排序方式: 共有75条查询结果,搜索用时 18 毫秒
41.
M.?DellaGrecaEmail author M.?Brigante M.?Isidori A.?Nardelli L.?Previtera M.?Rubino F.?Temussi 《Environmental Chemistry Letters》2003,1(4):237-241
The phototransformation of naproxen Na in aqueous medium has been investigated. Irradiation of the drug in drinking water affords seven photoproducts. Three of them are dimeric photoproducts isolated for the first time. The compounds, isolated by chromatographic processes, have been identified by spectroscopic means. The toxicity of the photoproducts and the parent drug has been assayed on Daphnia magna and Vibrio fischeri. The results indicate that some photoproducts are more toxic than naproxen. 相似文献
42.
Photodegradation (PD) of methylmercury (MMHg) is a key process of mercury (Hg) cycling in water systems, maintaining MMHg at a low level in water systems. However, we possess little knowledge of this important process in the Jialing River of Chongqing, China. In situ incubation experiments were thus performed to measure temporal patterns and influencing factors of MMHg PD in this river. The results showed that MMHg underwent a net demethylation process under solar radiation in the water column, which predominantly occurred in surface waters. For surface water, the highest PD rate constants were observed in spring (12 × 10− 3 ± 1.5 × 10− 3 m2/E), followed by summer (9.0 × 10− 3 ± 1.2 × 10− 3 m2/E), autumn (1.4 × 10− 3 ± 0.12 × 10− 3 m2/E), and winter (0.78 × 10− 3 ± 0.11 × 10− 3 m2/E). UV-A radiation (320–400 nm), UV-B radiation (280–320 nm), and photosynthetically active radiation (PAR, 400–700 nm) accounted for 43%–64%, 14%–31%, and 16%–45% of MMHg PD, respectively. PD rate constants varied substantially with the treatments that filtered the river water and amended it with chemicals (i.e., Cl−, NO3−, dissolved organic matter (DOM), Fe(III)), which reveals that suspended particulate matter and water components are important factors in affecting the PD process. For the entire water column, the PD rate constant determined for each wavelength range decreased rapidly with water depth. UV-A, UV-B, and PAR contributed 27%–46%, 6.2%–12%, and 42%–65% to the PD process, respectively. PD flux was estimated to be 4.7 μg/(m2·year) in the study site. Our results are very important to understand the cycling characteristics of MMHg in the Jialing River of Chongqing, China. 相似文献
43.
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
44.
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
45.
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
46.
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
47.
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
48.
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
49.
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
50.
The weatherability of three types of enhanced photodegradable polyethylene films and corresponding control films were studied under outdoor and marine floating conditions at two exposure sites. Progress of weathering was monitored using tensile elongation at break. In general, both the enhanced-degradable plastics and the corresponding controls degraded slower in marine exposure than in outdoor exposure. This is attributed to the lower sample temperatures (compared to samples exposed outdoors) and to shielding from light afforded by surface fouling in samples exposed floating in sea water. Enhanced-photodegradable polyethylenes disintegrated faster than the control samples in the case of both outdoor and marine exposures. The improvement obtained in marine exposures was greater than that for outdoor exposure of corresponding sample types. This is due to the extremely slow rates of disintegration of control films under marine floating conditions. 相似文献