Photodegradation of fluoroquinolones in aqueous solution under light conditions relevant to surface waters,toxicity assessment of photoproduct mixtures

Environmental Science and Pollution Research - Photochemical degradation of fluoroquinolones ciprofloxacin, enrofloxacin and norfloxacin in aqueous solution under light conditions relevant to...     

Reduction of Cr(VI) by malic acid in aqueous Fe-rich soil suspensions

Detoxification of Cr(VI) through reduction by organic reductants has been regarded as an effective way for remediation of Cr(VI)-polluted soils. However, such remediation strategy would be limited in practical applications due to the low Cr(VI) reduction rate. In this study, the catalytic effect of two Fe-rich soils (Ultisol and Oxisol) on Cr(VI) reduction by malic acid was evaluated. As the results shown, the two soils could obviously accelerate the reduction of Cr(VI) by malic acid at low pH conditions, while such catalytic effect was gradually suppressed as the increase in pH. After reaction for 48 h at pH 3.2, Oxalic acid was found in the supernatant of Ultisol, suggesting the oxidization of hydroxyl in malic acid to carboxyl and breakage of the bond between C₂ and C₃. It was also found that the catalytic reactivity of Ultisol was more significant than that of Oxisol, which could be partly attributed to the fact that the amount of Fe(II) released from the reductive dissolution of Ultisol by malic acid was larger than that of Oxisol. With addition of Al(III), the catalytic effect from Ultisol was inhibited across the pH range examined. On the contrary, the presence of Cu(II) would increase the catalytic effect of Ultisol, which was more pronounced with the increase in pH. This study proposed a potential way for elimination of the environmental risks posed by the Cr(VI) contamination by use of the natural soil surfaces to catalyze Cr(VI) reduction by the organic reductant such as malic acid, a kind of organic reductant originating from soil organic decomposition process or plant excretion.     

Photocatalytic degradation of five sulfonylurea herbicides in aqueous semiconductor suspensions under natural sunlight

In the present study, the photocatalytic degradation of five sulfonylurea herbicides (chlorsulfuron, flazasulfuron, nicosulfuron, sulfosulfuron and triasulfuron) has been investigated in aqueous suspensions of zinc oxide (ZnO), tungsten (VI) oxide (WO₃), tin (IV) oxide (SnO₂) and zinc sulfide (ZnS) at pilot plant scale under natural sunlight. Photocatalytic experiments, especially those involving ZnO photocatalysis, showed that the addition of semiconductors in tandem with the oxidant (Na₂S₂O₈) strongly enhances the degradation rate of the herbicides in comparisons carried out with photolytic tests. The degradation of the herbicides follows a first order kinetics according to the Langmuir-Hinshelwood model. In our conditions, the amount of time required for 50% of the initial pesticide concentration to dissipate (t_½) ranged from 8 to 27 min (t_30W = 0.3-1.2 min) for sulfosulfuron and chlorsulfuron, respectively in the ZnO/Na₂S₂O₈ system. None of the studied herbicides was found after 120 min of illumination (except chlorsulfuron, 0.2 μg L⁻¹).     

水中四环素类化合物在不同光源下的光降解

研究了模拟太阳光和实际室外太阳光下四环素类化合物在水溶液中的光降解。结果表明,四环素类化合物(TCs)在模拟太阳光照射下均能发生直接光降解,且其降解速率随pH不同变化很大。四环素(TC)、土霉素(OTC)、金霉素(CTC)和多西环素(DTC)的光降解速率随溶液pH升高明显加快,而米诺环素(MTC)在水中的光降解速率随溶液pH升高略有下降。天然水体pH范围内,模拟太阳光照下四环素类化合物表观光降解速率常数在0.004～0.026 min-1范围内,降解半衰期在26～136 min范围内。在室外实际太阳光照下,四环素类化合物光降解反应速率与太阳光强成正比例关系。晴朗无云天气下,四环素类化合物降解半衰期在春冬季节较长、夏季节较短;四环素在东江实际水体中表观光降解速率很快,在冬季晴天天气下,其平均半衰期仅为8.2 min。     

Azo-dyes photocatalytic degradation in aqueous suspension of TiO2 under solar irradiation

