Degradation of dye pollutants by immobilized polyoxometalate with H2O2 under visible-light irradiation

A Keggin polyoxometalate (POM, i.e., PW12O40(3-)) and its lacunary derivative are immobilized on an anionic exchange resin through electrostatic interaction at pH 4.6 in an aqueous dispersion. The resin-supported POM thus obtained catalyzes the efficient degradation of cationic dye pollutants in the presence of H2O2 under visible-light irradiation. To evaluate the photocatalytic system, degradation of a rhodamine B (RB) dye was investigated in detail using UV-visible spectroscopy, high performance liquid chromatography, and gas chromatography/mass spectrometry techniques to identify the intermediates and final products. Fluorescence lifetime measurements revealed the electron transfer from the visible-light-excited RB molecules to the POMs. Electron paramagnetic resonance measurements, investigation of the effects of *OH and *OOH scavengers on the photoreaction kinetics, and IR analysis indicated that de-ethylation of RB was due to *OOH radicals, but the decomposition of the conjugated xanthene structure was caused by the peroxo species formed by interaction of H2O2 with the lacunary POM loaded on the resin. A total organic carbon removal of ca. 22% was achieved, and the recycle experiment suggested excellent stability and reusability of the heterogeneous catalyst. On the basis of the experimental results, a photocatalytic mechanism is discussed.     

Photoproduction of hydroxyl radicals in aqueous solution with algae under high-pressure mercury lamp

Photoproduction of hydroxyl radicals (*OH) could be induced in aqueous solution with algae (Nitzschia hantzschiana, etc.) and (or not) Fe3+ under high-pressure mercury lamp with an exposure time of 4 h. *OH was determined by HPLC using benzene as a probe. The photoproduction of *OH increased with increasing algae concentration. Fe3+ could enhance the photoproduction of *OH in aqueous solution with algae. The results showed that the photoproduction of *OH in algal solution with Fe3+ was greater than that in algal solution without Fe3+. The light intensity and pH affected the photoproduction of *OH in aqueous solution with algae with/without Fe3+. The photoproduction of *OH in aqueous solution with algae and Fe3+ under 250 W was greater than that under 125 W HPML. The photoproduction of *OH in algal solution (pH ranged from 4.0 to 7.0) with (or not) Fe3+ at pH 4 was the greatest.     

Nitration and photonitration of naphthalene in aqueous systems

The nitration of naphthalene was studied in aqueous solution to gain insight into the processes leading to the nitration of aromatic compounds in atmospheric hydrometeors. Reactants used were nitric acid, nitrogen dioxide and peroxynitrous acid in the dark, nitrate, and nitrite/nitrous acid under illumination. Naphthalene nitration can lead to two possible isomers, 1- and 2-nitronaphthalene. The former nitrocompound preferentially forms upon electrophilic processes and in the presence of nitrogen dioxide. Electrophilic nitration of naphthalene takes place in the presence of concentrated nitric acid, but nitration with nitric acid and oxidants (charge-transfer nitration) occurs under much milder conditions than with nitric acid alone. Charge-transfer nitration may have some environmental significance in particular cases, e.g. in acidic aerosols in the presence of HNO3 and oxidants. Nitrogen dioxide is thought to have a role in PAH nitration in the Antarctic particulate matter. In previous papers we have found that nitration induced by peroxynitrous acid, HOONO, can follow two pathways, the former electrophilic (leading for instance to the formation of nitrophenols from phenol) and the latter probably involving HOONO itself (accounting for the formation of nitrobenzene from benzene). In the case of naphthalene and HOONO the electrophilic pathway mainly leads to 1-nitronaphthalene, while the other one preferentially yields 2-nitronaphthalene. The nitration of naphthalene in the presence of nitrite/nitrous acid under irradiation leads to both nitroisomers in similar ratios, and the process is not inhibited by hydroxyl scavengers. This excludes nitrogen dioxide as reactive species for nitration and marks a difference with phenol photonitration and a similarity with the behavior of benzene under comparable conditions. Nitrite photochemistry (and nitrite-induced photonitration as well) is expected to be relevant in fog and cloudwater in polluted areas. An important difference with the gas-phase nitration is that the radicals OH and NO3 are unlikely to play a relevant role in the nitration of naphthalene in aqueous solution.     

