Photochemical reaction of tricresyl phosphate (TCP) in aqueous solution: Influencing factors and photolysis products
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Hydroxyl radical
Photodegradation
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The photodegradation of pesticides was investigated on adsorbed phases: silica, kaolin, bentonite and on a standard soil. Kinetic results show that the photodegradation of phenmedipham is dependant on the nature of the support. On silica and bentonite the degradation is immediate while the photodegradation is slow on kaolin and standard soil. Also, the nature of the photodegradation depends on the reactional mechanism on the support.
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Photodegradation of Polycyclic Aromatic Hydrocarbons (PAHs) is a main environmental behavior and plays an important role in the fate of PAHs in environment.In order to understand the photodegradation law of Polycyclic Aromatic Hydrocarbons(PAHs)in soil, aeolian sand in blow-sand region of Northern Shaanxi was chosen as typical soil and phenanthrene (Phe) as typical pollutant of PAHs.Photodegradation law of Phe on soil surface was simulated.In addition, effects of initial Phe concentration, light intensity, time and pH on photodegradation of Phe in aeolian sand was assessed.Results show that the photodegradation of Phe followed pseudo first-order kinetics.Photodegradation rate constant of Phe increased with the increasing of irradiation intensity which the order was as followed: 125W>100W>75W>50W.Irradiation intensity enhances photodegradation of PAHs on soil surfaces.Photodegradation half-life of Phe ranged from 2.474 hours to 3.095 hours under different irradiation intensity.Degradation rate increases as pH increase and photodegradation is more rapid in alkaline medium.Photodegradation rate is the lowest as initial concentration is the largest.
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An investigation was conducted to measure the rates of photodegradation of thifensulfuron-methyl in Millipore and Saskatchewan natural waters (Difenbaker Lake, Candle Lake, Saskatchewan River) using 254 nm irradiation. The primary degradation was found to follow pseudo-first-order kinetics. The rate constants determined for Difenbaker Lake, Candle Lake, Saskatchewan River and Millipore water were 9.94, 8.68, 9.00 and 8.55×10−5 (s−1), respectively. There was no significant difference in the photodegradation rates for both natural and Millipore waters. The quantum yields in these waters were 0.0135, 0.0167, 0.0215 and 0.0148, respectively. The photodegradation rate constant was enhanced relative to neutral waters (pH=7; 0.366×10−4 (s−1)) for strongly acidic (pH=2.7) or alkaline environments (pH=11.3) with rate constants of 1.65 and 1.69×10−4 (s−1) respectively. Degradation was also enhanced when either Fe3+ or H2O2 were added to the system, with rate constants of 1.24 (Fe3+) and 1.12×10−4 (s−1) (H2O2). In view of the rapid rates observed in these laboratory studies, it is proposed that photodegradation will likely be a major pathway for degradation of thifensulfuron-methyl in Saskatchewan natural waters.
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Absolute rate constants and degradation efficiencies for hydroxyl radical and hydrated electron reactions with four different sulfa drugs in water have been evaluated using a combination of electron pulse radiolysis/absorption spectroscopy and steady-state radiolysis/high-performance liquid chromatography measurements. For sulfamethazine, sulfamethizole, sulfamethoxazole, and sulfamerazine, absolute rate constants for hydroxyl radical oxidation were determined as (8.3 +/- 0.8) x 10(9), (7.9 +/- 0.4) x 10(9), (8.5 +/- 0.3) x 10(9), and (7.8 +/- 0.3) x 10(9) M(-1) s(-1), respectively, with corresponding degradation efficiencies of 36% +/- 6%, 46% +/- 8%, 53% +/- 8%, and 35% +/- 5%. The reduction of these four compounds by their reaction with the hydrated electron occurred with rate constants of (2.4 +/- 0.1) x 10(10), (2.0 +/- 0.1) x 10(10), (1.0 +/- 0.03) x 10(10), and (2.0 +/- 0.1) x 10(10) M(-1) s(-1), respectively, with efficiencies of 0.5% +/- 4%, 61% +/- 9%, 71% +/- 10%, and 19% +/- 5%. We propose that hydroxyl radical adds predominantly to the sulfanilic acid ring of the different sulfa drugs based on similar hydroxyl radical rate constants and transient absorption spectra. In contrast, the variation in the rate constants for hydrated electrons with the sulfa drugs suggests the reaction occurs at different reaction sites, likely the different heterocyclic rings. The results of this study provide fundamental mechanistic parameters, hydroxyl radical and hydrated electron rate constants, and degradation efficiencies that are critical for the evaluation and implementation of advanced oxidation processes (AOPs).