The photodegradation of two common and very stable azo-dyes, i.e. methyl-orange (C₁₄H₁₄N₃SO₃Na) and orange II (C₁₆H₁₁N₂SO₄Na), is reported. The photocatalytic oxidation was carried out in aqueous suspensions of polycrystalline TiO₂ irradiated by sunlight. Compound parabolic collectors, installed at the “Plataforma Solar de Almería” (PSA, Spain) were used as the photoreactors and two identical reacting systems allowed to perform photoreactivity runs for the two dyes at the same time and under the same irradiation conditions. The disappearance of colour and substrates together with the abatement of total organic carbon content was monitored. The main sulfonate-containing intermediates were found to be in lower number in respect to those obtained under artificial irradiation. In particular there were no more evidence of the presence of hydroxylated transients. The dependence of dye photooxidation rate on: (i) substrate concentration; (ii) catalyst amount; and (iii) initial pH was investigated. The influence of the presence of strong oxidant species (H₂O₂, S₂O₈²⁻) and some ions (Cl⁻, SO₄²⁻) on the process was also studied.     

Photodegradation of monochlorobenzene in titanium dioxide aqueous suspensions

The photocatalytic degradation of monochlorobenzene using titanium dioxide aqueous suspensions was performed under solar-simulated irradiation. The effects of concentration of monochlorobenzene, amount of titanium dioxide and pH of solution on the degradation were examined. The intermediates identified were three monochlorophenols, chlorohydroquinone and hydroxy-hydroquinone.     

Effect of various cyclodextrins on photodegradation of a hydrophobic herbicide in aqueous suspensions of different soil colloidal components

This paper investigated the photochemical behaviour of the herbicide norflurazon (NFL) in the presence of different soil colloidal components and several cyclodextrins (CDs). The interaction of NFL with CDs yielded the formation of inclusion complexes at 1:1 stoichiometric ratio in solution, with an increase of the herbicide solubility. The irradiation of NFL aqueous solutions in the presence of CDs showed that the higher the formation constant of NFL-CD complexes (Kc) and their solubility, the higher their photocatalytic effects, following the CDs in the order: RAMEB>HPBCD>beta-CD>alpha-CD>gamma-CD. The presence of the different soil colloidal components in aqueous suspension provoked the reduction of the NFL photodegradation rate, due to a screening effect, especially when goethite and humic acids were present. No disappearance of NFL was detected in parallel studies carried out in the dark, except in the case of humic acids, where a 5% adsorption of the initial amount of NFL was adsorbed in the dark control. The presence of the different CDs in such systems showed an inductive photodegradation effect on the herbicide. This could be largely explained by the inclusion effects of CDs in catalyzing interactions between NFL and certain reactive radicals generated by the different colloidal components. Although this work was carried out at laboratory scale and therefore, has limited applications, it reveals that cyclodextrins increase solubilization of hydrophobic herbicides and could lead to their increased photodegradation. This could be a promising method for pesticide-contaminated water remediation. However, it is important to consider the effect of the soil colloidal components in the different aquatic systems and their concentrations, since they can alter the photodegradative effects of the cyclodextrins.     

Photocatalytic oxidation of propoxur in aqueous titanium dioxide suspensions

Abstract

The photocatalytic oxidation of propoxur, a nitrogen‐containing pesticide, has been investigated using aqueous TiO₂ suspensions as catalyst in this study. The operating variables considered in the study were initial pH, temperature, [H₂O₂] and TiO₂ loading. Results showed that 1 g/l of TiO₂ was the optimum dosage for oxidizing propoxur in this system. Hydrogen peroxide can increase the oxidation rate with increasing its initial concentration. There was no obvious difference in the rate of propoxur oxidation at the initial pH of 4, 6 and 9, and the final pHs of reaction solutions were around 5.5. However, propoxur degraded slower at initial pH 2, and the pH did not vary during the period of photocatalytic reaction. The photocatalytic oxidation of propoxur using TiO₂ suspensions as the photocatalyst was reaction‐controlled as indicated by the activation energy.     

太阳光/CuMnFe LDHs催化剂/过一硫酸盐体系降解双酚A

利用水热法合成了具有高催化活性的CuMnFe三元金属氢氧化物(LDHs)催化剂,确定了最佳的Cu、Mn、Fe摩尔比,通过XRD、XPS、UV-vis DRS、FT-IR、SEM、TEM、BET等方法对催化剂进行了表征,并探究了催化剂投加量、PMS浓度、溶液pH、阴离子的种类和浓度对体系BPA去除的影响,进而通过LC-M...     

