Homogeneous degradation of 1,2,9,10-tetrachlorodecane in aqueous solutions using hydrogen peroxide, iron and UV light

The homogeneous degradation of the polychlorinated n-alkane, 1,2,9,10-tetrachlorodecane (T4C10), was studied in aqueous solutions of hydrogen peroxide, including Fenton and photo-Fenton reaction conditions. All solutions were adjusted to a pH of 2.8 and an ionic strength of 0.1 M NaClO4 prior to photolysis. T4C10 (2 x 10(-6) M) was substantially degraded by the H2O2/UV system (1.0 x 10(-2) M H2O2), with 60% disappearance in 20 min of irradiation in a photoreactor equipped with 300 nm lamps of light intensity 3.6 x 10(-5) Ein L(-1) min(-1) (established by ferrioxalate actinometry). The reaction produced stoichiometric amounts of chloride ion indicating complete dechlorination of the chlorinated n-alkane. T4C10 degraded very slowly under Fenton (Fe2+/H2O2/dark) and Fenton-like (Fe3+/H2O2/dark) conditions. However, when the same solutions were irradiated, T4C10 degraded more rapidly than in the H2O2/UV system, with 61% disappearance in 10 min of exposure. The rapid degradation is related to the enhanced degradation of hydrogen peroxide to oxidizing *OH radicals under photo-Fenton conditions. Degradation was inhibited in both the H2O2/UV and photo-Fenton systems by the addition of KI and tert-butyl alcohol due to *OH scavenging.     

Kinetics of oxidation of chlorobenzenes and phenyl-ureas by Fe(II)/H2O2 and Fe(III)/H2O2. Evidence of reduction and oxidation reactions of intermediates by Fe(II) or Fe(III)

The rates of degradation of 1,2,4-trichlorobenzene (TCB), 2,5-dichloronitrobenzene (DCNB), diuron and isoproturon by Fe(II)/H2O2 and Fe(III)/H2O2 have been investigated in dilute aqueous solution ([Organic compound]0 approximately 1 microM, at 25.0 +/- 0.2 degrees C and pH < or = 3). Using the relative rate method with atrazine as the reference compound, and the Fe(II)/H2O2 (with an excess of Fe(II)) and Fe(III)/H2O2 systems as sources of OH radicals, the rate constants for the reaction of OH* with TCB and DCNB were determined as (6.0 +/- 0.3)10(9) and (1.1 +/- 0.2)10(9) M(-1) s(-1). Relative rates of degradation of diuron and isoproturon by Fe(II)/H2O2 were about two times smaller in the absence of dissolved oxygen than in the presence of oxygen. These data indicate that radical intermediates are reduced back to the parent compound by Fe(II) in the absence of oxygen. Oxidation experiments with Fe(III)/H2O2 showed that the rate of decomposition of atrazine markedly increased in the presence of TCB and this increase has been attributed to a regeneration of Fe(II) by oxidation reactions of intermediates (radical species and dihydroxybenzenes) by Fe(III).     

Photooxidation of naphthalenesulfonic acids: comparison between processes based on O(3), O(3)/activated carbon and UV/H(2)O(2)

The aim of the present study was to analyze and compare the efficacy of UV photodegradation with that of different advanced oxidation processes (O(3), UV/H(2)O(2), O(3)/activated carbon) in the degradation of naphthalenesulfonic acids from aqueous solution and to investigate the kinetics and the mechanism involved in these processes. Results obtained showed that photodegradation with UV radiation (254 nm) of 1-naphthalenesulfonic, 1,5-naphthalendisulfonic and 1,3,6-naphthalentrisulfonic acids is not effective. Presence of duroquinone and 4-carboxybenzophenone during UV irradiation (308-410 nm) of the naphthalenesulfonic acids increased the photodegradation rate. Addition of H(2)O(2) during irradiation of naphthalenesulfonic acids accelerated their elimination, due to the generation of ()OH radicals in the medium. Comparison between UV photodegradation 254 m and the advanced oxidation processes (O(3), O(3)/activated carbon and UV/H(2)O(2)) showed the low-efficacy of the former in the degradation of these compounds from aqueous medium. Thus, among the systems studied, those based on the use of UV/H(2)O(2) and O(3)/activated carbon were the most effective in the oxidation of these contaminants from the medium. This is because of the high-reactivity of naphthalenesulfonic acids with the *OH radicals generated by these two systems. This was confirmed by the values of the reaction rate constant of *OH radicals with these compounds k(OH), obtained by competitive kinetics (5.7 x 10(9) M(-1) s(-1), 5.2 x 10(9) M(-1) s(-1) and 3.7 x 10(9) M(-1) s(-1) for NS, NDS and NTS, respectively).     

