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 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.     

Photodegradation of hydroxyfluorenes in ice and water: A comparison of kinetics,effects of water constituents,and phototransformation by-products

The photochemical behavior of organic pollutants in ice is poorly studied in comparison to aqueous photochemistry.Here we report a detailed comparison of ice and aqueous photodegradation of two representative OH-PAHs,2-hydroxyfluorene (2-OHFL) and 9-hydroxyfluorene (9-OHFL),which are newly recognized contaminants in the wider environment including colder regions.Interestingly,their photodegradation kinetics were clearly influenced by whether they reside in ice or water.Under the same simulated s...     

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     

The degradation of plastic litter in rivers: Implications for beaches

Polythene sheeting is a major litter component on estuarine beaches and river banks. Sanitary towel backing strips, which are one of the commonest items of sewage related debris found on beaches, enter the riverine system via combined sewer overflows. Investigations on these items, positioned at natural riverine stranding levels, showed that after an initial rapid breakdown little further loss of tensile strength occurred. Experiments carried out on backing strips, buried in the bank suspended from a tree and tethered to the bank, showed significant change. Buried samples retained the greatest tensile strength retention, dropping no lower than 90 %, the other samples showed similar retention rates at 80%. The difference is probably due to photodegradation as biodegradation effects were minimal. Probably, the longevity of such plastics is a major reason for their abundance and widespread distribution both on river banks and beaches.     

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.     

不锈钢负载TiO2薄膜光降解印染废水

以TiO2为催化剂,将其制膜固定在不锈钢质光反应器内壁上,以125W高压汞灯为光源,对武汉市某丝绸厂的印染废水进行了处理实验.取得了脱色率100%,CODCr去除率83.4%的效果,并探讨了多种因素对光降解的影响.     

Kinetic studies of imazapyr photolysis and characterization of the main photoproducts

The fate of imazapyr (2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid), a broad-spectrum herbicide in the imidazolinone family, has been studied upon UV irradiation. Most of the photoproducts occurring during the photodegradation have been characterized by means of liquid chromatography and mass spectrometry coupled techniques (LC-MS). The use of high resolution mass spectrometry has allowed to maximize the chemical information obtained from a single LC-MS analysis. The degradation of a 10?ppm imazapyr solution leads to pyridine derivatives which remain in solution during 50–100?h while the imazapyr is completely degraded after 6?h.