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The photolysis of Fe(III)-pyruvate and Fe(III)-citrate complexes in water produces hydroxyl radicals in the presence of dissolved oxygen, and can promote the oxidation of organic compounds. The photodegradation of glyphosate with Fe(III)-pyruvate and Fe(III)-citrate complexes was investigated under irradiation at λ ≥ 365 nm. The effect of initial concentration of glyphosate, the initial pH value, and the Fe(III)/carboxylate ratio were examined. Upon irradiation of glyphosate aqueous solution with the complexes in the acidic range of natural waters, the bioavailable orthophosphate could be released from degradation of glyphosate. The amount of orthophosphate increased with increasing Fe(III)/carboxylate ratio. [ABSTRACT FROM AUTHOR]

The catalytic efficiency of iron (II, III) oxide to promote Fenton-like reaction was examined by employing Rhodamine B (RhB) as a model compound at neutral pH. Two types of iron (II, III) oxides were used as heterogeneous catalysts and characterized by XRD, Mössbauer spectroscopy, BET surface area, particle size and chemical analyses. The adsorption to the catalyst changed significantly with the pH value and the sorption isotherm was fitted using the Langmuir model for both solids. Both sorption and FTIR results indicated that surface complexation reaction may take place in the system. The variation of oxidation efficiency against H2O2 dosage and amount of exposed surface area per unit volume was evaluated and correlated with the adsorption behavior in the absence of oxidant. The occurrence of optimum amount of H2O2 or of exposed surface area for the effective degradation of RhB could be explained by the scavenging effect of hydroxyl radical by H2O2 or by iron oxide surface. Sorption and decolourization rate of RhB as well as H2O2 decomposition rate were found to be dependent on the surface characteristics of iron oxide. The kinetic oxidation experiments showed that structural FeII content strongly affects the reactivity towards H2O2 decomposition and therefore RhB decolourization. The site density and sorption ability of RhB on surface may also influence the oxidation performance in iron oxide/H2O2 system. The iron (II, III) oxide catalysts exhibited low iron leaching, good structural stability and no loss of performance in second reaction cycle. The sorption on the surface of iron oxide with catalytic oxidation using hydrogen peroxide would be an effective oxidation process for the contaminants. [Copyright &y& Elsevier]

In this work, the photooxidation of bisphenol A (BPA), a suspected endocrine disruptor (ED), in water in the presence of ferric and oxalate ions was investigated in a concentric reactor under a 125W high-pressure mercury lamp (λ365nm). The photooxidation efficiencies were dependent on the pH values and ferric/oxalate concentration ratios (Fe(III)/Ox) in the water, with higher efficiency at pH 3.50±0.05 and Fe(III)/Ox 10.0/120.0μmoll-1. The initial rate of photooxidation increases with increasing the initial concentration of BPA from 2.0 to 5.0mgl-1 while do not change at 5.0 and 10.0mgl-1. However, higher removal efficiency of BPA is archived at lower BPA initial concentration over range of 2.0 to 10.0mgl-1. For 2.0mgl-1 BPA, the initial rate of photooxidation is 0.06mgl-1min-1. By using UV–Vis spectrum and LC–MS techniques, the predominant photooxidation product BPA-o-catechol was identified and the mechanisms for the oxidative degradation were proposed. When BPA reacted with OH radicals, C atoms in 3-position were added with OH radicals followed by O2 peroxidation and HO2 radical escape. Then catechol derivatives were produced. After that, the two H atoms on the hydroxy group were extracted in two individual steps to form intermediates semiquinone radical and o-quinone. The intermediates underwent further oxidation, benzene ring cleavage and decarboxylation, up to mineralization ultimately. [Copyright &y& Elsevier]