Photodegradation of dye pollutants catalyzed by porous K3PW12O40 under visible irradiation

Microporous solid K3PW12O40 is prepared by precipitation of phosphotungstic acid and potassium ion, followed by calcination. Using this material as photocatalyst, a series of dye pollutants, such as rhodamine B, malachite green, rhodamine 6G, fuchsin basic, and methyl violet, were efficiently degraded in the presence of H202 under visible light irradiation (lambda > 420 nm). The photocatalyst was characterized via SEM, BET surface area, FT-IR, and XRD. The photocatalyst has relative large surface area, and the Keggin structure of phosphotungstic ions is intact during the precipitation and calcination. The degradation kinetics, TOC changes, degradation products, ESR detection of active oxygen species, and the effect of radical scavengers are also investigated to clarify the degradation process and the reaction pathway. The dyes can be facilely bleached and mineralized (ca. 40% of TOC removal for RhB), and the main degradation products of RhB detected, besides CO2, are the small organic acids. They are released from the surface of the catalyst to the bulk solution during the degradation of the dye, which avoids the poisoning of photocatalyst by the intermediates. The formation of active oxygen species such as the O2-*/ HO2* and *OH are detected during the degradation of dye, and they are proposed to be responsible for the degradation of dyes. The K3PW12040 catalyst is very stable and very easily separated from the reaction system for reuse.     

聚氨酯泡沫固定化生物体系对活性蓝4的吸附脱色

为构建长效作用的生物脱色体系,采用聚氨酯泡沫(PUF)材料对生物吸附剂黄曲霉菌Aspergillus flavus A5p1进行固定化,以蒽醌染料活性蓝4(RB4)为模型底物,开展了生物吸附剂固定化前后的吸附动力学、不同RB4质量浓度和NaCl质量浓度对脱色的影响、重复使用脱色等实验的对比研究。结果表明：菌株经过固定化之后显著加快了对染料RB4的脱色,20 min时对200 mg/L染料RB4的吸附率达到77.8%,而未固定化的游离细胞90 min的吸附率为62.8%,脱色过程可采用颗粒内扩散动力学模型来描述;PUF-固定化细胞体系对2 000 mg/L染料RB4的吸附量约是游离细胞体系的2.5倍,并且能耐受NaCl质量浓度为50 g/L的高盐条件进行脱色;PUF-固定化细胞体系重复使用7次仍能保持89%的脱色率,而游离细胞体系则下降至74.3%,该PUF-固定化细胞体系展示出对提高RB4生物脱色的有效性及可靠性。     

Visible-light-driven photocatalytic inactivation of E. coli K-12 by bismuth vanadate nanotubes: bactericidal performance and mechanism

Bismuth vanadate nanotube (BV-NT), synthesized by a template-free solvothermal method, was used as an effective visible-light-driven (VLD) photocatalyst for inactivation of Escherichia coli K-12. The mechanism of photocatalytic bacterial inactivation was investigated by employing multiple scavengers combined with a simple partition system. The VLD photocatalytic bacterial inactivation by BV-NT did not allow any bacterial regrowth. The photogenerated h(+) and reactive oxidative species derived from h(+), such as OH(ads), H(2)O(2) and HO(2)/O(2)(-), were the major reactive species for bacterial inactivation. The inactivation by h(+) and OH(ads) required close contact between the BV-NT and bacterial cells, and only a limited amount of H(2)O(2) could diffuse into the solution to inactivate bacterial cells. The direct oxidation effect of h(+) to bacterial cells was confirmed by adopting F(-) surface modification and anaerobic experiments. The bacterial cells could trap e(-) in order to minimize e(-)-h(+) recombination, especially under anaerobic condition. Transmission electron microscopic study indicated the destruction process of bacterial cell began from the cell wall to other cellular components. The OH(ads) was postulated to be more important than OH(bulk) and was not supposed to be released very easily in the BV-NT bacterial inactivation system.     