Comparison of advanced oxidation processes and identification of monuron photodegradation products in aqueous solution

The photodegradation of monuron (3-(4-chlorophenyl)-1,1-dimethylurea) in aqueous solutions under simulated solar irradiation has been conducted by different advanced oxidation processes (UV/H(2)O(2), UV/H(2)O(2)/Fe(2+), UV/H(2)O(2)/TiO(2), UV/TiO(2), dark H(2)O(2)/Fe(3+)). The degradation rates were always higher for the homogeneous catalysis in photo-Fenton reactions (UV/H(2)O(2)/Fe(2+)) compared to the heterogeneous photocatalytic systems (TiO(2)/UV and UV/H(2)O(2)/TiO(2)). Optimal concentrations of Fe(2+) and H(2)O(2) for the abatement of the herbicide in the photo-Fenton system were found to be 1 mM Fe(II) and 10 mM H(2)O(2). Several intermediary products were identified using large volume injection micro-liquid chromatography with UV detection (mu-LC-UV), mu-LC-MS and GC-MS techniques and a degradation mechanism has been proposed.     

Photocatalytic removal of fenitrothion in pure and natural waters by photo-Fenton reaction

The photocatalytic removal kinetics of fenitrothion at a concentration of 0.5mgl(-1) in pure and natural waters were investigated in Fe(III)/H2O2/UV-Vis, Fe(III)/UV-Vis and H2O2/UV-Vis oxidation systems, with respect to decreases in fenitrothion concentrations with irradiation time using a solar simulator. Fenitrothion concentrations were determined by HPLC analysis. Furthermore, total mineralization of fenitrothion in these systems was evaluated by monitoring the decreases in DOC concentrations with solar simulator irradiation time by TOC analysis. It was shown that the degradation rate of fenitrothion was much faster in the Fe(III)/H2O2/UV-Vis system than the Fe(III)/UV-Vis and H2O2/UV-Vis systems in both pure and river waters. Consequently, the mineralization rate of fenitrothion was much faster in the Fe(III)/H2O2/UV-Vis system than in the other two systems. The high *OH generation rate measured in the Fe(III)/H2O2/UV-Vis system was the key to faster degradation of fenitrothion. Increases in the concentrations of H2O2 and Fe led to better final degradation of fenitrothion. These results suggest that the photo-Fenton reaction (Fe(III)/H2O2/UV-Vis) system is likely to be an effective method for removing fenitrothion from contaminated natural waters.     

Half-lives of tetra-, penta-, hexa-, hepta-, and octachlorodibenzo-p-dioxin in rats,monkeys, and humans--a critical review

