Oxidation of TNT by photo-Fenton process

A series of photo-Fenton reactions have been performed for the degradation of 2,4,6-trinitrotoluene (TNT) in a 4.2-l reactor. The degradation reaction rate of TNT followed a pseudo-first-order behavior; and the rate constants for 2.4mW cm(-2)UV only, 2.4mW cm(-2)UV/H(2)O(2), Fenton, photo-Fenton (2.4mW cm(-2)) and photo-Fenton (4.7mW cm(-2)) were 0.002min(-1), 0.007min(-1), 0.014min(-1), 0.025min(-1) and 0.037min(-1), respectively. Increasing the intensity of UV light, and the concentrations of ferrous ions and hydrogen peroxide promoted the oxidation rate under the experimental conditions in this study. The weighting factor (f), the Fe(II)-promoted efficiency (r) and the promoted-UV light efficiency (p) were calculated to clarify their effects on the TNT oxidation. Moreover, the inhibition effect of hydroxyl radical was also observed in both Fenton and photo-Fenton oxidation when the concentration of Fe(II) were higher than 2.88mM. Solid phase micro-extraction was first applied to the separation of the organic byproducts from TNT oxidation. GC/MS was employed to identify the byproducts during the Fenton and photo-Fenton oxidation of TNT. These compounds were clarified as 1,3,5-trinitrobenzene, 1-methyl-2,4-dinitrobenzene 2,5-dinitrobenzoic acid and 1,3-dinitrobenzene. By these byproducts, the mechanisms of the methyl group oxidation, decarboxylation, aromatic ring breakage, and hydrolysis can be recognized and demonstrated. The pathway of TNT oxidation by photo-Fenton process was also proposed in this study.     

Synergy of ozonation and photocatalysis to mineralize low concentration 2,4-dichlorophenoxyacetic acid in aqueous solution

Concentration of 2,4-dichlorophenoxyacetic acid (2,4-D) may affect its degradation kinetics in advanced oxidation systems, and combinations of two or more systems can be more effective for its mineralization at low concentration levels. Degradations and mineralizations of 0.045mM 2,4-D using O(3), O(3)/UV, UV/TiO(2) and O(3)/UV/TiO(2) systems were compared, and influence of reaction temperature on the mineralization in O(3)/UV/TiO(2) system was investigated. 2,4-D degradations by O(3), O(3)/UV and UV/TiO(2) systems were similar to the results of earlier investigations with higher 2,4-D concentrations. The degradations and total organic carbon (TOC) removals in the four systems were well described by the first-order reaction kinetics. The degradation and removal were greatly enhanced in O(3)/UV/TiO(2) system, and further enhancements were observed with larger O(3) supplies. The enhancements were attributed to hydroxyl radical (()OH) generation from more than one reaction pathway. The degradation and removal in O(3)/UV/TiO(2) system were very efficient with reaction temperature fixed at 20 degrees C. It was suspected that reaction temperature might have influenced ()OH generation in the system, which needs further attention.     

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.     

Biodegradability and toxicity assessment of trans-chlordane photochemical treatment

The removal of trans-chlordane (C(10)H(6)Cl(8)) from aqueous solutions was studied using UV, UV/H(2)O(2), UV/H(2)O(2)/Fe(2+), UV/TiO(2), or UV/TiO(2)/H(2)O(2) treatment using either UV/Vis blue lamps or UVC lamps (254 nm). H(2)O(2), FeSO(4) and TiO(2) were added at 1700, 456, and 2500 mgL(-1), respectively. trans-Chlordane was not significantly removed in non-irradiated controls and in samples irradiated with UV/Vis. It was also not removed in the absence of surfactant Triton X-114 added at 250 mgL(-1). In the presence of the surfactant, trans-chlordane concentration was reduced by 95-100% after 48 h of UVC and UVC/H(2)O(2) treatments and 70-80% after UVC/H(2)O(2)/Fe(2+), UVC/TiO(2) and UVC/H(2)O(2)/TiO(2) treatments. Based on these results, UVC, UVC/H(2)O(2) and UVC/TiO(2) treatments were further investigated. UVC treatment supported the highest pollutant removal (100% in 48 h), dechlorination efficiency (81% in 48 h), and detoxification to Lepidium sativum seed germination and activated sludge respiration although irradiated samples remained toxic to Chlorella vulgaris. Biodegradation of the UVC irradiated samples removed the source of algae toxicity but this could not be clearly attributed to the removal of trans-chlordane photoproducts because the surfactant interfered with the chemical and biological assays. Evidence was found that trans-chlordane was photodegraded through photolysis causing its successive dechlorination. trans-Chlordane removal was well described by a first order kinetic model at a rate of 0.21±0.01h(-1) at the 95% confidence interval.     