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Using agarose gel electrophoresis, we have measured the yield of single-strand breaks (SSBs) induced by 137Cs gamma irradiation in a variety of plasmid DNA substrates ranging in size from 2.7 kb to 38 kb irradiated in aerobic aqueous solution in the presence of the hydroxyl radical scavenger dimethyl sulfoxide (DMSO). Under these conditions DNA SSBs are caused mainly by the hydroxyl radical. Using the competition between DMSO and DNA for the hydroxyl radical, we have estimated the rate coefficient for the reaction of the hydroxyl radical with DNA. The results cannot be characterized by conventional steady-state competition kinetics. However, it is possible to describe the second-order rate constant for the reaction as a function of the scavenging capacity of the solution. The second-order rate constant increases with increasing scavenging capacity, rising from about 5 x 10(8) dm3 mol-1 s-1 at 10(5) s-1 to about 10(10) dm3 mol-1 s-1 at 10(10) s-1. This dependence of the second-order rate constant on the scavenging capacity appears to be more pronounced for larger plasmids.
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Polycyclic aromatic hydrocarbons (PAHs) are a group of major contaminants that are ubiquitous in the environment due to their toxicity, mutagenicity and carcinogenicity. This paper studied the soil borne PAHs photodegradation under UV irradiation with phenanthrene(Phe) as target contaminants. The effects of temperature,humic acids(HA)and the intensity of UV irradiation on the Phe photodegradation were investigated. The dynamics of photodegradation of Phe were studied under different conditions. The results show that the rate of Phe photodegradation increases when the temperature rises from 20 ℃ to 30 ℃. The HA played a sensitivizing role during the Phe photodegradation. When the HA concentration was 5 mg·kg-1, HA could efficiently sensitivize the Phe photodegradation. The rate of photodegradation decreases with the decreasing UV irradiation intensity, correlated positively. The half-life increases with the decreasing UV irradiation intensity, correlated negatively.
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The photodegradation of pesticides was investigated on adsorbed phases: silica, kaolin, bentonite and on a standard soil. Kinetic results show that the photodegradation of phenmedipham is dependant on the nature of the support. On silica and bentonite the degradation is immediate while the photodegradation is slow on kaolin and standard soil. Also, the nature of the photodegradation depends on the reactional mechanism on the support.
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Abstract Enhancement of the photodegradation of bisphenol A (BPA) by β‐cyclodextrin (β‐CD) was investigated under a 30 W UV disinfection lamp (λ max = 254 nm). The photodegradation rate of BPA in aqueous solutions with β‐CD was faster than that in aqueous solutions without β‐CD; for example, after 50 min of UV irradiation, β‐CD had increased the photodegradation efficiency by about 46.5% for 10 mg dm −3 BPA. The photodegradation of 2.5–20 mg dm −3 BPA in aqueous solutions was found to follow pseudo‐first‐order kinetics. The first‐order rate constant showed a 12‐fold increase in the presence of β‐CD. Factors such as β‐CD concentration, pH, BPA initial concentration and organic solvent influencing the photodegradation of BPA were studied and are described in detail. Variations in the pH and electrical conductivity of solutions were observed during the photodegradation process. The enhancement of photodegradation of BPA results mainly from the lower bond energy between some atoms in the BPA molecule after inclusion interaction with β‐CD. Copyright © 2006 Society of Chemical Industry
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