The elimination half-lives (t1/2) in Sprague-Dawley rats for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 1,2, 3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin (HxCDD), 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (HpCDD) and 1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin (OCDD) were estimated in long-term studies by Schlatter, Poiger and others. Furthermore, there are some published half-lives of TCDD in adult humans. The average half-life of TCDD in adult humans is approximately 2840 days, while in Sprague-Dawley rats the average t1/2 of TCDD is 19 days. The t1/2 of TCDD in humans is about 150 times that of rats. This factor was used to calculate the t1/2 values of the other polychlorinated dibenzo-p-dioxins (PCDDs) in humans from the rat data. Furthermore, the terminal t1/2 values of PCDDs in adult humans were calculated from the regression equation: logt1/2H = 1.34 logt1/2R + 1.25 which was recently established for 50 xenobiotics (t1/2H = terminal half-lives in days for humans, t1/2R = terminal half-lives in days for rats). The following terminal half-lives in adult humans were obtained: 12.6 years for 1,2,3,7,8-PeCDD, 26-45 years for 1,2,3,4,7,8-HxCDD, 80-102 years for 1,2,3,4,6,7,8-HpCDD and ca. 112-132 years for OCDD. These half-lives of PCDDs are critically compared with measured t1/2 values of PCDDs and other persistent organic pollutants in rats, monkeys and humans.     

Temperature dependence of hydroxyl radical formation in the hv/Fe3+/H2O2 and Fe3+/H2O2 systems

The thermal enhancement of the formation of *OH by the hv/Fe(III)/H2O2 system (including the Fe(III)/H2O2 system) was quantitatively investigated with reaction temperatures ranging from 25 to 50 degrees C. A temperature dependent kinetic model for the hv/Fe(III)/H2O2 system, incorporating 12 major reactions with no fitted rate constants or activation energies, was developed, and successfully explained the experimental measurements. Particularly, the thermal enhancement of Fe(OH)2+ photolysis which is the most significant step in the hv/Fe(III)/H2O2 system was effectively explained by two factors; (1) the variation of the Fe(OH)2+ concentration with temperature, and (2) the temperature dependence of the quantum yield for Fe(OH)2+ photolysis (measured activation energy=11.4 kJ mol(-1)). Although in both the hv/Fe(III)/H2O2 and Fe(III)/H2O2 systems, elevated temperatures enhanced the formation of *OH, the thermal enhancement was much higher in the dark Fe(III)/H2O2 system than the hv/Fe(III)/H2O2 system. Furthermore, it was found that the relative thermal enhancement of the formation of *OH in the presence of *OH scavengers (tert-butyl alcohol) was magnified in the Fe(III)/H2O2 system but was not in the hv/Fe(III)/H2O2 system.     

Kinetic and chemical assessment of the UV/H2O2 treatment of antiepileptic drug carbamazepine

The UV/H2O2-induced degradation of carbamazepine, a worldwide used antiepileptic drug, recently found as contaminant in many municipal sewage treatment plant (STP) effluents and other aquatic environments, is investigated. The oxidation treatment caused an effective removal of the drug. At complete abatement of the substrate after 4 min treatment, a 35% value of removed total organic carbon (TOC) was obtained. A kinetic constant of (2.05+/-0.14) x 10(9) lmol(-1)s(-1) was determined for OH radical attack to carbamazepine in the UV/H2O2 process. Preparative TLC of the reaction mixture led to the isolation of acridine-9-carboxaldehyde as a reaction intermediate. HPLC and GC/MS analysis indicated formation of small amounts of acridine, salicylic acid, catechol and anthranilic acid among the reaction products. Under the same reaction conditions, synthetically prepared 10,11-epoxycarbamazepine was easily degraded to acridine as main product, suggesting that this epoxide is a likely intermediate in the oxidative conversion of carbamazepine to acridine. Under sunlight irradiation, carbamazepine in water underwent slow degradation to afford likewise acridine as main product. In view of the mutagenic properties of acridine, these results would raise important issues concerning the possible environmental impact of carbamazepine release through domestic wastewaters and support the importance of prolonged oxidation treatments to ensure complete degradation of aromatic intermediates.     