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.     

Photo-oxidation of cork manufacturing wastewater

Several photo-activated processes have been investigated for oxidation of a cork manufacturing wastewater. A comparative activity study is made between different homogeneous (H2O2/UV-Vis and H2O2/Fe2+/UV-Vis) and heterogeneous (TiO2/UV-Vis and TiO2/H2O2/UV-Vis) systems, with degradation performances being evaluated in terms of total organic carbon (TOC) removal. Results obtained in a batch photo-reactor show that photo-catalysis with TiO2 is not suitable for this kind of wastewater while the H2O2/UV-Vis oxidation process, for which the effect of some operating conditions was investigated, allows to remove 39% of TOC after 4 h of operation (for C(H2O2)=0.59 M, pH=10 and T=35 degrees C). The combined photo-activated process, i.e., using both TiO2 and H2O2, yields an overall TOC decrease of 46% (for C(TiO2)=1.0 gl(-1)). The photo-Fenton process proved to be the most efficient, proceeds at a much higher oxidation rate and allows to achieve 66% mineralization in just 10 min of reaction time (for C(H2O2)=0.31 M, T=30 degrees C, Fe2+:H2O2=0.12 (mol) and pH=3.2).     

Effect of the carbon coating in Fe-C-TiO(2) photocatalyst on phenol decomposition under UV irradiation via photo-Fenton process

Fe-C-TiO(2) photocatalysts which contained the residue carbon (0.2-3.3 mass%) were prepared from a mixture of TiO(2) and FeC(2)O(4) through the heating at 673-1173 K in Ar. These photocatalysts did not show a high adsorption of phenol, but they were active in photo-Fenton reactions during decomposition of phenol under UV irradiation with addition of H(2)O(2). It was proved that Fe(2+) governed the photoactivity of Fe-C-TiO(2) photocatalysts, it decreased with heat-treatment temperature above 773 K. For comparison, Fe-TiO(2) photocatalyst was prepared by heating TiO(2) and FeC(2)O(4) at 823 K in air for 3h. Phenol decomposition was going much slower on Fe-TiO(2) photocatalyst in comparison with Fe-C-TiO(2), of which mechanism was different, on the former phenol was decomposed by the radical reaction, on the latter through a complex reaction with iron and intermediates of phenol decomposition. Therefore carbon-coating TiO(2) was found to be advantageous for mounting iron and its application for the phenol decomposition via photo-Fenton process.     

Comparison of the degradation of p-hydroxybenzoic acid in aqueous solution by several oxidation processes

A comparative study is made of 12 methods of chemical oxidation applied to degrading p-hydroxybenzoic acid in aqueous solution. The oxidation processes tested were: UV, O3, UV/TiO2, O3/Fe2+, O3/H2O2, O3/UV, UV/H2O2, H2O2/Fe2+, H2O2/Fe2+/O3, UV/H2O2/O3, H2O2/Fe2+/UV and O3/UV/H2O2/Fe2+. The 12 processes were ranked by reactivity. In a kinetic study, the overall kinetic rate constant was split up into three components: direct oxidation by UV irradiation (photolysis), direct oxidation by ozone (ozonation), and oxidation by free radicals (mainly OH*).     