Stability of titania nanoparticles in soil suspensions and transport in saturated homogeneous soil columns

The stability of TiO₂ nanoparticles in soil suspensions and their transport behavior through saturated homogeneous soil columns were studied. The results showed that TiO₂ could remain suspended in soil suspensions even after settling for 10 days. The suspended TiO₂ contents in soil suspensions after 24 h were positively correlated with the dissolved organic carbon and clay content of the soils, but were negatively correlated with ionic strength, pH and zeta potential. In soils containing soil particles of relatively large diameters and lower solution ionic strengths, a significant portion of the TiO₂ (18.8-83.0%) readily passed through the soils columns, while TiO₂ was significantly retained by soils with higher clay contents and salinity. TiO₂ aggregate sizes in the column outflow significantly increased after passing through the soil columns. The estimated transport distances of TiO₂ in some soils ranged from 41.3 to 370 cm, indicating potential environmental risk of TiO₂ nanoparticles to deep soil layers.     

Azo-dyes photocatalytic degradation in aqueous suspension of TiO2 under solar irradiation

The photodegradation of two common and very stable azo-dyes, i.e. methyl-orange (C₁₄H₁₄N₃SO₃Na) and orange II (C₁₆H₁₁N₂SO₄Na), is reported. The photocatalytic oxidation was carried out in aqueous suspensions of polycrystalline TiO₂ irradiated by sunlight. Compound parabolic collectors, installed at the “Plataforma Solar de Almería” (PSA, Spain) were used as the photoreactors and two identical reacting systems allowed to perform photoreactivity runs for the two dyes at the same time and under the same irradiation conditions. The disappearance of colour and substrates together with the abatement of total organic carbon content was monitored. The main sulfonate-containing intermediates were found to be in lower number in respect to those obtained under artificial irradiation. In particular there were no more evidence of the presence of hydroxylated transients. The dependence of dye photooxidation rate on: (i) substrate concentration; (ii) catalyst amount; and (iii) initial pH was investigated. The influence of the presence of strong oxidant species (H₂O₂, S₂O₈²⁻) and some ions (Cl⁻, SO₄²⁻) on the process was also studied.     

Photolytic degradation of quinalphos in natural waters and on soil matrices under simulated solar irradiation

The photochemical persistence of quinalphos, one of the most widely used organophosphorous insecticides, was investigated in a variety of environmental matrices such as natural waters and soils of different composition. Simulated solar irradiation was obtained using a xenon arc lamp (Suntest CPS+ apparatus) giving an irradiation intensity of 750 W m(-2) equivalent to a light dose per hour of irradiation of 2,700 kJ m(-2). The phototransformation rates were determined using solid-phase microextraction (SPME) and ultrasonic extraction (USE) coupled to GC-FTD, while the identification of photoproducts was carried out by GC-MS. In water samples, the degradation kinetics followed a pseudo-first-order reaction and photolysis half-lives ranged between 11.6 and 19.0 h depending on the constitution of the irradiated media. Dissolved organic matter (DOM) has a predominant retarding effect, while nitrate ions accelerated the photodegradation kinetics. In soil samples, the degradation kinetics was monitored on 1mm soil layer prepared on glass TLC plates. The kinetic behaviour of quinalphos was complex and characterized by a double step photoreaction, fast in the first 4h of irradiation followed by a slow degradation rate up to 64 h. The photolysis half-life of quinalphos was shorter in sandy soil compared to the rest of the soil samples, varying between 16.9 and 47.5 h, and showing a strong dependence on the composition of the irradiated media. Among the transformation products formed mainly through photohydrolysis and photoisomerization processes, some photoproduct structures were proposed according to their mass spectral information.     

Photostability of methidathion in wet soil amended with biosolid and a surfactant under solar irradiation

Photodegradation studies of the organophosphorous insecticide methidathion in thin layers of wet soil samples have been carried out under solar irradiation. Soil samples consisted of an agricultural soil added with two amendments: a municipal biosolid and the cationic surfactant TDTMA (tetradecyl trimethyl ammonium bromide). Dark controls of the different soil treatments were also considered. Soil and biosolid samples were previously autoclaved to eliminate biotic degradation. In this study we investigated the role of these amendments in methidathion photodegradation which is a rapid (<7 days) and indirect process. Although scarce differences were found between non-amended and amended samples, methidathion from soil exposed under sunlight is degraded more quickly than in dark conditions. Photodegradation products (methidathion oxon GS 13007 and GS 12956) were not detected.     