Fenton试剂协同TiO2光催化降解三氯乙酸及协同机理

为了研究Fenton试剂协同TiO2光催化降解三氯乙酸(TCAA)的反应及其协同机理,在自制的光催化反应装置中分别考察了Fenton、UV/TiO2及Fenton/ UV/TiO2 3个反应对TCAA的降解情况。研究结果表明,在TCAA初始浓度为2.0 mg/L,TiO2用量为1.0 g/L,紫外辐射光源为15 W(λmain=254 nm)的实验条件下,Fenton试剂协同TiO2光催化降解TCAA反应在pH 3~7范围内均有较高的降解率;TCAA 在Fenton、UV/TiO2及Fenton/ UV/TiO2 3个反应中的一级反应速率常数分别为0.0009、0.0131和0.0456 min-1;Fenton试剂与TiO2光催化反应间存在较明显的协同效应,其协同机理主要体现在两个方面:一是紫外光激发Fe(OH)2+和H2O2分解产生更多的·OH,二是Fenton试剂中部分被氧化成的Fe3+可与TiO2表面的光生电子结合被还原为Fe2+,抑制了光生电子与空穴的复合,从而提高了TiO2光催化降解TCAA的效率。     

Photodegradation of polychlorinated dibenzo-p-dioxins and dibenzofurans in aqueous solutions and in organic solvents

Aqueous solutions of selected polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were prepared using a generator column and exposed to UV (300 nm) light in the laboratory and to sunlight in an outdoor environment. In the laboratory, additional exposures were also carried out using 60% acetonitrile/water solutions. At 300 nm di- and tetra PCDDs had higher first-order photodegradation rate constants in 60% acetonitrile/water than in pure water. The solvent effect was reversed for PCDFs. These results may be a reflection of the higher polarity of PCDFs compared to PCDDs. In both the indoor and outdoor exposures photodegradation rates decreased with increasing concentrations of chlorination. However, OCDF exposed to 300 nm light in 60% acetonitrile/water and to sunlight in pure water photodegraded more rapidly than tetra CDF. Photolysis rates in sunlight were considerably slower (t(1/2) of 6.4-23 h) than photolysis rates at 300 nm in the laboratory (t(1/2) of 4.3-680 min), reflecting the lower intensity of sunlight in the 300 nm region of the UV/Vis spectrum. The extent of dechlorination of the PCDDs/PCDFs was less than 20% and reductive dechlorination does not appear to be a major process in the photodegradation of PCDDs/PCDFs in aqueous solutions.     

Comparative study of the oxidation of atrazine and acetone by H2O2/UV, Fe(III)/UV, Fe(iii)/H2O2/UV and Fe(II) or Fe(III)/H2O2

In this study, the rates of degradation of organic compounds by several AOPs (H₂O₂/UV, Fe(III)/UV, Fe(III)/H₂O₂/UV, Fe(II)/H₂O₂ and Fe(III)/H₂O₂) have been compared. Experiments were carried out at pH ≈ 3 (perchloric acid / sodium perchlorate solutions) and with UV reactors equipped with a low-pressure mercury vapour lamp (emission at 253.7 run). The data obtained with atrazine ([Atrazine]_o = 100 μg/L) showed that the rate of degradation of atrazine in very dilute aqueous solution is much more rapid with Fe(III)/UV than with H₂O₂/UV. Photo-Fenton process (Fe(III)/H₂O₂/UV) was found to be more efficient than H₂O₂/UV and Fe(II)/H₂O₂ for the mineralization of acetone ([Acetone]_o = 1 mM).     

Fe(3+)- and Cu(2+)-reduction by phenol derivatives associated with Azure B degradation in Fenton-like reactions