不同高级氧化法对水中低浓度药物甲硝唑降解过程的比较

采用UV、H₂O₂、UV/H₂O₂、Fenton、UV/Fenton和UV/TiO₂方法,对水中低浓度的药物甲硝唑进行降解。通过HPLC和UV-Vis光谱得到的甲硝唑去除率。详细讨论了Fe²⁺、TiO₂和H₂O₂的初始浓度以及溶液的初始pH值对降解效率的影响。结果表明,UV/Fenton和UV/TiO₂ 2种系统对水中低浓度甲硝唑均有很好的去除效果,但前者的光催化效率更高。在甲硝唑浓度=6 μmol/L,H₂O₂和Fe²⁺的初始浓度分别为0.5 mg/L和2.94 μmol/L,pH=4的条件下,UV/Fenton方法对甲硝唑水溶液光催化的最佳效率为95.8%。     

Photochemical degradation and mineralization of 4-chlorophenol

INTENTION, GOAL, SCOPE, BACKGROUND: Since the intermediate products of some compounds can be more toxic and/or refractory than the original compund itself, the development of innovative oxidation technologies which are capable of transforming such compounds into harmless end products, is gaining more importance every day. Advanced oxidation processes are one of these technologies. However, it is necessary to optimize the reaction conditions for these technologies in order to be cost-effective. OBJECTIVE: The main objectives of this study were to see if complete mineralization of 4-chlorophenol with AOPs was possible using low pressure mercury vapour lamps, to make a comparison of different AOPs, to observe the effect of the existence of other ions on degradation efficiency and to optimize reaction conditions. METHODS: In this study, photochemical advanced oxidation processes (AOPs) utilizing the combinations of UV, UV/H2O2 and UV/H2O2/Fe2+ (photo-Fenton process) were investigated in labscale experiments for the degradation and mineralization of 4-chlorophenol. Evaluations were based on the reduction of 4-chlorophenol and total organic carbon. The major parameters investigated were the initial 4-chlorophenol concentration, pH, hydrogen peroxide and iron doses and the effect of the presence of radical scavengers. RESULTS AND DISCUSSION: It was observed that the 4-chlorophenol degradation efficiency decreased with increasing concentration and was independent of the initial solution pH in the UV process. 4-chlorophenol oxidation efficiency for an initial concentration of 100 mgl(-1) was around 89% after 300 min of irradiation in the UV process and no mineralization was achieved. The efficiency increased to > 99% with the UV/H2O2 process in 60 min of irradiation, although mineralization efficiency was still around 75% after 300 min of reaction time. Although the H2O2/4-CP molar ratio was kept constant, increasing initial 4-chlorophenol concentration decreased the treatment efficiency. It was observed that basic pHs were favourable in the UV/H2O2 process. The results showed that the photo-Fenton process was the most effective treatment process under acidic conditions. Complete disappearance of 100 mgl(-1) of 4-chlorophenol was achieved in 2.5 min and almost complete mineralization (96%) was also possible after only 45 min of irradiation. The efficiency was negatively affected from H2O2 in the UV/H2O2 process and Fe2+ in the photo-Fenton process over a certain concentration. The highest negative effect was observed with solutions containing PO4 triple ions. Required reaction times for complete disappearance of 100 mgl(-1) 4-chlorophenol increased from 2.5 min for an ion-free solution to 30 min for solutions containing 100 mgl(-1) PO4 triple ion and from 45 min to more than 240 min for complete mineralization. The photodegradation of 4-chlorophenol was found to follow the first-order law. CONCLUSION: The results of this study showed that UV irradiation alone can degrade 4-CP, although at very slow rates, but cannot mineralize the compound. The addition of hydrogen peroxide to the system, the so-called UV/H2O2 process, significantly enhances the 4-CP degradation rate, but still requires relatively long reaction periods for complete mineralization. The photo-Fenton process, the combination of homogeneous systems of UV/H2O2/Fe2+ compounds, produces the highest photochemical elimination rate of 4-CP and complete mineralization is possible to achieve in quite shorter reaction periods when compared with the UV/H2O2 process. RECOMMENDATIONS AND OUTLOOK: It is more cost effective to use these processes for only purposes such as toxicity reduction, enhancement of biodegradability, decolorization and micropollutant removal. However the most important point is the optimization of the reaction conditions for the process of concern. In such a case, AOPs can be used in combination with a biological treatment systems as a pre- or post treatment unit providing the cheapest treatment option. The AOP applied, for instance, can be used for toxicity reduction and the biological unit for chemical oxygen demand (COD) removal.     