Sources and sinks of hydroxyl radicals upon irradiation of natural water samples

Hydroxyl radical formation rates, steady-state concentration, and overall scavenging rate constant were measured by irradiation of surface lake water samples from Piedmont (NW Italy) and nitrate-rich groundwater samples from Moldova (NE Romania). Dissolved organic matter (DOM) was the main source and sink of *OH upon lake water irradiation, with [*OH] being independent of DOM amount. Water oxidation by photoexcited DOM is a likely *OH source in the presence of very low levels of nitrate and dissolved iron. Under different circumstances it is not possible to exclude other processes, e.g., DOM-enhanced photo-Fenton reactions. Under the hypotheses of no interaction and absence of mutual screening of radiation, nitrate would prevail over DOM as *OH source for a NO3-/DOM ratio higher than 3.3 x 10(-5) (mol NO3-) (mg C)(-1), DOM prevailing for lower values. Substantial DOM photolability was observed upon irradiation of nitrate-rich groundwater, mainly due to the elevated *OH generation rate. For the first time to our knowledge, evidence was also obtained of the photoformation of potentially toxic and/or mutagenic nitroaromatic compounds upon irradiation of natural lake water and groundwater samples, proportionally to the nitrate levels.     

Bisphenol A mineralization by integrated ultrasound-UV-iron (II) treatment

Bisphenol A (BPA), an organic compound largely used in the plastic industry as a monomer for production of epoxy resins and polycarbonate, is an emerging contaminant that is released in the environmentfrom bottles and packaging. BPA degradation (118 micromol L(-1)) under sonochemical conditions was investigated in this study, using a 300 kHz frequency, with a 80 W electrical power. Under these conditions, BPA was eliminated by the ultrasound process (-90 min). However, even after long ultrasound irradiation periods (10 h), more than 50% of chemical oxygen demand (COD) and 80% of total organic carbon (TOC) remained in the solution, indicating that most BPA intermediates are recalcitrant toward ultrasonic action. Accumulation of hydrogen peroxide from *OH and *OOH radical recombination was also observed. To increase the efficiency of BPA treatment, experiments combined ultrasound with Fe2+ (100 micromol L(-1)) and/or UV radiation (254 nm): Ultrasound/UV; Ultrasound/Fe2+; Ultrasound/UV/ Fe2+. Both UV and Fe2+ induced hydrogen peroxide dissociation, leading to additional *OH radicals and complete COD and TOC removal. Thus difficulties in obtaining mineralization of micropollutants like BPA through ultrasonic action alone, can be overcome by the Ultrasound/UV/ Fe2+ combination. Moreover, this technique was found to be the most cost-effective one. So, the integrated ultrasound-UV-iron(ll) process was shown to be of interest for the treatment of wastewaters contaminated with BPA.     

Anchored oxygen-donor coordination to iron for photodegradation of organic pollutants

A photocatalyst of oxygen-donor coordination to iron, complex of 5-sulfosalicylic acid (SSA) with ferric ion, supported on resin to cycle Fe3+/Fe2+ center under visible irradiation can effectively generate *OH radicals from H2O2, leading to degradation of organic pollutants in water. The higher turnover number was achieved by this catalyst for the degradation of model compound than those reported for the general N-donor ligands catalysts. The reversible "on/ off" switching of Fe3+/Fe2+ complexation with SSA, coupled with the phenol/phenoxyl radical conversion of the o-phenoxyl moiety of SSA, produces an ideal catalytic system that separates the Fenton reaction and the followed oxidations by *OH radicals (in water phase) from the regeneration of the catalytic species, Fe (SSA)2-, which occurs on the surface of resin. This system not only inhibits the undesired destruction of the ligands by *OH radicals, improving the stability of the catalyst, but also avoids the unnecessary decomposition of H2O2 into HO2* that occurs in the homogeneous Fenton system. Therefore, the system suggests an efficient utilization of H2O2 for degradation of organic pollutants.     