Several phenol derivatives were evaluated regarding their capacities for Fe(3+) and Cu(2+) reduction. Selected compounds were assayed in Fenton-like reactions to degrade Azure B. 3,4-Dihydroxyphenylacetic, 2,5-dihydroxyterephtalic, gallic, chromotropic and 3-hydroxyanthranilic acids were the most efficient reducers of both metallic ions. The reaction system composed of 3-hydroxyanthranilic acid/Fe(3+)/H(2)O(2) was able to degrade Azure B at higher levels than the conventional Fenton reaction (87% and 75% of decolorization after 20min reaction, respectively). Gallic and syringic acids, catechol and vanillin induced Azure B degradations at lower levels as compared with conventional Fenton reaction. Azure B was not degraded in the presence of 10% (v/v) methanol or ethanol, which are OH radical scavengers, confirming the participation of this radical in the degradation reactions. Iron-containing reactions consumed substantially more H(2)O(2) than reactions containing copper. In iron-containing reactions, even the systems that caused a limited degradation of the dye consumed high concentrations of H(2)O(2). On the other hand, the reactions containing Fe(3+), H(2)O(2) and 3-hydroxyanthranilic acid or 3,4-dihydroxyphenylacetic acid were the most efficient on degradation of Azure B and also presented the highest H(2)O(2) consumption. These results indicate that H(2)O(2) consumption occurs even when the dye is not extensively degraded, suggesting that part of the generated OH radicals reacts with the own phenol derivative instead of Azure B.     

光催化降解水体异味物质2-MIB的机理

以水体异味物质2-甲基异莰醇(2-methylisoborneol,2-MIB)为研究对象,在紫外光(λ<380 nm)照射下,探讨TiO2(P25)对2-MIB的光催化降解特性及光化学作用机理。结果表明,UV/TiO2光催化体系可以有效去除水体异味物质2-MIB,紫外光照射60 min,对2-MIB的降解率达95%。同时研究了光催化降解体系介质pH,共存腐殖酸(HA)和过硫酸钾(K2S2O8)对UV/TiO2光催化体系降解2-MIB的影响,发现低浓度HA([HA]≤0.5 mg/L)可以提高2-MIB降解速率,当HA浓度高于0.5 mg/L,2-MIB降解反应受到抑制;同时当加入电子受体K2S2O8后,降解体系中活性物种羟基自由基(.OH)明显增加,提高了TiO2对2-MIB的降解能力。利用苯甲酸荧光光度法和POD-DPD显色法跟踪测定降解过程中羟基自由基(·OH)和过氧化氢(H2O2)的变化,表明光催化反应涉及·OH机理。     

Degradation of sodium 4-dodecylbenzenesulphonate photoinduced by Fe(III) in aqueous solution

The Fe(III)-photoinduced degradation of 4-dodecylbenzenesulphonate (DBS) in aqueous solution was investigated. The mixing of DBS (1 mm) and Fe(III) (1 mm) solutions immediately led to the formation of a precipitate that contained DBS and monomeric Fe(OH)2+, the predominant Fe(III) species. Both species were also present in the supernatant. Irradiation of the supernatant solution resulted in a photoredox process that yielded Fe(II) and *OH radicals. The disappearance of DBS was shown to involve only attack by *OH radicals; the quantum yield of DBS disappearance is similar to the quantum yield of *OH radical formation. A wavelength effect was also observed; the rate of DBS disappearance was higher for shorter wavelength irradiation. Five photoproducts, all containing the benzene sulphonate group, were identified. *OH radicals preferentially abstract hydrogen from the carbon in the alpha position of the aromatic ring. The results show that the Fe(III)-photoinduced degradation of DBS could be used as an alternative method for polluted water treatment.     

Fe-PG紫外光辅助活化H2O2流化床高效降解水杨酸

针对常规光催化技术催化剂回收困难,紫外/双氧水(UV/H₂O₂)技术残余H₂O₂污染严重等问题,采用浸渍法制备了铁负载多孔发泡玻璃(Fe-PG)并将其用于紫外光辅助活化H₂O₂流化床降解水杨酸(SA)。结果表明,在相同实验条件下,Fe-PG紫外光辅助活化H₂O₂(UV/H₂O₂/Fe-PG)流化床工艺对SA的降解率、矿化率和H₂O₂利用率均明显优于UV/H₂O₂工艺;在考虑运行成本的情况下,最佳水力停留时间(HRT)为40 min,最佳H₂O₂投加量为3 mmol∙L⁻¹,最佳Fe-PG膨胀率为30%;UV/H₂O₂/Fe-PG流化床工艺对SA溶液初始质量浓度、pH和盐离子具有很强的耐受性,连续运行30 d后对SA的降解率仍维持在98%以上,矿化率仍高达78.1%。UV/H₂O₂/Fe-PG流化床工艺降解SA的主要活性物质为·OH、O₂^·−和h⁺,降解过程符合一级动力学。以上研究结果可为光催化辅助活化H₂O₂流化床技术实现工程应用提供技术支撑。     

