency versus UV radiation intensity are measured both under picosecond and nanosecond laser UV irradiations. By comparison of experimental dependences with a theoretical model, we obtain some characteristics of excited states, such as lifetime t1 of the first electronic excited state S1 intersystem crossing yield φ, photosensitivity from an intermediate excited state and others for all five nucleic acid bases. 相似文献
9.
S. V. Klement’eva O. G. Mishchenko S. V. Maslennikov I. V. Spirina 《Russian Journal of General Chemistry》2007,77(4):607-610
Kinetic relations holding in photodecomposition of substituted o-benzoquinones were determined, and primary photodecomposition products were identified. Photochemical transformations of o-benzoquinones in saturated hydrocarbons were presumed to follow two pathways: decarbonylation and reduction. The first of these is favored by the presence of electron-donor substituents in the quinoid ring. 相似文献
10.
Ag(I) nanoclusters doped in X and mordenite zeolites were prepared and analyzed using spectroscopy. Both experimental and
theoretical studies of the prepared compounds show the presence of silver nanoclusters with various sizes and environments.
The presence of Ag(I) nanoclusters doped in X and mordenite zeolites with high silver loadings enhanced the photodecomposition
rate of carbofuran 215-and 184-fold, respectively, while the photodecomposition of carbaryl in the presence of these catalysts
show room temperature rate constants that are 182-and 168-times faster than the photodecomposition of carbaryl in the absence
of the silver-doped zeolite catalysts. The reaction rates were found to be dependent on the amount of silver loaded into the
zeolite. 相似文献
11.
采用阳极电化学氧化在铝片表面制备出表面含有氧化铝膜的铝片(AAO/Al), 分别用FTIR-ATR技术和密闭间歇式反应装置考察了该样片对油酸和乙烯的光解作用, 结合UV-DRS和FTIR表征结果对薄膜在油酸和乙烯光解中的作用进行了探讨. 结果表明:AAO/Al能够吸收小于265 nm的紫外光, 而无AAO膜的铝片对波长大于220 nm的紫外光没有任何吸收;254 nm紫外光照射下AAO/Al对油酸和乙烯的光解具有明显的促进作用, 光照3 h油酸的分解率达到70%, 乙烯也有9%的分解, 但相同条件下在无AAO膜的铝片上, 油酸的光解率仅为30%, 乙烯几乎不分解;然而, 在365 nm紫外光照射下, AAO/Al同纯铝片一样对两反应物的光解都没有任何促进作用. 分析认为, AAO膜能吸收254 nm的紫外光和对有机物分解具有光催化作用的可能原因是在AAO膜结构中存在过量的Al原子和氧空位. 相似文献
12.
The submicrometer-sized titania hollow spheres have been synthesized by employing sulfonated polystyrene latex particles as a template in sol-gel method. Photocatalytic activity of the hollow spheres was investigated by focusing on the effect of electron scavengers in the photocatalytic decomposition of methylene blue (MB). Photocatalytic activities of titania hollow spheres were significantly enhanced by the addition of peroxydisulfate as an electron scavenger. The rate constant for photodecomposition of MB was increased more than two times by the addition of peroxydisulfate. The significant increase in the photodecomposition rate seems to be related to electrons scavenging as well as production of additional oxidizing species. It was found that the optimum concentration of peroxydisulfate was 10 mM. Further increase in the concentration of peroxydisulfate is not recommended due to the saturation of reaction rate by the excess amount of SO(4)(2-) species. 相似文献
13.
The solution-phase photodecomposition of l, l-dichloro-2,2-bis(5′-chloro-2′-methoxy-phenyl)ethylene (MPE) has been studied at an excitation wavelength of 313 nm in the presence of O2 as well as in vacuum-degassed solutions. Only two non-volatile compounds are produced: 2,5-dichloro-3-(5′-chloro-2′-methoxyphenyl)benzofuran (BFD) and a minor product which was not identified. The BFD represents approximately 90% of the total non-volatiles. The volatile products were identified as CH3Cl, CH4 and HC1, with CH3C1 being approximately 99.9 % of the total volatiles. Photolyses were carried out in C6H12 and CCI4 solvents, the same products being observed in both solvents. Variation of MPE concentration has little or no effect on the relative quantum yield of decomposition. The photodecomposition of MPE does not follow the same pathway as the photodecomposition of DDE. 相似文献
14.
本文研究了半导体悬浮体系光催化分解有机磷化合物的条件,只有在光照、催化剂和氧同时存在的条件下才能有效地光催化分解有机磷化合物;测量了两种有机磷化合物在各种半导体催化剂上的分解速率,反应速率与催化剂的种类和表面性质有关;对光催化分解马拉硫磷的反应机理进行了初步探讨。 相似文献
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16.
