Degradation of azo dyes in water by Electro-Fenton process

The degradation of the azo dyes azobenzene, p-methyl red and methyl orange in aqueous solution at room temperature has been studied by an advanced electrochemical oxidation process (AEOPs) under potential-controlled electrolysis conditions, using a Pt anode and a carbon felt cathode. The electrochemical production of Fenton's reagent (H₂O₂, Fe²⁺) allows a controlled in situ generation of hydroxyl radicals (^·OH) by simultaneous reduction of dioxygen and ferrous ions on the carbon felt electrode. In turn, hydroxyl radicals react with azo dyes, thus leading to their mineralization into CO₂ and H₂O. The chemical composition of the azo dyes and their degradation products during electrolysis were monitored by high performance liquid chromatography (HPLC). The following degradation products were identified: hydroquinone, 1,4-benzoquinone, pyrocatechol, 4-nitrocatechol, 1,3,5-trihydroxynitrobenzene and p-nitrophenol. Degradation of the initial azo dyes was assessed by the measurement of the chemical oxygen demand (COD). Kinetic analysis of these data showed a pseudo-first order degradation reaction for all azo dyes. A pathway of degradation of azo dyes is proposed. Specifically, the degradation of dyes and intermediates proceeds by oxidation of azo bonds and aromatic ring by hydroxyl radicals. The results display the efficiency of the Electro-Fenton process to degrade organic matter. Electronic Publication     

Microwave and Fenton's reagent oxidation of wastewater

We compared two H₂O₂ oxidation methods for the treatment of industrial wastewater: oxidation using Fenton's reagent [H₂O₂/Fe(II)] and microwave irradiation. Both methods were applied to the treatment of synthetic phenol solutions (100 mg L⁻¹) and of an industrial effluent containing a mixture of ionic and non-ionic surfactants at high load (20 g L⁻¹ of COD). The effects of initial pH, initial H₂O₂ concentration, Fenton catalyst amount and irradiation time were assessed. According to the oxidation of phenol, it has been found that the oxidation by Fenton's reagent is dependent on the pH, contrary to the microwave system, which is not influenced by this parameter. For both systems, a limiting amount of oxidant has been found; above this point the oxidation of phenol is not improved by a further addition of peroxide. The oxidation of the industrial surfactant effluent has only been successful with the Fenton's reagent. In this case, large amounts of ferrous ions are necessary for the precipitation of the ionic surfactants of the effluent, followed by the oxidation of the non-ionic constituents of the solution. Electronic Publication     

UV-C light-enhanced photo-Fenton oxidation of methyl parathion

The photodegradation of aqueous solutions containing 0.2 mM methyl parathion has been studied through the optimization of the [H₂O₂]/[Fe³⁺] ratio in a Fe³⁺/H₂O₂/UV-C flow system of 1.3 L capacity. The decay kinetics and TOC abatement have been analyzed for the experiments performed at pH 3.0 and room temperature. All experiments lead to the total methyl parathion destruction after a few minutes, following a pseudo-first-order decay kinetics. Total mineralization can be reached after 120 min at the optimum ratio found, due to the synergistic effect of the very oxidizing hydroxyl radical (^·OH) produced via the Fenton reagent and the effective photodecarboxylation at 253.7 nm.     

Coupled electrocoagulation–electro-Fenton for efficient domestic wastewater treatment

