Degradation of atrazine by Fenton and modified Fenton reactions

Study on the efficacy and mechanism of Fe-TiO2 visible heterogeneous Fenton catalytic degradation of atrazine

In order to improve the catalytic activity and recycling performance of heterogeneous Fenton catalyst, a heterogeneous Fenton catalyst Fe/TiO₂ based on TiO₂ supported visible light response was prepared by a simple method using TiO₂ synthesized by sol-gel method as carrier and ferric nitrate as Fe source. It was characterized by SEM, EDX, XRD, UV-vis instruments. The influencing factors of catalytic degradation of atrazine by visible light heterogeneous Fenton of Fe/TiO₂ were studied and the reaction kinetics were fitted. The mineralization degree of atrazine was reflected by the removal rate of TOC. The intermediate products by the degradation of the catalytic system was analyzed and the reaction mechanism of Fe/TiO₂-H₂O₂ visible light system was discussed. The XRD results showed that Fe was highly dispersed on the surface of TiO₂ in the form of α-Fe₂O₃. The Fe/TiO₂ catalyst with heterogeneous Fenton and visible light photocatalytic activity was successfully optimized, forbidden bandwidth of Fe/TiO₂ after Fe supported was narrower, the scope of light absorption red-shifted, the electron-hole pairs were more generated, and there was a significant synergistic effect between the carrier TiO₂ and the supported Fe, which exhibited good oxidation capacity for degradation of 10 mg L^-1 atrazine in pH of 3, the concentration of H₂O₂ was 1.6 mM, and the catalyst was added at 1 g L^-1, achieving over 95% removal efficiency within 30 min, and, in the range of pH 3-7, the degradation rate of the reaction for 30 min can be maintained above 75%, which greatly broadened the range of pH application and had good recycling performance. The degradation process conformed to the quasi-first-order kinetic model. Through LC-MS analyzed, 12 intermediate products were formed during the degradation of atrazine, the final products were all cyanuric acid, and then the triazine ring was mineralized into inorganic substances such as CO₂, H₂O and NO₃^- by oxidation of ·OH, and the possible degradation pathways were inferred.

Removal of atrazine by biochar-supported zero-valent iron catalyzed persulfate oxidation: Reactivity, radical production and transformation pathway

Atrazine is a widely used herbicide whose presence poses a potential threat to agriculture and human living environment. This work studied the degradation performances and mechanisms of zero-valent iron and biochar composite (ZVI/BC) activated persulfate (PS) for atrazine. The results showed that the removal percentage of atrazine reached 73.47% within 30 min. Furthermore, the optimal parameters (175 mg/L ZVI/BC, 2 mM PS and initial pH of 3) were obtained through response surface methodology. Meanwhile, the high atrazine removal percentage (83.77%) was obtained under the optimal conditions. Radical quenching studies and electron spin resonance revealed that active substances produced during PS activation, as well as that SO₄·^- and HO· were dominant active species for the atrazine degradation. According to iron corrosion products and XPS analysis, the reaction mechanism of ZVI/BC-PS system was proposed as that ZVI loaded on the composites further activated PS to produce SO₄·^- and HO· which accompany with the valent changing of iron and finally causing degradation of atrazine. In addition, the degradation pathways of atrazine in ZVI/BC-PS system included dealkylation, alkyl oxidation and dechlorination-hydroxylation by the results of GC-MS and LC-MS. These findings demonstrated that ZVI/BC activated persulfate may be an efficient technique for the degradation of atrazine.

Probing the Migration of Free Radicals in Solid and Liquid Media via Cr(VI) Reduction by High-Energy Electron Beam Irradiation

To probe the migration of free radicals (FRs), the reduction behaviours of hexavalent chromium (Cr(VI)) in water and ice by high-energy electron beam (HEEB) irradiation were investigated. Interestingly, the reductive efficiency (RE) of Cr(VI) in water was appreciably higher than that in ice. Thus, it was proposed that the migration ability of FRs in water is distinctly higher than that in ice, likely because the migration performance of FRs is closely related to the intermolecular distance of water molecules. Furthermore, the RE of Cr(VI) in ice decreased gradually with the distance from the irradiated area, indicating that FRs could migrate in ice and that the migration performance was closely related to the RE. Additionally, FRs (hydrated electrons (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\rm{e}}}_{{\rm{aq}}}^{-}$$\end{document}eaq−) and hydrogen radicals (·H)) generated during the irradiation process played a key role in the reduction of Cr(VI). Hydroxyl radicals (·OH) and H₂O₂ were the dominant negative factors for the reduction because of their oxidizing effects, but these factors could be eliminated by the removal of ·OH. This work reveals the migration performance of FRs in different media for the first time. This result may be useful for basic and applied studies in fields of environmental science related to FRs.

