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41.
溶液中阴离子和腐殖酸对UV/H2O2降解2,4-二氯酚的影响 总被引:2,自引:0,他引:2
研究了UV/H2O2工艺对2,4-二氯酚(2,4-DCP)的去除效果和水中阴离子、腐殖酸对该工艺降解2,4-DCP的影响.结果表明:UV/H2O2工艺可以有效地去除水中2,4-DCP,光降解过程符合一级反应动力学模型;在H2O2投加量为8 mg/L、1个30 W低压汞灯照射下,2,4-DCP在蒸馏水和自来水中反应速率常数分别为0.023 2、0.016 2 min-1;NO-3、Cl-、HCO-3对2,4-DCP光降解有抑制作用,当3种阴离子摩尔浓度为0.5、10.0、20.0 mmol/L时,对2,4-DCP光降解的抑制程度为HCO-3>NO-3>Cl-;腐殖酸在低浓度时,促进光降解反应进行,在高浓度时,2,4-DCP的光降解受到抑制.自来水中的反应速率常数低于蒸馏水中的反应速率常数是由于水中多种阴离子和腐殖酸影响的结果. 相似文献
42.
The dye malachite green (MG) is used worldwide as a fungicide in aquaculture. It is a toxic substance which in aqueous solutions is partly converted into its non-ionic colorless form (leucocarbinol). The equilibrium between these two forms is pH-dependent (pK = 6.9). To assess the photodegradation of MG under sunlight conditions, both species were irradiated separately in aqueous solutions with different pH values (4.0 and 12.0) using various ultraviolet and visible wavelength ranges (UV/VIS). A 700 W high-pressure mercury lamp with special filters was used. No artificial photooxidizers such as H2O2 or TiO2 were added. MG leucocarbinol proved to be much more sensitive to irradiation than the dye form. Quantum yields Φ were calculated for some wavelength ranges as follows: MG carbinol: Φ(280-312nm) is 4.3 × 10−3, Φ(313-410nm) is 5.8 × 10−3, and MG dye: Φ(280-312nm) is 4.8 × 10−5, Φ(313-365nm) is 1.1 × 10−5, and Φ(>365nm) is 0, respectively. Therefore, the solar photolysis of MG is an important sink and primarily depends on the photodegradation of the colorless leucocarbinol. During the irradiation of MG leucocarbinol with wavelengths >365 nm, an intermediate was formed which has photocatalytical properties. 相似文献
43.
J. Senthilnathan Ligy Philip 《Journal of environmental science and health. Part. B》2013,48(3):262-270
Lindane (1α, 2α, 3β, 4α, 5α, 6β-hexachloro cyclohexane), methyl parathion (O,O-dimethyl-O-4-nitrophenyl phosphorothioate) and dichlorvos (2,2-dichlorovinyl-O-O-dimethyl phosphate) are removed from water individually and as a mixture by photo degradation using suspended and immobilized forms of TiO2 (Degussa P-25). Studies were conducted to optimize the coating thickness of immobilized photo catalyst. The rate of degradation of pesticides was compared in both suspended and immobilized TiO2 systems. Degradation studies of mixed pesticides were carried out with low concentrations (1.0 and 2.5 mg/L) of pesticides. Only three intermediate byproducts such as methyl paraoxon, O,O,O-trimethyl phosphonic thionate and p-nitrophenol were observed during the methyl parathion degradation in suspended, immobilized TiO2 systems and mixed pesticides degradation studies. At the end of the reaction methyl parathion and its by-products were completely degraded. During lindane degradation hexachloro cyclohexane, pentachloro cyclohexane, hexachloro benzene, 1-hydroxy 2,3,4,5,6-chlorocyclohexane, 1-hydroxy 2,3,4,5,6-chlorobenzene, pentachloro cyclopentadiene, 1,2,3,4,5-hydroxy cyclopentene and 1,2,3-hydroxy cyclobutane were identified in suspended and immobilized TiO2 systems, whereas only hexachloro cyclohexane, pentachloro cyclohexane, hexachloro benzene and pentachloro cyclopentadiene were observed during mixed pesticides degradation. No intermediate by-product was observed during the photo degradation of dichlorvos. Langmuir-Hinshelwood pseudo first order kinetic equation showed that there was not much change in the rates of degradation in both suspended and immobilized TiO2 systems irrespective of the pesticide. During mixed pesticides degradation, the degradation pattern was not similar to that of single pesticide. 相似文献
44.