Nishino H Kosaka A Hembury GA Aoki F Miyauchi K Shitomi H Onuki H Inoue Y 《Journal of the American Chemical Society》2002,124(39):11618-11627
The absolute asymmetric photoreaction (AAP) of racemic aliphatic amino acids, such as alanine (Ala) and leucine (Leu), by left- and right-handed circularly polarized light (l- and r-CPL) irradiation was investigated in aqueous solutions at various pHs, by using the Onuki-type polarizing undulator installed in an electron storage ring. The magnitude of the optical purity (op) generated and the enantiomer-enriching mechanism operative in the AAP were found to be entirely dependent on the ionic state (and thus pH) of the amino/carboxylic acid moieties. At pH 1, the op of Ala and Leu determined by circular dichroism (CD) spectral measurement gradually developed with CPL irradiation, according to Kagan's equation. In contrast, irradiation at pH 7 gave op's much smaller than the theoretical values predicted by Kagan's equation. However, it turned out that the photodecomposition at pH 7 produces the corresponding alpha-hydroxycarboxylic acids stereoselectively, the CD sign of which is just opposite to that of the remaining amino acid, thus affording the apparently small op. It is concluded that, irrespective of solution pH, the AAP of amino acid proceeds upon CPL irradiation. At pH 1, the photodecomposition of valine, Leu, and isoleucine occurs via a Norrish type II mechanism, which is also applicable to other amino acids possessing a gamma-hydrogen. In the case of amino acids lacking a gamma-hydrogen, such as glycine and Ala, the photodecomposition mechanism is a photodeamination/hydroxylation and a Norrish type I reaction. At pH 7, the main photoproducts were ammonia and alpha-hydroxycarboxylic acids that were produced via photodeamination. 相似文献
17.
The photostability of nine ferrocene derivatives of varying functionality was investigated using cyclic voltammetry. Derivatives with carbonyl groups (aldehyde or ketone) directly attached to the cyclopentadiene ring system were found to decompose in aqueous (pH 7.4) solution over a period of 10 min when exposed to light. The kinetics of the photodecomposition process were investigated and the relative values of the rate constants for the photodecomposition tabulated. The implications for biosensor applications are assessed. 相似文献
18.
Polypodium leucotomos extract inhibits trans-urocanic acid photoisomerization and photodecomposition
Capote R Alonso-Lebrero JL García F Brieva A Pivel JP González S 《Journal of photochemistry and photobiology. B, Biology》2006,82(3):173-179
In this report, we demonstrate a possible molecular mechanism by which a hydrophilic extract of the leaves of the fern Polypodium leucotomos (Fernblock, PL) blocks ultraviolet (UV)-induced skin photodamage. The extract inhibits UVA and UVB light induced photoisomerization of trans-urocanic acid (t-UCA), a common photoreceptor located in the stratum corneum, and also blocks its photodecomposition in the presence of oxidizing reagents such as H2O2, and titanium dioxide (TiO2). PL protects in vitro human fibroblasts from UV-induced death as well. These results suggest the potential of employing the PL extract as a component of sunscreen moistures in order to prevent photodecomposition of t-UCA, to inhibit UV-induced deleterious effects of TiO2 and to protect skin cells and endogenous molecules directly involved in skin immunosurveillance. 相似文献
19.
Abstract The photodecomposition of 4-dimethylamino-3,5-xylyl-N-methyl carbamate (Zectran) in aerated and degassed solution has been carried out. Three major photoproducts were detected and characterized to be: 4-dirnethylamino-3,5-dimethyl Rhenol, 4-hydroxy-2,6-dimethyl-N-methyl benzamide and 4-monomethylamino-3,5-xylyl-N-methyl carbamate. The phenol and benzamide products suggest that one of the pathways of photodecomposition of Zectran is via a photo-Fries rearrangement. The ortho-benzamide (5-dimethylamino-4,6-dimethyl-2-hydroxy-N-methyl benzamide) which could also be expected to occur in a photo-Fries reaction, was not observed. The excitation wavelength was > 296.7 nm, i.e. radiation available in the solar spectrum. Thus the products observed in this study may be expected to occur in the environment as a result of the action of sunlight on Zectran. 相似文献
20.
I. K. Larin T. I. Belyakova N. A. Messineva A. I. Spasskii E. M. Trofimova 《Kinetics and Catalysis》2011,52(4):513-517
The kinetics of photodecomposition of Halons CF3Br and C2F4Br2 was studied at different times of the irradiation of a mixture of these substances with oxygen at the wavelength λ = 253.7
nm. Kinetic data were obtained from changes in the absorption spectra in the region of Halon absorption and at a wavelength
of 416 nm, which corresponds to the absorption maximum of molecular bromine. Kinetic schemes were proposed for the photodecomposition
of CF3Br and C2F4Br2 at λ = 253.7 nm, and the quantum yields of their photodecomposition at this wavelength were determined. 相似文献