UV photolysis of trichloroethylene: product study and kinetic modeling

Direct UV photolysis of trichloroethylene (TCE) in dilute aqueous solution generated chloride ions as a major end product and several reaction intermediates, such as formic acid, di- and monochloroacetic acids, glyoxylic acid, and, to a lesser extent, mono- and dichloroacetylene, formaldehyde, dichloroacetaldehyde, and oxalic acid. Under prolonged irradiation, these byproducts underwent photolysis, and a high degree of mineralization (approximately 95%) was achieved. TCE decays through the following major pathways: (1) TCE + h nu --> ClCH=C*Cl + Cl*; (2) TCE (H2O) + h nu --> ClCH(OH)-CHCl2; (3) TCE + h nu --> HC[triple bond]CCl + Cl2; (4) TCE + h nu --> ClC[triple bond]CCl + HCl; (5) TCE + Cl* --> Cl2HC-C*Cl2. A kinetic model was developed to simulate the destruction of TCE and the formation and fate of byproducts in aqueous solution under irradiation with polychromatic light. By fitting the experimental data, the quantum yields for the four photolysis steps were predicted as phi(1) = 0.13, phi(2) = 0.1, phi(3) = 0.032, and phi(4) = 0.092, respectively. The reaction mechanism proposed for the photodegradation of TCE accounts for all intermediates that were detected. The agreement between the computed and experimental patterns of TCE and reaction products is satisfactory given the complexity of the reaction mechanism and the lack of photolytic kinetic parameters that are provided in the literature.     

Visible-light-assisted degradation of dye pollutants over Fe(III)-loaded resin in the presence of H2O2 at neutral pH values

A novel catalyst was synthesized by direct exchange of ferric ions onto a cationic resin (Amberlite IRA200). Upon visible light irradiation (lambda > 420 nm) in the presence of H2O2, this catalyst was found to be highly effective for the degradation of nonbiodegradable cationic dyes, Malachite green, Rhodamine B, and Methylene blue, even at neutral pH values. It was also easy to separate from the degraded solution. By total organic carbon, FT-IR, and GC-MS analysis, the degradation process of Malachite green was shown to proceed with demethylation and phenyl ring openings into CO2 and small molecular compounds. EPR studies revealed that *OH radicals, other than *OOH/O2*-, were involved as the active species. A possible reaction mechanism is proposed on the basis of all the information obtained under various experimental conditions.     

Electron-beam treatment of aromatic hydrocarbons that can be air-stripped from contaminated groundwater. 1. Model studies in aqueous solution

As a model for the electron-beam degradation of volatile aromatics (benzene, toluene, ethylbenzene, xylenes, BTEX) in groundwater strip gas, to be reported in Part 2, the gamma-radiolysis of benzene has been studied in aqueous solutions. Addition of *OH to the aromatic ring gives rise to hydroxycyclohexadienyl radicals which either dimerize or disproportionate. The various dimers undergo acid-catalyzed water elimination yielding biphenyl. Phenol is formed upon disproportionation directly, but also via dihydroxycyclohexadiene which subsequently undergoes acid-catalyzed water elimination. Co-radiolysis of benzene with nitrite generates *NO2 in addition to the hydroxycyclohexadienyl radical. These not only interact with one another (product: nitrobenzene via nitro-hydroxycyclohexadienes) but the *NO2 radical is also capable of abstracting cyclohexadienylic hydrogens. This reaction leads to the formation of 2- and 4-nitrophenol and to further nitrated products that were not identified. These are suggested to be formed in an analogous reaction of *NO2 with the hydroxycylohexadienyl dimers. The effect of O2 on these reactions and the relevance for the gas-phase radiolysis of BTEX is discussed.     