UV/TiO2/H2O2, UV/TiO2 and UV/H2O2 were compared as pre-treatment processes for the detoxification of mixtures of 4-chlorophenol (4CP), 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TCP) and pentachlorophenol (PCP) prior to their biological treatment. When each chlorophenol was initially supplied at 50 mg l−1, UV/TiO2/H2O2 treatment supported the highest pollutant removal, COD removal, and dechlorination efficiencies followed by UV/TiO2 and UV/H2O2. The remaining toxicity to Lipedium sativum was similar after all pre-treatments. Chlorophenol photodegradation was always well described by a first order model kinetic (r2 > 0.94) and the shortest 4CP, DCP, TCP and PCP half-lives of 8.7, 7.1, 4.5 and 3.3 h, respectively, were achieved during UV/TiO2/H2O2 treatment. No pollutant removal was observed in the controls conducted with H2O2 or TiO2 only. Inoculation of all the photochemically pre-treated mixtures with activated sludge microflora was followed by complete removal of the remaining pollutants. Combined UV/TiO2/H2O2-biological supported the highest detoxification, dechlorination (99%) and COD removal (88%) efficiencies. Similar results were achieved when each chlorophenol was supplied at 100 mg l−1. COD and Cl mass balances indicated UV, UV/H2O2, and UV/TiO2 treatments lead to the formation of recalcitrant photoproducts, some of which were chlorinated. 相似文献
45.
The synthesis of TiO2 and Fe–TiO2 by sol–gel method is demonstrated and characterized. The characterization of TiO2 and Fe–TiO2 is performed with instruments, including TGA/DTA, FTIR, UV–Vis, N2 adsorption and SEM. Dichloromethane is used for the photocatalytic activity test. From the results of dichloromethane photocatalyitc degradation, the calcined temperature of TiO2 and the presence of water vapor influence the photocatalytic activity. The optimum doping amount of iron ions is 0.005 mol%, and this can enhance the photocatalytic activity, while too great an amount will make the iron ions become recombination centers for the electron–hole pairs and reduce the photocatalytic activity. UV–Vis diffuse reflectance spectra of Fe–TiO2 show an increase in absorbency in the visible light region with the increase in iron ions doping concentration The intermediate of dichloromethane photodegradation includes CHCl3, CCl4, CH2Cl2 and COCl2. The presence of iron ions may reduce the adsorption of Cl element on the surface of the photocatalyst. 相似文献
46.
Xi Chen Jieqiong Wang Jingwen Chen Chengzhi Zhou Feifei Cui Guoxin Sun 《环境科学学报(英文版)》2019,31(11):129-137
Benzotriazole UV stabilizers (BT-UVs) have attracted concerns due to their ubiquitous occurrence in the aquatic environment, and their bioaccumulative and toxic properties. However, little is known about their aquatic environmental degradation behavior. In this study, photodegradation of a representative of BT-UVs, 2-(2-hydroxy-5-methylphenyl)benzotriazole (UV-P), was investigated under simulated sunlight irradiation. Results show that UV-P photodegrades slower under neutral conditions (neutral form) than under acidic or alkaline conditions (cationic and anionic forms). Indirect photodegradation is a dominant elimination pathway of UV-P in coastal seawaters. Dissolved organic matter (DOM) from seawaters accelerate the photodegradation rates mainly through excited triplet DOM (3DOM?), and the roles of singlet oxygen and hydroxyl radical are negligible in the matrixes. DOM from seawaters impacted by mariculture exhibits higher steady-state concentration of 3DOM? ([3DOM?]) relative to those from pristine seawaters, leading to higher photosensitizing effects on the photodegradation. Halide ions inhibit the DOM-sensitized photodegradation of UV-P by decreasing [3DOM?]. Photodegradation half-lives of UV-P are estimated to range from 24.38 to 49.66?hr in field water bodies of the Yellow River estuary. These results are of importance for assessing environmental fate and risk UV-P in coastal water bodies. 相似文献
47.