In this work, the photooxidation of diethylstilbestrol (DES), a synthetic estrogen, was investigated in a concentric reactor under a 125 W high-pressure mercury lamp (λ⩾365 nm). The photooxidation efficiencies were dependent on the pH values and Fe(III)/oxalate ratios of the system, with higher efficiency at pH 3.50±0.05 and Fe(III)/oxalate ratio 10.0/120.0 μmoll−1. The photooxidation reactions obeyed the law of pseudo-first-order reaction at the concentration over the range of 2.0–10.0 mgl−1 of DES. The photooxidation rates decreased with increasing the initial concentrations of DES. For 2.0 mgl−1 DES, the observed photooxidation rate coefficient (kobs) was 0.00622 min−1. By using GC–MS and LC–MS techniques, the predominant photooxidation products DES-o-catechol ([M]+, m/z 284) and DES-4-semiquinone ([M]−, m/z 267) were respectively identified and the mechanisms for the oxidative degradation were proposed. When DES reacted with OH radicals, C atoms in 3-position were added with OH radicals to produce hydrolyzed DES radical followed by two oxidation pathways: (1) dehydrolyzing to produce DES-4-semiquinone which was oxidized further to DES-4,4′-quinone; (2) undergoing peroxidation by O2 and getting rid of HO2 radical to produce DES-o-catechol. After that, the two H atoms on the hydroxy group of the catechol were extracted in two individual steps to form intermediates semiquinone radical and o-quinone. The catechol intermediates underwent further oxidation, benzene ring cleavage and decarboxylation, up to mineralization ultimately. [Copyright &y& Elsevier]

Abstract: The decolorization of azo dye Orange II using a montmorillonite/H2O2 system and a heterogeneous Fenton system, with montmorillonite KSF as a catalyst, has been studied. A series of experiments were performed to analyze the effects of several variables, including pH, KSF dosage, H2O2 dosage and the initial Orange II concentration. The results revealed that under proper conditions, relatively high decolorization efficiency (more than 90%) could be achieved in only 40min when the initial concentration of Orange II was 20mg/L. Response surface methodology (RSM) was applied with a Box–Behnken design (BBD) of a series of experiments, which showed that, of the range of variables studied, the order of influence is pH>KSF dosage>H2O2 dosage. A mathematical model was established and the optimal conditions were determined by RSM. Sequential experiments showed that KSF, re-used from a former reaction, performed well for 4 further runs. Comparisons between homogeneous and heterogeneous catalytic oxidation showed that unreleased free ferrous iron and structural iron in the KSF particles were responsible for the catalysis of the oxidation of Orange II in the montmorillonite/H2O2 system at pH 4. However, at pH 3, the predominant catalytic iron species was the released free ferrous iron. [Copyright &y& Elsevier]

The effect of chelating agents on the Fenton heterogeneous oxidation rate of pentachlorophenol (PCP) in the presence of magnetite (Fe3O4) was investigated in opened batch reactor at neutral pH. Six kinds of chelating agents (CA) were selected including EDTA, CMCD, oxalate, tartrate, citrate and succinate. The PCP oxidation rate in the Fenton-like system was significantly improved by using chelating agents at neutral pH. This observation was supported by the increased concentration of chloride produced by the degradation of PCP. The enhancement factor of heterogeneous oxidation rate was found to be not correlated with that of dissolved iron amount. However, the propagation of homogeneous reaction by the dissolved iron contributed to the improvement of the whole oxidation rate. In homogeneous Fenton system (dissolved Fe2+ or Fe3+), EDTA-driven Fenton reaction showed the highest oxidation rate, while oxalate seems to be more efficient in heterogeneous Fenton system (Fe3O4). In fact, EDTA can bind more strongly than oxalate to magnetite surface and compete more actively than H2O2 or PCP for the sorption on the surface active sites. Decrease in H2O2 decomposition rate value was observed when EDTA is previously adsorbed on the catalyst surface. The surface mechanism of oxidant with iron sites on the catalyst surface appears to be the rate-determining step in heterogeneous Fenton system. [Copyright &y& Elsevier]