Formation of nitrophenols upon UV irradiation of phenol and nitrate in aqueous solutions and in TiO2 aqueous suspensions.

The formation of nitrophenols was studied as a consequence of ultra violet (UV) irradiation of aqueous solutions of phenol and nitrate in the range of pH 1-12. The study was performed both in homogeneous phase and in the presence of water-suspended TiO2. The effects of pH, dissolved oxygen and 2-propanol as .OH scavenger have been evaluated. A reaction mechanism is proposed, based on the experimental results.     

ZnIn2S4可见光催化降解水中的双氯芬酸

通过水热法制备了可见光下响应的光催化剂ZnIn2S4,研究了水中痕量医药类物质双氯芬酸的光解和光催化降解效果与降解途径,同时对催化剂进行了扫描电镜、X射线衍射、紫外可见漫反射、氮吸附和羟基自由基捕获的测试。结果表明,ZnIn2S4的比表面积为91.3 m2·g-1,且在可见光照射下具有良好光催化性能。以卤钨灯模拟太阳光,在双氯芬酸初始浓度100 μg·L-1,ZnIn2S4投加浓度10 mg·L-1条件下反应5 h可降解水中98%的双氯芬酸。卤钨灯直接光解5 h可降解91%的双氯芬酸。光解和光催化反应均符合假一级反应动力学,光催化反应速率是光解反应速率的1.5倍。双氯芬酸光解过程中主要发生光环化反应,生成了2-（1-氯-9H-咔吧唑-8-基）-乙酸;光催化过程则主要通过羟基自由基氧化降解双氯芬酸,中间产物主要有1-氯-8-甲基-9H-咔吧唑及2,6-二氯-N-邻甲苯基苯胺。     

Microbial metabolism of N-Phenyl-1-naphthylamine in soil, soil suspensions, and aquatic ecosystems

N-Phenyl-1-naphthylamine (PNA) was degraded and mineralized in nonsterile aquatic and terrestrial samples. Degradation in unsupplemented sewage and lake water was detected in 3 to 6 days with half-lives of 5 and 10 days, respectively. In sewage and lake water supplemented with a readily degradable carbon source, degradation began in 1 and 5 days with half-lives of 2 and 8 days, respectively. Sewage samples converted between 20 and 30% of labeled [¹⁴C]-PNA to ¹⁴CO₂ in 35 days while lake water samples reached 10% conversion to ¹⁴CO₂ in 12 days. Soil samples and soil suspensions converted from 15 to 35% of [¹⁴C]-PnA to ¹⁴CO₂ in 11 days. PNA was microbiologically converted in lake water to two products that were tentatively identified by gas-liquid chromatography and mass spectroscopy as dihydroxy and N-acetyl derivatives.     

模拟日光下铌酸盐/钛酸纳米片催化降解水中环丙沙星

通过一步水热法制备新型铌酸盐/钛酸纳米片(Niobate/titanate nanoflakes,Nb-TiNFs)复合材料,采用XRD、XPS、FT-IR、SEM、TEM等分析手段对其形貌和结构进行了表征,并探究其在模拟日光下对目标污染物环丙沙星(ciprofloxacin,CIP)的降解性能和内在反应机理。结果表明,Nb-TiNFs可高效、快速光催化降解水中CIP。溶液pH可通过影响静电作用以及羟基自由基的形成而影响CIP的降解,在pH为6时,光催化剂(0.1 g·L⁻¹)对水中CIP(10 mg·L⁻¹)的降解率最大,即180 min内达到96.2%;常规离子Na⁺和Fe³⁺对CIP的降解无明显影响,但Ca²⁺的存在对其产生一定抑制作用。降解过程中,超氧自由基(·O₂⁻)是主要的活性物质,材料内部形成的异质结导致带隙偏移,促进电子转移,抑制电子-空穴对的复合,从而促进了太阳光驱动的光催化活性。Nb-TiNFs合成方法简单、高效、稳定且对环境友好,在光催化去除水中新兴污染物领域具有一定的应用前景。     