桑葚多糖超声提取、脱色工艺优化及其抗氧化活性分析

本文研究桑葚多糖超声提取工艺、树脂脱色工艺和体外抗氧化活性。以桑葚粗多糖得率为指标,通过单因素实验、正交试验考察超声提取温度、料液比、超声时间、超声功率的影响;以脱色率为指标,通过单因素实验、正交试验考察脱色时间、多糖溶液浓度、脱色温度的影响;通过ABTS法、DPPH法、邻二氮菲法、邻苯三酚法考察其抗氧化能力。结果表明,超声提取桑葚多糖的最佳工艺为:超声温度50 ℃、料液比1:30 g/mL、超声时间70 min、超声功率500 W,该条件下多糖得率为4.59%±0.25%;AB-8大孔吸附树脂脱色的最佳工艺为:脱色时间5 h、桑葚粗多糖溶液浓度4 mg/mL、脱色温度25 ℃,该条件下脱色率为62.34%±1.27%;桑葚多糖清除ABTS+自由基、DPPH自由基、羟基自由基和超氧阴离子自由基的IC₅₀分别为0.14、0.68、0.19和3.14 mg/mL。     

Efficient destruction of pathogenic bacteria with NiO/SrBi2O4 under visible light irradiation

The photocatalytic inactivation of pathogenic bacteria in water was investigated systematically with NiO/SrBi2O4 under visible light (lambda > 420 nm) irradiation. The catalyst was found to be highly effective in killing Escherichia coli, a Gram-negative bacterium, and Staphylococcus aureus, a Gram-positive bacterium. ESR studies revealed that *OH and O2*- were involved as the active species in the photocatalytic reaction. The decomposition process of the cell wall and the cell membrane was directly observed byTEM and further confirmed by the determination of potassium ion (K+) leakage from the killed bacteria. A possible cell damage mechanism by visible-light-driven NiO/SrBi2O4 is proposed. In addition, the effects of pH, methanol, and inorganic ions on bacterial photocatalytic inactivation were investigated. These results indicated that the electrostatic force interaction of bacteria-catalyst is crucial for high bactericidal efficiency.     

Free radical chemistry of disinfection byproducts. 2. Rate constants and degradation mechanisms of trichloronitromethane (chloropicrin)

Absolute rate constants for the free-radical-induced degradation of trichloronitromethane (TCNM, chloropicrin) were determined using electron pulse radiolysis and transient absorption spectroscopy. Rate constants for hydroxyl radical, *OH, and hydrated electron, e(aq)-, reactions were (4.97 +/- 0.28) x 10(7) M(-1) s(-1) and (2.13 +/- 0.03) x 10(10) M(-1) s(-1), respectively. It appears that the *OH adds to the nitro-group, while the e(aq)- reacts via dissociative electron attachment to give two carbon centered radicals. The mechanisms of these free radical reactions with TCNM were investigated, using 60Co gamma irradiation at various absorbed doses, measuring the disappearance of TCNM and the appearance of the product nitrate and chloride ions. The rate constants and mechanistic data were combined in a kinetic computer model that was used to describe the major free radical pathways for the destruction of TCNM in solution. These data are applicable to other advanced oxidation/reduction processes.     

Kinetics and products of photolysis and reaction with OH radicals of a series of aromatic carbonyl compounds

We have investigated the photolysis and OH radical reactions of phthaldialdehyde, 2-acetylbenzaldehyde, and 1,2diacetylbenzene, atmospheric reaction products of naphthalene and alkylnaphthalenes, and of phthalide, a photolysis product of phthaldialdehyde. Using a relative rate method with 1,2,4-trimethylbenzene and 2,2,3,3-tetramethylbutane as reference compounds, measured rate constants for the gas-phase OH radical reactions (in units of 10(-12) cm3 molecule(-1) s(-1)) were as follows: phthaldialdehyde, 23 +/- 3; 2-acetylbenzaldehyde, 17 +/- 3; 1,2-diacetylbenzene, < 1.2; and phthalide, < 0.8. Blacklamp irradiation showed that phthaldialdehyde and 2-acetylbenzaldehyde photolyze, and, combined with absorption spectra measured in n-hexane solution, average photolysis quantum yields of 0.19 and 0.21, respectively, were derived (290-400 nm). No evidence for photolysis of 1,2-diacetylbenzene or phthalide by blacklamps was obtained. The major atmospheric loss process of phthaldialdehyde and 2-acetylbenzaldehyde are estimated to be by photolysis, with photolysis lifetimes of 1.4-1.5 h for a 12-hr average NO2 photolysis rate of 0.312 min(-1). Phthalic anhydride was the major observed product from the OH radical-initiated reactions of all four compounds and was also formed from photolysis of phthaldialdehyde and 2-acetylbenzaldehyde. The major photolysis products observed were phthalide from phthaldialdehyde and 3-methylphthalide from 2-acetylbenzaldehyde.     