Abstract: The oxidation of pentachlorophenol (PCP) on the surface of magnetite used as heterogeneous catalyst has been investigated under various experimental conditions (initial substrate concentration, H2O2 dose, solid loading and temperature) at neutral pH and correlated with the adsorption behavior. The surface reactivity of magnetite was evaluated by conducting the kinetic study of both H2O2 decomposition and PCP oxidation experiments. The occurrence of the optimum values of H2O2 and magnetite concentrations for the effective degradation of PCP could be explained by the scavenging reactions with H2O2 or iron oxide surface. The surface interactions with PCP in the absence and the presence of oxidant can be well described by Langmuir and Langmuir–Hinshelwood models, respectively. All batch experiments indicate that Fenton-like oxidation of PCP was controlled by surface mechanism reaction and the species compete with each other for adsorption on a fixed number of surface active sites. The apparent degradation rate was dominated by the rate of intrinsic chemical reactions on the oxide surface rather than the rate of mass transfer. Raman analysis suggested that the sorbed PCP was removed form magnetite surface at the first stage of oxidation reaction. The mineralization determined by TOC abatement was completed after 7 d, while total dechlorination was achieved at 4 d treatment time. The first reaction of PCP oxidation should be the dechlorination since 90% of chloride was formed at the first 30h corresponding to the total disappearance of parent compound. All X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Mössbauer spectroscopy and chemical analyses showed that the magnetite catalyst exhibited low iron leaching, good structural stability and no loss of performance in second reaction cycle. [Copyright &y& Elsevier]

In this work, the formation of the inclusion complex of bisphenol Z (1,1-bis(4-hydroxyphenyl)cyclohexane, abbreviated as BPCH) with β-cyclodextrin (β-CD) has been studied, 1:1 inclusion complex can be obtained, the formation constant of the β-CD/BPCH complex is 5.94×103 M−1. The photodegradation behavior of BPCH was investigated under monochromatic UV irradiation (λ =254nm). The photodegradation rate constant of BPCH in aqueous solutions with β-CD showed a 9.0-fold increase, and simultaneously the mineralization of BPCH can be enhanced by β-CD. The influence factors on photodegradation of BPCH were also studied and described in details, such as concentration of β-CD, initial concentration of BPCH, organic solvent and pH. The photodegradation of BPCH in the presence of β-CD includes the direct photolysis and the photooxidation of BPCH during the photochemical process. Some predominant photodegradation products are 4-(2,4,5-trihydroxy-phenyl)-4-(4-hydroxyphenyl) butanoic acid, 5,5-bis(4-hydroxyphenyl)pentanoic acid, meta-hydroxylated BPCH, ortho-hydroxylated BPCH and 4-(1-(4-hydroxyphenyl)pentyl)phenol respectively. The enhancement of photodegradation of BPCH mainly results from moderate inclusion depth of BPCH molecule in the β-CD cavity. This kind of inclusion structure allows BPCH molecule sufficient proximity to secondary hydroxyl groups of the β-CD cavity, and these hydroxyl groups could be activated and converted to hydroxyl radicals under UV irradiation, which can enhance the photooxidation of BPCH. [Copyright &y& Elsevier]

Abstract: Simultaneously photocatalytic reduction of Cr(VI) and oxidation of bisphenol A (BPA) in aqueous solution in the presence of Fe(III)–OH complexes were investigated under a 250W metal halide lamp (λ ≥365nm). Synergy effect of the simultaneous photocatalytic oxidation and reduction of both pollutants was achieved. The effects of initial pH value, initial concentration of BPA, Cr(VI) and Fe(III) were preliminarily investigated. The results showed that both photocatalytic reduction of Cr(VI) and degradation of BPA could occur simultaneously in the Fe(III)/Cr(VI)/BPA ternary system, and the rates of photocatalytic reduction of Cr(VI) and the oxidation of BPA were more rapid at a low pH range of 2.0–3.0. The increase of the initial concentration of Fe(III) was favorable to both photocatalytic reduction of Cr(VI) and oxidation of BPA. The reduction efficiency of Cr(VI) decreased with increasing initial concentrations of Cr(VI) and BPA, but the degradation efficiency of BPA was not changed obviously at different Cr(VI) concentrations. [Copyright &y& Elsevier]