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).     

Degradation of polychlorinated dibenzo-p-dioxins in aqueous solution by Fe(II)/H2O2/UV system

The photodegradation of polychlorinated dibenzo-p-dioxins (PCDDs), which include tetra- to octa-CDDs (TeCDD, PeCDD, HxCDD, HpCDD and OCDD), was carried out in the presence of Fe(II) and H2O2 mixed reagent. The degradation efficiency was strongly influenced by UV irradiation, and the initial concentrations of H2O2 and Fe(II). An initial TeCDD concentration of 10 ng l(-1) was completely degraded within 20 min under the optimum conditions. All PCDDs tested were successfully degraded by Fe(II)/H2O2/UV treatment and complete degradation of TeCDD, PeCDD and HxCDD was achieved within 120 min. PCDD photodegradation rates decreased with the number of chlorine atoms. The degradation process of TeCDD by this system seems to be initiated by an oxidative reaction (OH* radical attack) because less chlorinated DDs as intermediate products were not detected. From the Frontier electron density calculation, the first OH* radical attack positions on TeCDD were found to be four C atoms neighboring two O atoms. The decomposition of TeCDD gave 4,5-dichlorocatechol as an intermediate product. A TeCDD degradation scheme was proposed based on the identified intermediate and the values of Frontier electron density. Based on these results, Fe(II)/H2O2/UV system could be useful technology for the treatment of wastewater containing persistent pollutants such as dioxins and polychlorinated biphenyls.     

Chemical absorption process for degradation of VOC gas using heterogeneous gas-liquid photocatalytic oxidation: toluene degradation by photo-Fenton reaction

A novel process for degradation of toluene in the gas-phase using heterogeneous gas-liquid photocatalytic oxidation has been developed. The degradation of toluene gas by photo-Fenton reaction in the liquid-phase has experimentally examined. The photo-Fenton reaction in the liquid-phase could improve the overall toluene absorption rate by increasing the driving force for mass transfer and as a result enhance the removal of toluene in the exhaust gas. The toluene concentrations in the inlet gas were varied in the range from 0.0968 to 8.69gm(-3) with initial hydrogen peroxide concentration of 400mgl(-1) and Fe dose of 5.0mgl(-1). It was found that toluene in the inlet gas was almost completely dissolved into water and degraded in the liquid-phase for the inlet toluene gas concentration of less than 0.42gm(-3). The dynamic process of toluene gas degradation by the photo-Fenton reaction providing information for reaction kinetics and mass transfer rate was examined. Toluene removal kinetic analysis indicated that photo-Fenton degradation was significantly affected by H(2)O(2) concentration. The experimental results were satisfactorily described by the predictions simulated using the simplified tanks-in-series model combined with toluene removal kinetic analysis. The present results showed that the proposed chemical absorption process using the photo-Fenton heterogeneous gas-liquid photocatalytic oxidation is very effective for degradation of volatile organic gases.     

