Kinetics of nitromusk compounds degradation in water by ultraviolet radiation and hydrogen peroxide

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.     

Photodegradation of Dyes in Aqueous Solutions containing Fe(III) -hydroxy Complex II. Solar Photodegradation Kinetics

The solar photodegradation of five dyes, C.I. reactive red 2, C.I. reactive blue 4, C.I. reactive black 8, C.I. basic red 13, and C.I. basic yellow 2, were studied in a sunlight/Fe(III)-hydroxy system. It was observed that the photodegradation of these five dyes were pseudo-first order reactions, which has a little difference with the photodegradation kinetics of the dyes with UV-light as the irradiation source. The comparison between the two studies is also conducted.     

水中isoproturon的紫外降解动力学研究

采用atrazine法测定了紫外反应装置的光强,通过H_2O_2法测定了装置的有效光程值。进而通过这些光强和光程,建立了低压紫外条件下水中常见的苯脲类除草剂—isoproturon的拟一级降解动力学模型。基于此,文章考察了不同紫外强度和不同pH下isoproturon的紫外降解特性。Isoproturon的紫外降解反应的拟一级反应速率常数随着紫外强度的增大而逐渐增加,进而求算得isoproturon的量子产率为0.00405 mol/einstein。溶液的p H在5~9范围内变化时,isoproturon的紫外降解效率不会受到显著影响。结果表明:增大紫外光强时可实现isoproturon这种新兴污染物的有效降解,而改变溶液的p H则无明显的提高效果。     

Photodegradation of malachite green and malachite green carbinol under irradiation with different wavelength ranges

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.     

Removal of mixed pesticides from drinking water system by photodegradation using suspended and immobilized TiO2

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.     

Sequential photochemical-biological degradation of chlorophenols

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.     

Study on photocatalytic degradation of gaseous dichloromethane using pure and iron ion-doped TiO2 prepared by the sol-gel method

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.     

Synthesis,crystal structure,photodegradation kinetics and photocatalytic activity of novel photocatalyst ZnBiYO4

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, SO₄^2 − 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.     

Phototransformation of Alphacypermethrin as Thin Film on Glass and Soil Surface∗

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.

     

Studies on enhanced degradable plastics. II. Weathering of enhanced photodegradable polyethylenes under marine and freshwater floating exposure

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.