双波长紫外(UV185/UV254)直接光降解有机染料的效能及反应机制

印染废水生化出水中残留的有机染料会导致色度超标,已经成为印染废水处理的一大难题。以双波长紫外(UV₁₈₅/UV₂₅₄)为光源,用于对水中亚甲基蓝(MB)、酸性橙7(AO7)和罗丹明B(RhB)等3种典型有机染料的光降解去除。考察了UV₁₈₅辐照强度、有机染料初始质量浓度和初始pH等参数对3种有机染料降解动力学的影响,并对降解机理进行了探究。结果表明：当UV₁₈₅辐照强度为100%、有机染料初始质量浓度为30 mg·L⁻¹和温度为25 ℃时,光降解60 min后MB、AO7和RhB的去除率分别达到100.0%、99.0%和100.0%,且降解过程均符合伪一级反应动力学模型;UV₂₅₄单波长紫外光辐照对有机染料有部分降解作用,其中对RhB降解的贡献达到了51.1%;UV₁₈₅辐照强度与有机染料表观降解速率常数的关系为线性正相关;间接光降解的主要活性物种为·OH、HO₂·和O₂^·−,其中·OH的贡献最大;UV₁₈₅/UV₂₅₄光降解可破坏有机染料的发色基团和芳香结构。以上研究结果可为新型双波长紫外高级氧化体系的开发及其在印染废水深度处理中的应用提供参考。     

紫外光助O3、H2O2氧化降解炼油废碱水的可行性实验

炼油高浓度有机废碱水是石化行业中很难降解的废水.本实验用光化学氧化技术对其进行了降解研究,比较了紫外光/空气、紫外光/O3、紫外光/空气/H2O2系统的处理效果.结果表明,光化学氧化技术降解此废水是可行的,紫外光可使废水中COD、油、酚的降解率明显提高.当废水中O3的投加量每小时为22 mg/L,或H2O2投加量为1%/L时,UV/O3法与UV/空气/H2O2法的降解效果相近.同时,通过控制O3浓度或H2O2的投加量等条件,可使废水中COD、油、酚和硫化物降解到地方污染物二级排放标准.     

铝易拉罐/Fe (Ⅱ)/O2体系降解对氨基苯胂酸的机理

对氨基苯胂酸是一种常见的有机胂化合物,常作为饲料添加剂用于畜牧业。研究了在酸性条件下（pH2体系降解水中的对氨基苯胂酸的机理。通过对各种实验参数如pH值、Fe（Ⅱ）的浓度、羟基自由基清除剂和气体氛围等条件的考察,发现：在酸性条件下,零价铝发生电子转移,体系中的溶解氧和水得电子生成过氧化氢,在外加Fe（Ⅱ）的条件下,促进了芬顿反应的发生,产生强氧化性的物质（·OH）,实现对对氨基苯胂酸的氧化降解。     

Quantitation of Hydroxyl Radicals from Photolysis of Fe(III)-Citrate Complexes in Aerobic Water (5 pp)