Amicarbazone degradation promoted by ZVI-activated persulfate: study of relevant variables for practical application

Alarming amounts of organic pollutants are being detected in waterbodies due to their ineffective removal by conventional treatment techniques, which warn of the urgent need of developing new technologies for their remediation. In this context, advanced oxidation processes (AOPs), especially those based on Fenton reactions, have proved to be suitable alternatives, due to their efficacy of removing persistent organic compounds. However, the use of ferrous iron in these processes has several operational constraints; to avoid this, an alternative iron source was here investigated: zero-valent-iron (ZVI). A Fenton-like process based on the activation of a recently explored oxidant-persulfate (PS)-with ZVI was applied to degrade an emerging contaminant: Amicarbazone (AMZ). The influence of ZVI size and source, PS/ZVI ratio, pH, UVA radiation, dissolved O₂, and inorganic ions was evaluated in terms of AMZ removal efficiency. So far, this is the first time these parameters are simultaneously investigated, in the same study, to evaluate a ZVI-activated PS process. The radical mechanism was also explored and two radical scavengers were used to determine the identity of major active species taking part in the degradation of AMZ. The degradation efficiency was found to be strongly affected by the ZVI dosage, while positively affected by the PS concentration. The PS/ZVI system enabled AMZ degradation in a wide range of pH, although with a lower efficiency under slightly alkaline conditions. Dissolved O₂ revealed to play an important role in reaction kinetics as well as the presence of inorganic ions. UVA radiation seems to improve the degradation kinetics only in the presence of extra O₂ content. Radicals quenching experiments indicated that both sulfate (SO₄^•-) and hydroxyl (^•OH) radicals contributed to the overall oxidation performance, but SO₄^•- was the dominant oxidative species.

Theoretical and experimental study on the degradation mechanism of atrazine in Fenton oxidation treatment

Water can act as a catalyst to reduce the reaction barrier dramatically.

Atrazine degradation by fungal co-culture enzyme extracts under different soil conditions

This investigation was undertaken to determine the atrazine degradation by fungal enzyme extracts (FEEs) in a clay-loam soil microcosm contaminated at field application rate (5 μg g(-1)) and to study the influence of different soil microcosm conditions, including the effect of soil sterilization, water holding capacity, soil pH and type of FEEs used in atrazine degradation through a 2(4) factorial experimental design. The Trametes maxima-Paecilomyces carneus co-culture extract contained more laccase activity and hydrogen peroxide (H2O2) content (laccase = 18956.0 U mg protein(-1), H2O2 = 6.2 mg L(-1)) than the T. maxima monoculture extract (laccase = 12866.7 U mg protein(-1), H2O2 = 4.0 mg L(-1)). Both extracts were able to degrade atrazine at 100%; however, the T. maxima monoculture extract (0.32 h) achieved a lower half-degradation time than its co-culture with P. carneus (1.2 h). The FEE type (p = 0.03) and soil pH (p = 0.01) significantly affected atrazine degradation. The best degradation rate was achieved by the T. maxima monoculture extract in an acid soil (pH = 4.86). This study demonstrated that both the monoculture extracts of the native strain T. maxima and its co-culture with P. carneus can efficiently and quickly degrade atrazine in clay-loam soils.

An overview on the advanced oxidation processes applied for the treatment of water pollutants defined in the recently launched Directive 2013/39/EU

Environmental pollution is a recognized issue of major concern since a wide range of contaminants has been found in aquatic environment at ngL(-1) to μgL(-1) levels. In the year 2000, a strategy was defined to identify the priority substances concerning aquatic ecosystems, followed by the definition of environmental quality standards (EQS) in 2008. Recently it was launched the Directive 2013/39/EU that updates the water framework policy highlighting the need to develop new water treatment technologies to deal with such problem. This review summarizes the data published in the last decade regarding the application of advanced oxidation processes (AOPs) to treat priority compounds and certain other pollutants defined in this Directive, excluding the inorganic species (cadmium, lead, mercury, nickel and their derivatives). The Directive 2013/39/EU includes several pesticides (aldrin, dichlorodiphenyltrichloroethane, dicofol, dieldrin, endrin, endosulfan, isodrin, heptachlor, lindane, pentachlorophenol, chlorpyrifos, chlorfenvinphos, dichlorvos, atrazine, simazine, terbutryn, diuron, isoproturon, trifluralin, cypermethrin, alachlor), solvents (dichloromethane, dichloroethane, trichloromethane and carbon tetrachloride), perfluorooctane sulfonic acid and its derivatives (PFOS), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), nonylphenol and octylphenol, as well as the three compounds included in the recommendation for the first watch list of substances (diclofenac, 17-alpha-ethinylestradiol (EE2) and 17-beta-estradiol (E2)). Some particular pesticides (aclonifen, bifenox, cybutryne, quinoxyfen), organotin compounds (tributyltin), dioxins and dioxin-like compounds, brominated diphenylethers, hexabromocyclododecanes and di(2-ethylhexyl)phthalate are also defined in this Directive, but studies dealing with AOPs are missing. AOPs are recognized tools to destroy recalcitrant compounds or, at least, to transform them into biodegradable species. Diuron (a phenylurea herbicide) and atrazine (from the triazine chemical class) are the most studied pesticides from Directive 2013/39/EU. Fenton-based processes are the most frequently applied to treat priority compounds in water and their efficiency typically increases with the operating temperature as well as under UV or solar light. Heterogeneous photocatalysis is the second most used treatment to destroy pollutants defined in the Directive. Ozone alone promotes the partial oxidation of pollutants, and an increase in the effluent biodegradability, but complete mineralization of pollutants is difficult. To overcome this drawback, ozonation has been combined with heterogeneous catalysts, addition of H2O2, other AOPs (such as photocatalysis) or membrane technologies.