Chunyan Yu Hua Wang Xuan Liu Xie Quan Shuo Chen Jianlin Zhang Peng Zhang 《环境科学学报(英文版)》2014,26(7):1383-1388
To elucidate the effect of nitrite ion (NO2^-) on the photodegradation of organic pollutants, a 300 W mercury lamp and Pyrex tubes restricting the transmission of wavelengths below 290nm were used to simulate sunlight, and the photodegradation processes of 2,4-dichlorophenoxyacetic acid (2,4-D) with different concentrations of NO2^- in freshwater and seawater were studied. The effect of reactive oxygen species (ROS) on the photolysis of 2,4-D was also demonstrated using electron paramagnetic resonance (EPR). The results indicated that the 2,4-D photolysis reaction followed the first-order kinetics in freshwater and seawater under different concentrations of NO2^-. Meanwhile, the photochemical reaction rate of 2,4-D increased with increasing concentration of NO2^-. When the concentration of NO2^- was lower than 23 mg/L, the photodegradation rate of 2,4-D in seawater was higher than that in freshwater. However, when the concentration of NO2^- was reached 230 mg/L, 2,4-D degradation slowed down in seawater. It was important to note that EPR spectra showed NO2 radical was generated in the NO5 solution under simulated sunlight irradiation, indicating that 2,4-D photodegradation could be induced by NO2. These results show the key role of NO2^- in photochemistry and are helpful for better understanding of the phototransformation of environmental contaminants in natural aquatic systems. 相似文献
48.
Kinetics of nitromusk compounds degradation in water by ultraviolet radiation and hydrogen peroxide 总被引:2,自引:0,他引:2
The photodegradation of five representative nitromusk compounds in water has been performed in a stirred batch photoreactor with a UV low-pressure immersed mercury lamp, at constant temperature and different doses of hydrogen peroxide. The rate constants have been calculated on the basis of experimental data and a postulated first-order kinetic model. The rate constants, at 298 K and a dose of 1.1746 μmol l−1 H2O2 ranges from 0.3567 × 10−3 s−1 for musk tibetene, to 1.785 × 10−3 s−1 for musk ambrette. 相似文献
49.
ZnBiYO4 was synthesized by a solid-state reaction method for the first time. The structural and photocatalytic properties of ZnBiYO4 were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and UV–Vis diffuse reflectance. ZnBiYO4 crystallized with a tetragonal spinel structure with space group I41/A. The lattice parameters for ZnBiYO4 were a = b = 11.176479 Å and c = 10.014323 Å. The band gap of ZnBiYO4 was estimated to be 1.58 eV. The photocatalytic activity of ZnBiYO4 was assessed by photodegradation of methyl orange under visible light irradiation. The results showed that ZnBiYO4 had higher catalytic activity compared with N-doped TiO2 under the same experimental conditions using visible light irradiation. The photocatalytic degradation of methyl orange with ZnBiYO4 or N-doped TiO2 as catalyst followed first-order reaction kinetics, and the first-order rate constant was 0.01575 and 0.00416 min− 1 for ZnBiYO4 and N-doped TiO2, respectively. After visible light irradiation for 220 min with ZnBiYO4 as catalyst, complete removal and mineralization of methyl orange were observed. The reduction of total organic carbon, formation of inorganic products, SO42 − and NO3−, and evolution of CO2 revealed the continuous mineralization of methyl orange during the photocatalytic process. The intermediate products were identified using liquid chromatography–mass spectrometry. The ZnBiYO4/(visible light) photocatalysis system was found to be suitable for textile industry wastewater treatment and could be used to solve other environmental chemical pollution problems. 相似文献
50.
MUKESH KUMAR RAIKWAR SUBIR KUMAR NAG 《Journal of environmental science and health. Part. B》2013,48(6):973-988
Photodegradation of alphacypermethrin ((RS)-α cyano-3-phenoxy benzyl (1RS) cis-3-(2,2,dichlorovinyl)-2,2-dimethyl cyclopropane carboxylate) was studied as a thin film on glass surface and on black and red soil surfaces. A number of photoproducts from glass surfaces have been isolated, characterized and identified by gas chromatography-mass spectroscopy (GC-MS). However, only two of them viz. 3-phenoxy benzyl alcohol and [2,2-dichlorovinyl-3(2,2,dimethyl) cyclopropane carboxylate] could be identified from both the soil. Rate of photodegradation on glass and soil surface under UV and sunlight followed first order kinetics with significant correlation coefficients. The rate of photodegradation was greater on black than on red soil. 相似文献