Photodegradation of atrazine and ametryn with visible light using water soluble porphyrins as sensitizers

The photodegradation of the herbicides atrazine and ametryn with visible light in aerated neutral aqueous solutions and 5, 10, 15, 20-tetrakis (2,6-dichloro-3-sulfophenyl) porphyrin or 5, 10, 15, 20-tetrakis (4-sulfophenyl) porphyrin as sensitizers are reported for the first time. Our findings show that the degradation percentage reached 30% for atrazine and 63% for ametryn. The final photoproducts were characterized as dealkylated s-triazines. Photolysis of the pesticides in the presence of a singlet oxygen quencher showed only a minor contribution of this type of mechanism, while a bimolecular quenching reaction between the triplet state of the sensitizer and the pesticides is excluded by flash photolysis studies. It is proposed that the mechanism may involve the formation of a superoxide radical anion from the triplet state of the sensitizer and molecular oxygen, followed by a radical decomposition pathway. Selected article from 1st International Meeting on Photochemistry, Photocatalysis and Environmental Applications, Agadir, 2006, organised by Prof. Dr. Ait Ichou, University Ibn Zohr, Agadir, Morocco     

光-生物双降解聚苯乙烯泡沫塑料降解性研究

研究了一种用来制造快餐盒的光－生物双降解聚苯乙烯（ＰＳ）发泡塑料的降解性能及其影响因素，结果表明：双解ＰＳ样品能在可见光照射下发生光降解。在真菌作用下发生微生物降解，光降解对微生物降解无明显促进作用，真菌能够利用双解ＰＳ表面和内部的改性淀粉，双解ＰＳ片材与餐盒在重量变化率上的显著差异揭示了生产过程中的机械冲压是餐盒微生物降解性能降低的主要原因。     

Photolysis of spinosyns in seawater, stream water and various aqueous solutions

Spinosad, a reduced-risk insecticide, contains primarily two active compounds, spinosyns A and D that are fermentation products of bacterium Saccharopolyspora spinosa. It is currently used to control fruit flies in Hawaii, USA. In this study, we investigated photodegradation of spinosyns A and D, respectively, in seawater, stream, tap and distilled-deionized waters under various light sources. Photodegradation of the two chemicals was also studied in various aqueous solutions prepared with phosphate buffer at different pH or chemical sensitizers. Two major photolytic products from spinosyn A were detected as spinosyn B and hydroxylated spinosyn A. Spinosyn D was similarly hydroxylated and N-demethylated. Spinosyns A and D were photodegraded rapidly under sunlight in Hawaii, USA. The half-life of spinosyns A and D in stream water was 1.1 and 1.0 h, respectively, and was a half of that in distilled-deionized water, 2.2 and 2.0 h, respectively. Photodegradation of spinosyns A and D followed an order of increasing rate constants in distilled-deionized, seawater, stream and tap water under 300 nm artificial light, and was enhanced approximately 8- and 17-fold, respectively, in acetone-sensitized solution as compared to in distilled-deionized water. Photolysis rates of spinosyns A and D in isopropanol- or humic acid-fortified water did not differ much as compared with those accordingly in distilled-deionized water. Spinosyns A and D photodegraded slower in acidic aqueous solution than in basic aqueous solution.     

Photodegradation of new amino acid derivatives suitable for chelating agents in pulp bleaching applications

The purpose of this study was to evaluate photodegradabilities of the following new low-nitrogen chelating agents: N-bis[(carboxymethoxy)ethyl]glycine (compound 1), N-bis[(1,2-dicarboxyethoxy)ethyl]glycine (compound 2) and N-bis[(1,2-dicarboxyethoxy)ethyl]aspartic acid (compound 3). At first photodegradation of these chelating agents as uncomplexed Na-compound 1–3 and Cu(II) complexes were tested, both in lake and distilled water, by exposing them to near-UV region radiation at the range of 315–400 nm. Uncomplexed Na-compounds 2 and 3 were selected to sunlight exposure experiments carried out in lake and distilled water. Compound 3 was also tested in sunlight as Cu and Ca complexes in both solutions. Photodegradation of Na₆-compound 3 in distilled water was studied by exposing it to radiation at the wavelength of 253.7 nm. Photodegradation products were analysed by means of GC-MS (gas chromatography with mass selective detector).

The results demonstrated that compound 1 was quite photostable even as Cu complex while compounds 2 and 3 were found to be photodegradable. Over 90% reduction of compound 3 was achieved during one week and 80% reduction of compound 2 in two weeks' time when they were added as Na salt to lake water and exposed to sunlight. Compound 3 as Cu complex degraded totally in the sunlight in less than one week. In the case of compound 3, the degradation rate decreased depending on the counter cation in the order Cu > Na  Ca. The study demonstrated that photodegradation of Na₆-compound 3 does not result in total mineralization of the compound. A photodegradation pathway for Na₆-compound 3 is proposed.     

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  and c = 10.014323 . The band gap of ZnBiYO4 was estimated to be 1.58 e V. 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 Ti O2 under the same experimental conditions using visible light irradiation. The photocatalytic degradation of methyl orange with ZnBiYO4 or N-doped Ti O2 as catalyst followed first-order reaction kinetics, and the first-order rate constant was 0.01575 and 0.00416 min-1for ZnBiYO4 and N-doped Ti O2, 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, SO2-4and NO-3, 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.     