Ionizing radiation-induced destruction of benzene and dienes in aqueous media

Pulse radiolysis with spectrophotometric and conductometric detection was utilized to study the formation and reactions of radicals from benzene and dienes in aqueous solutions. The benzene OH adduct, *C6H6OH, reacts with O2 (k = 3 x 10(8) L mol(-1) s(-1)) in a reversible reaction. The peroxyl radical, HOC6H6O2*, undergoes O2*- elimination, bimolecular decay, and reaction with benzene to initiate a chain reaction, depending on the dose rate, benzene concentration, and pH. The occurrence of the chain reaction is demonstrated in low-dose-rate gamma radiolysis experiments where the consumption of O2 was monitored. 1,4-Cyclohexadiene, 1,4-hexadiene, and 1,4-pentadiene form OH-adducts and undergo H-abstraction by O*- radicals. The OH-adducts react with O2 to form peroxyl radicals. These peroxyl radicals, however, do not undergo unimolecular O2*- elimination but rather decay by second-order processes, which lead to subsequent steps of O2*- elimination.     

Photoinduced oxidation of Hg0(aq) in the waters from the St. Lawrence estuary

The oxidation of volatile aqueous Hg0 in aquatic systems may be important in decreasing the fluxes of Hg out of the water column. Using incubations of natural samples from the St. Lawrence River, we examined some of the parameters that control this oxidation. Hg0 was found to be chiefly mediated by UV radiation since (i) "dark" oxidation was not found to be statistically significant; (ii) visible light induced a significant but slow photooxidation (k = 0.09 h(-1)); and (iii) visible + UV radiation led to a faster photooxidation (k = 0.6-0.7 h(-1)), mainly because of UV-A induced reactions. Doubling UV irradiation did not increase the reaction rate of Hg0 photooxidation in natural water samples, indicating that some factor other than photon flux was rate limiting and suggesting that the reaction involves intermediate photoproduced oxidant(s). The addition of methanol, a *OH scavenger, decreased Hg photooxidation rates by 25% in brackish waters and by 19% in artificial saline water containing semiquinones, indicating that *OH may be partly responsible for Hg0 oxidation. Photooxidation rates were not affected by oxygen concentrations and did not decrease when samples were heat-sterilized, treated with chloroform, or filtered prior to exposure to light.     

The ROH,UV concept to characterize and the model uv/H202 process in natural waters

A new concept is introduced to characterize and model the UV/H2O2 advanced oxidation process (AOP) in water. Similarto the Rct concept used to describe OH radical exposure per ozone dose, the ROH,UV concept is defined as the experimentally determined *OH radical exposure per UV fluence. ROH,UV was determined by examining the destruction of a probe compound, para-chlorobenzoic acid in four different waters: DI water and three natural waters. ROH,UV was found to be affected greatly by water quality, specifically background *OH radical scavenging, which competed forthe formed *OH radical with the probe compound, and background UV absorbance, which screened UV irradiation from the hydrogen peroxide. The ROH,UV values determined in the experiments using low-pressure Hg lamp were greater than those for the medium-pressure Hg lamp . Finally, the ROH,UV concept was utilized to calculate an overall scavenging factor for each water matrix, and this was successfully utilized in conjunction with the steady-state *OH radical model to improve the prediction of the oxidation of endocrine-disrupting compounds 17-alpha-ethinyl estradiol and 17-beta-estradiol in the natural waters.