Fenarimol solar degradation pathways and photoproducts in aqueous solution

The degradation photoproducts of the fungicide fenarimol obtained from irradiation of aqueous solutions with sunlight were characterised. The photoproducts resulting from samples with different exposure times were extracted and separated using chromatographic techniques. Seven main photoproducts were detected using high performance liquid chromatography with a photodiode array detector, gas chromatography with mass spectrometry detector and Fourier transform infrared spectroscopy. Structures are suggested for possible photoproducts based on the characterisation results, minimum energy geometry of the parent compound, and the mass spectral behaviour of fenarimol. These correspond to the compounds with m/z 328 (three structural isomers (a), (b) and (c)), m/z 294 (two structural isomers (a) and (b)), m/z 292, 278 and 190. Of the various major products detected, the isomer 328(a) is seen to be particularly unstable under the action of sunlight. The most stable photoproducts are found to be those with m/z 294(a), 278 and 190. However, upon prolonged solar irradiation all of these break down to produce polar, low molecular weight compounds. Comparison with our own and other results on fenarimol photolysis indicate significant solvent effects on the process. The combination of these structural characterisation results and previous data from spectroscopic and photodegradation kinetics studies allows us to suggest some possible mechanisms for the photodegradation of fenarimol under sunlight.     

Photodegradation of azithromycin in various aqueous systems under simulated and natural solar radiation: kinetics and identification of photoproducts

This article describes the photolysis of azithromycin, a macrolide antibiotic with reported occurrence in environmental waters, under simulated solar radiation. The photodegradation followed first-order reaction kinetics in five matrices examined. In HPLC water, the degradation rate was the slowest (half-life: 20 h), whereas in artificial freshwater supplemented with nitrate (5 mg L⁻¹) or humic acids (0.5 mg L⁻¹) the degradation of azithromycin was enhanced by factors of 5 and 16, respectively, which indicated the role of indirect photolysis involving the formation of highly reactive species. Following chromatographic separation on a UPLC system, the characterization of the transformation products was accomplished using high-resolution QqToF-MS analysis. The presence of seven photoproducts was observed and their formation was postulated to originate from (bis)-N-demethylation in the desosamine sugar, O-demethylation in the cladinose sugar, combinations thereof, as well as from hydrolytic cleavages of the desosamine and/or cladinose residue. Two of these photoproducts could also be detected in natural photodegradation process in river water which was spiked with azithromycin.     

Photocatalytic degradation of contaminants of concern with composite NF-TiO2 films under visible and solar light

This study reports the synthesis and characterization of composite nitrogen and fluorine co-doped titanium dioxide (NF-TiO₂) for the removal of contaminants of concern in wastewater under visible and solar light. Monodisperse anatase TiO₂ nanoparticles of different sizes and Evonik P25 were assembled to immobilized NF-TiO₂ by direct incorporation into the sol–gel or by the layer-by-layer technique. The composite films were characterized with X-ray diffraction, high-resolution transmission electron microscopy, environmental scanning electron microscopy, and porosimetry analysis. The photocatalytic degradation of atrazine, carbamazepine, and caffeine was evaluated in a synthetic water solution and in an effluent from a hybrid biological concentrator reactor (BCR). Minor aggregation and improved distribution of monodisperse titania particles was obtained with NF-TiO₂-monodisperse (10 and 50 nm) from the layer-by-layer technique than with NF-TiO₂?+?monodisperse TiO₂ (300 nm) directly incorporated into the sol. The photocatalysts synthesized with the layer-by-layer method achieved significantly higher degradation rates in contrast with NF-TiO₂-monodisperse titania (300 nm) and slightly faster values when compared with NF-TiO₂-P25. Using NF-TiO₂ layer-by-layer with monodisperse TiO₂ (50 nm) under solar light irradiation, the respective degradation rates in synthetic water and BCR effluent were 14.6 and 9.5?×?10^?3?min^?1 for caffeine, 12.5 and 9.0?×?10^?3?min^?1 for carbamazepine, and 10.9 and 5.8?×?10^?3?min^?1 for atrazine. These results suggest that the layer-by-layer technique is a promising method for the synthesis of composite TiO₂-based films compared to the direct addition of nanoparticles into the sol.