Degradation of the pharmaceutical metronidazole via UV, Fenton and photo-Fenton processes

Degradation rates and removal efficiencies of Metronidazole using UV, UV/H2O2, H2O2/Fe2+, and UV/H2O2/Fe2+ were studied in de-ionized water. The four different oxidation processes were compared for the removal kinetics of the antimicrobial pharmaceutical Metronidazole. It was found that the degradation of Metronidazole by UV and UV/H2O2 exhibited pseudo-first order reaction kinetics. By applying H2O2/Fe2+, and UV/H2O2/Fe2+ the degradation kinetics followed a second order behavior. The quantum yields for direct photolysis, measured at 254 nm and 200-400 nm, were 0.0033 and 0.0080 mol E(-1), respectively. Increasing the concentrations of hydrogen peroxide promoted the oxidation rate by UV/ H2O2. Adding more ferrous ions enhanced the oxidation rate for the H2O2/Fe2+ and UV/H2O2/Fe2+ processes. The major advantages and disadvantages of each process and the complexity of comparing the various advanced oxidation processes on an equal basis are discussed.     

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).     

Novel imazethapyr detoxification applying advanced oxidation processes

Different degradation methods have been applied to assess the suitability of advanced oxidation process (AOPs) to promote mineralization of imazethapyr [(RS)-5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid], a widely used imidazolinone class herbicide, the persistence of which has been demonstrated in surface and ground waters destined to human uses. Independent of the oxidation process assessed, the decomposition of imazethapyr always followed a pseudo-first order kinetic. The direct UV-irradiation (UV) of the herbicide as well as its oxidation with ozone (O?), and hydrogen peroxide tied to UV-irradiation (H?O?/UV) were sufficiently slow to permit the identification of intermediate products, the formation pathway of which has been proposed. Ozonation joined to UV-irradiation (O?/UV), ozonation joined to titanium dioxide photo-catalysis (TiO?/UV+O?), sole photo-catalysis (TiO?/UV), and photo-catalysis reinforced with hydrogen peroxide-oxidation (TiO?/UV+H?O?) were characterized by a faster degradation and rapid formation of a lot of small molecules, which were quickly degraded to complete mineralization. The most effective oxidation methods were those using titanium dioxide photo-catalysis enhanced either by ozonation or hydrogen peroxide. Most of all, these last processes were useful to avoid the development of dangerous by-products.     

Degradation of azo dye Procion Red MX-5B by photocatalytic oxidation

The photocatalytic oxidation (PCO) of a monoazo dye Procion Red MX-5B under various physico-chemical conditions was investigated. Degradation of the dye by PCO was enhanced by augmentation in UV intensity, titanium dioxide and hydrogen peroxide concentrations but was inhibited by increase in initial dye concentration. The PCO process was affected by pH in a peculiar way. In the presence of 100 mg/l of TiO2 and the absence of H2O2, the highest reaction rate was observed when the initial pH was 10. With 500 mg/l of TiO2 and 10 mM of H2O2, the reaction was the fastest at initial pH of 3-5. The optimal conditions for the degradation of the dye, at an UV intensity of 17 mW/cm2, were determined to be: TiO2 concentration, 500 mg/l; initial H2O2 concentration, 10 mM; initial pH, 5.0. Monitoring of TOC loss showed that the dye was mineralized by 90% within 80 min under these conditions. Nevertheless, the persistence of a low level of TOC indicated that mineralization was not complete and dead-end product(s) which was (were) resistant to PCO might have accumulated.     

The role of organic ligands in ferrous-induced photochemical degradation of 2,4-dichlorophenoxyacetic acid