Effects of fulvic acid concentration and origin on photodegradation of polycyclic aromatic hydrocarbons in aqueous solution: Importance of active oxygen

With an Xe arc lamp house as simulated sunlight, the influences of fulvic acid (FA) concentration and origins on photodegradation of acenaphthene, fluorine, phenanthrene, fluoranthene and pyrene in aqueous solution have been studied. Similar effects of FAs, collected from five places around China, on polycyclic aromatic hydrocarbon (PAH) photodegradation have been observed. Active oxygen was of significance in PAH photodegradation with the presence of FAs. For systems with 1.25 mg L⁻¹ FAs, the contributions of OH to PAH photodegradation rates were from 33% to 69%. FAs had two opposite effects, i.e., stimulating the generation of active oxygen and advancing PAH photodegradation; competing with PAHs for energy and photons and restraining PAH photodegradation. Generally, photodegradation rates of the 5 PAHs decreased with the increase of FAs concentration; except fluoranthene and pyrene were advanced in solutions with low FA concentration. The influences of FA concentration on PAH photodegradation were more significant than FA origin.     

Direct and indirect photolysis of two quinolinecarboxylic herbicides in aqueous systems

The photodegradation of two quinolinecarboxylic herbicides, 7-chloro-3-methylquinoline-8-carboxylic acid (QMe) and 3,7-dichloroquinoline-8-carboxylic acid (QCl), was studied in aqueous solution at different irradiation wavelengths. The effect of sunlight irradiation was investigated also in the presence of titanium dioxide (TiO₂). UV irradiation degraded rapidly QMe affording 7-chloro-3-methylquinoline (MeQ) through a decarboxylation reaction. The reaction rate was lower in the presence of dissolved organic carbon (DOC) because of the adsorption of the herbicide on the organic components. Instead, QCl was stable under both UV light and sunlight irradiation. The irradiation of QMe or QCl solutions with simulated sunlight in the presence of TiO₂ produced the complete mineralization of the two herbicides.     

Photodegradation of perfluorooctanoic acid by synthesized TiO2-MWCNT composites under 365nm UV irradiation

Degradation of perfluorooctanoic acid (PFOA) is of great importance due to its global distribution, persistence and toxicity to bioorganisms. In present study, a composite TiO₂ with multiple wall carbon nano-tubes (MWCNTs) was synthesized using sol-gel method and it was used as photocatalyst to degrade PFOA in water. The prepared composite catalyst displayed significant absorption in UV to visible light region. The loading content of TiO₂ on MWCNTs could be adjusted by changing the ratio of precursor to MWCNTs. Due to the combined effect of the adsorption ability and e⁻ transport capacity of MWCNT, the composites displayed much higher photocatalytic ability to PFOA as compared to pure TiO₂ under UV irradiation. The photocatalyst prepared with 10:1 of tetrabutyl titanate/MWCNT was the most effective. With the optimal dosage at 1.6 g L⁻¹, almost 100% of PFOA was degraded in acid medium after irradiation for 8 h. It was proposed that PFOA were mainly degraded by stepwise losing a moiety of CF₂.     

Photolysis of Enrofloxacin in aqueous systems under simulated sunlight irradiation: Kinetics, mechanism and toxicity of photolysis products

Photolysis of Enro in water was investigated under simulated sunlight irradiation using a Xenon lamp. The results showed that Enro photolysis followed apparent first-order kinetics. Increasing Enro concentration from 5.0 to 40.0 mg L⁻¹ led to the decrease of the photolysis rate constant from 1.6 × 10⁻² to 3.0 × 10⁻³ min⁻¹. Compared with the acidic and basic conditions, the photolysis rate was faster at neutral condition. Both of nitrate and humic acid can markedly decrease the photolysis rate of Enro because they can competitively absorb photons with Enro. The electron spin resonance and reactive oxygen species scavenging experiments indicated that Enro underwent self-sensitized photooxidation via OH and ¹O₂. After irradiation for 90 min, only 13.1% reduction of TOC occurred in spite of fast photolysis of 58.9% of Enro, indicating that Enro was transformed into intermediates without complete mineralization. The photolysis of Enro involved three main pathways: decarboxylation, defluorination, and piperazinyl N⁴-dealkylation. The bioluminescence inhibition rate using Vibrio fischeri increased to 67.2% at 60 min and then decreased to 56.9% at 90 min, indicative of the generation of some more toxic intermediates than Enro and then the degradation of the intermediates. The results will help us understand fundamental mechanisms of Enro photolysis and provide insight into the potential fate and transformation of Enro in surface waters.     

UV-Vis/Fe(Ⅲ)/H2O2体系对水中雌酮的光降解

以250W照明金属卤化物灯为光源,研究了水中雌酮（E1）在UV-Vis／Fe（Ⅲ）／H2O2体系中的光降解;考查了初始pH、Fe（Ⅲ）、H2O2、E1初始浓度对E1光降解的影响。结果表明,UV-Vis／Fe（Ⅲ）／H2O2体系能有效地光降解E1,在[Fe（Ⅲ）30-20．8μmol／L、[H2O2]0=1664μmol／L、pH=3．0时,光照160min,18．5btmol／L E1的光降解率可达98．4%;在pH3．0～8．0范围内,pH初始值越小,E1降解率越大,反应初始速率越大;实验条件下,Fe（Ⅲ）、H2O2初始浓度越大,E1降解率越大,反应初始速率越大;E1初始浓度越低,E1降解率越大,反应初始速率越小。pH=3．0,实验浓度范围内的表观动力学方程为：dCE1／dt=0．00093[H2O2]^0.47[Fe（Ⅲ）]^0.62[E1]0.24;Fe（Ⅲ）是影响反应速率的主要浓度因素。