Background For their high photoreactivity, Fe(III)-carboxylate complexes are important sources of H2O2 for some atmospheric and surface waters. Citrate is one kind of carboxylate, which can form complexes with Fe(III). In our previous study, we have applied Fe(III)-citrate complexes to degrade and decolorize dyes in aqueous solutions both under UV light and sunlight. Results have shown that carboxylic acids can promote the photodegradation efficiency. It is indicated that the photolysis of Fe(III)-citrate complexes may cause the formation of some reactive species (e. g. H2O2 and ·OH). This work is attempted to quantify hydroxyl radicals generated in the aqueous solution containing Fe(III)-citrate complexes and to interpret the photoreactivity of Fe(III)-citrate complexes for degrading organic compounds. Methods By using benzene as the scavenger to produce phenol, the photogeneration of ·OH in the aqueous solution containing Fe (III)-citrate complexes was determined by HPLC. Results and Discussion In the aqueous solution containing 60.0/30.0 mM Fe(III)/citrate and 7.0 mM benzene at pH 3.0, 96.66 mM ·OH was produced after irradiation by a 250W metal halide light (l ≥ 313 nm) for 160 minutes. Effects of initial pH value and concentrations of Fe(III) and citrate on ·OH radical generation were all examined. The results show that the greatest photoproduction of ·OH in the aqueous solution (pH ranged from 3.0 to 7.0) was at pH 3.0. The photoproduction of ·OH increased with increasing Fe(III) or citrate concentrations. Conclusion In the aqueous solutions containing Fe(III)-citrate complexes, ·OH radicals were produced after irradiation by a 250W metal halide light. It can be concluded that Fe(III)-citrate complexes are important sources of ·OH radicals for some atmospheric and surface waters. Recommendations and Outlook It is believed that the photolysis of Fe(III)-citrate complexes in the presence of oxygen play an important role in producing ·OH both in atmospheric waters and surface water where high concentrations of ferric ions and citrate ions exist. The photoproduction of ·OH has a high oxidizing potential for the degradation of a wide variety of natural and anthropogenic organic and inorganic substances. We can use this method for toxic organic pollutants such as organic dyes and pesticides.     

Non-degradable triazine substrates of atrazine and cyanuric acid hydrothermally and in supercritical water under the UV-illuminated photocatalytic cooperation

Strong oxidation by titanium dioxide photocatalysis can occur by photodegradation of organic contaminants in air and water. Some endocrine disruptors such as 2,4-dichlorophenoxy acetic acid (;;; ), 2,4-dichlorophenol (;;; ), nonylphenol (; ), bisphenol A (), diethyl phthalate (; ), etc. which can be neither biodegraded by bacteria nor degraded thermally can be degraded by TiO(2) photocatalytic treatment. However, incomplete photomineralization partly occurred, when TiO(2) photocatalytic degradation is employed for the treatment of certain endocrine disruptors. For example, no atrazine pesticide having triazine skeleton can be completely mineralized even by a photocatalytic procedure; the photodegradation of atrazine ultimately stops at the intermediate step of cyanuric acid, which cannot be photodegraded even after long illumination times ().In this study, the decomposition of atrazine and cyanuric acid was carried out with a device combining photocatalytic degradation in supercritical water (scH(2)O) or hydrothermal water (hyH(2)O). Atrazine and cyanuric acid can be degraded by the cooperation of either scH(2)O or hyH(2)O and UV illuminated TiO(2)-photocatalytic dispersed system under the fixed pressure of 23 MPa at 623 K or 683 K in a 120-ml Hastelloy batch reactor. The photocatalytic degradation method under high temperature and pressure has found appropriate for the photocatalytic oxidation of acetic acid and 2-chlorobiphenyl under continuous flow conditions at 160 degrees C and 20 atm (). In addition, the wet peroxide oxidation of PCBs by high temperature and pressure has been reported (). The main aims of this research are following. (i): the degradation of atrazine and cyanuric acid within the scH(2)O or hyH(2)O, (ii) the decomposition of atrazine and cyanuric acid catalyzed by TiO(2) particles under scH(2)O or hyH(2)O, and the synergistic effect for several reactions with TiO(2) and scH(2)O or hyH(2)O, and (iii) the mineralization yield of nitrogen and chlorine atoms concerning the chemical structures of atrazine or cyanuric acid (only nitrogen).