Recent studies have shown that hydrogen peroxide is generated in a ferrioxalate-induced photoreductive reaction, but information about the effect of organic ligands on the photochemical behaviour of ferrous species is limited. The degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by a ferrous-catalyzed oxidation in the presence of various ligands such as formate, citrate, malelate, oxalate, and ethylenediaminetetra-acetic acid (EDTA) was studied. The experiments were conducted under either dark or irradiated (350n m) conditions. Forty-two percent and 34% of 2,4-D were removed by the Fe(2+)/oxalate/UV and Fe(2+)/citrate/UV processes, respectively, after 30 min of reaction and oxidative intermediates were obtained in both cases. The presence of hydroxylated intermediates suggests that 2,4-D may be attacked by hydroxyl radicals, which are the products of the photo-Fenton-like reaction. As such, hydrogen peroxide was produced by the photolysis of ferrous oxalate or ferrous citrate, referred to hereafter as photogenerated H(2)O(2). As expected, the total removal percentage of 2,4-D jumped to 97% when 1mM of hydrogen peroxide (so-called spiked H(2)O(2)) was externally added to the reaction vessel to initiate the Fe(2+)/oxalate/UV process. Therefore, the treatment of 2,4-D by the Fe(2+)/oxalate/H(2)O(2)/UV system can be operated in two steps: the photolysis of ferrous oxalate first, followed by adding the spiked H(2)O(2) sometime after the commencement of the reaction. A two-phase model has been developed to describe this tandem ferrous-catalyzed photooxidation, which would help to achieve the mineralization of 2,4-D.     

Fresnel lens to concentrate solar energy for the photocatalytic decoloration and mineralization of orange II in aqueous solution

The decoloration and mineralization of the azo dye orange II under conditions of artificial ultraviolet light and solar energy concentrated by a Fresnel lens in the presence of hydrogen peroxide and TiO(2)-P25 was studied. A comparative study to demonstrate the viability of this solar installation was done to establish if the concentration reached in the focus of the Fresnel lens was enough to improve the photocatalytic degradation reaction. The degradation efficiency was higher when the photolysis was carried out under concentrated solar energy irradiation as compared to UV light source in the presence of an electron acceptor such us H(2)O(2) and the catalyst TiO(2). The effect of hydrogen peroxide, pH and catalyst concentration was also determined. The increase of H(2)O(2) concentration until a critical value (14.7 mM) increased both the solar and artificial UV oxidation reaction rate by generating hydroxyl radicals and inhibiting the (e(-)/h(+)) pair recombination, but the excess of hydrogen peroxide decreases the oxidation rate acting as a radical or hole scavenger and reacting with TiO(2) to form peroxo-compounds, contributing to the inhibition of the reaction. The use of the response surface methodology allowed to fit the optimal values of the parameters pH and catalyst concentration leading to the total solar degradation of orange II. The optimal pH range was 4.5-5.5 close to the zero point charge of TiO(2) depending on surface charge of catalyst and dye ionization state. Dosage of catalyst higher than 1.1 gl(-1) decreases the degradation efficiency due to a decrease of light penetration.     

A comparative study of the effects of chloride, sulfate and nitrate ions on the rates of decomposition of H2O2 and organic compounds by Fe(II)/H2O2 and Fe(III)/H2O2

The effects of chloride, nitrate, perchlorate and sulfate ions on the rates of the decomposition of hydrogen peroxide and the oxidation of organic compounds by the Fenton's process have been investigated. Experiments were conducted in a batch reactor, in the dark at pH < or = 3.0 and at 25 degrees C. Data obtained from Fe(II)/H2O2 experiments with [Fe(II)]0/[H2O2]0 > or = 2 mol mol(-1), showed that the rates of reaction between Fe(II) and H2O2 followed the order SO4(2-) > ClO4(-) = NO3- = Cl-. For the Fe(III)/H2O2 process, identical rates were obtained in the presence of nitrate and perchlorate, whereas the presence of sulfate or chloride markedly decreased the rates of decomposition of H2O2 by Fe(III) and the rates of oxidation of atrazine ([atrazine]0 = 0.83 microM), 4-nitrophenol ([4-NP]0 = 1 mM) and acetic acid ([acetic acid]0 = 2 mM). These inhibitory effects have been attributed to a decrease of the rate of generation of hydroxyl radicals resulting from the formation of Fe(III) complexes and the formation of less reactive (SO4(*-)) or much less reactive (Cl2(*-)) inorganic radicals.