This article reports the first use of coupled electrocoagulation and electro-Fenton (EF-EC) to clean domestic wastewater. Domestic wastewater contains high amounts of organic, inorganic and microbial pollutants that cannot be usually treated in a single step. Here, to produce an effluent suitable for discharge in a single process step, a hybrid process combining electrocoagulation and electro-Fenton was simultaneously used to decrease chemical oxygen demand (COD), turbidity and total suspended solids (TSS) from domestic wastewater. The electrocoagulation–electro-Fenton process was firstly tested for the production of H₂O₂ using Ti–IrO₂ and vitreous carbon- or graphite electrodes arranged at the anode and the cathode, respectively. The concentration of H₂O₂ recorded at 1.5 A of current intensity during 60 min of electrolysis using vitreous carbon- and graphite electrodes at the cathode was 4.18 and 1.62 mg L^?1, respectively. By comparison, when the iron electrode was used at the anode, 2.05 and 1.06 mg L^?1 of H₂O₂ were recorded using vitreous carbon and graphite, respectively. The H₂O₂ concentration decrease was attributed to hydroxyl radical formation generated by the Fenton reaction. Electro-Fenton using iron electrode at the anode and vitreous carbon at the cathode with a current density imposed of 0.34 A dm^?2 ensures the removal efficiency of 50.1 % COD_T, 70.8 % TSS and 90.4 % turbidity. The electrocoagulation–electro-Fenton technique is therefore a promising secondary treatment to simultaneously remove organic, inorganic and microbial pollutants from domestic, municipal and industrial wastewaters.     

Removal of the herbicide amitrole from water by anodic oxidation and electro-Fenton

Here we demonstrate that an aqueous solution of the herbicide amitrole can be completely depolluted at pH 3.0 by anodic oxidation and electro-Fenton process. Anodic oxidation gives faster degradation with a boron-doped diamond anode than with a Pt anode. Electro-Fenton with a Pt anode and 1 mmol l ^–1 Fe²⁺ as catalyst yields the quickest depollution. Amitrole decay always follows a pseudo first-order reaction. NO₃^– and NH₄⁺ are accumulated in the medium during mineralization, although volatile N-products are also formed. These environmentally friendly electrochemical treatments could be applied to the remediation of wastewaters containing amitrole.     

The influence of some biological antioxid ants on the light emission from the oxytetracycline oxidation reaction

The effect of the Superoxide radical (O₂ ^–)‐, hydroxyl radical (HO')‐inhibitors, singlet oxygen (¹O₂)‐quenchers and catalase on the light emission during autoxidation reaction of oxytetracycline was measured. The influence of the ¹O₂‐quenchers was investigated quantitatively and the rate constants were established.     

Removal of carbamazepine from urban wastewater by sulfate radical oxidation

The occurrence of bioactive trace pollutants such as pharmaceuticals in natural waters is an emerging issue. Numerous pharmaceuticals are not completely removed in conventional wastewater treatment plants. Advanced oxidation processes may represent an interesting alternative to completely mineralize organic trace pollutants. In this article, we show that sulfate radicals generated from peroxymonosulfate/Co^II are more efficient than hydroxyl radicals generated from the Fenton’s reagent (H₂O₂/Fe^II) for the degradation of the pharmaceutical compound, carbamazepine. The second-order rate constant for the reaction of SO₄ ^·− with carbamazepine is 1.92·10⁹ M⁻¹ s⁻¹. In laboratory grade water and in real urban wastewater, SO₄ ^·− yielded a faster degradation of carbamazepine compared to HO^· . Under strongly oxidizing conditions, a nearly complete mineralization of carbamazepine was achieved, while under mildly oxidizing conditions, several intermediates were identified by LC–MS. These results show for the first time in real urban wastewater that sulfate radicals are more selective than hydroxyl radicals for the oxidation of an organic pollutant and may represent an interesting alternative in advanced oxidation processes.     

Study on degradation process of famotidine hydrochloride in aqueous samples

The kinetics of famotidine (FAM) transformation under the influence of various factors, important from the environmental point of view, was investigated in aqueous solutions. The degradation processes using UV, H₂O₂, UV/H₂O₂, H₂O₂/Fe²⁺, and UV/H₂O₂/Fe²⁺ were studied. Direct photolysis and H₂O₂-assisted photolysis showed a pseudo-first-order kinetics, while the Fenton and the photo-Fenton processes fit second-order kinetics. The provided experiments proved a high resistance of FAM to direct photolysis. Its stability depends highly on the pH of the reaction solutions. The rate of FAM direct photolysis in acidic solutions was almost negligible. The reaction rate of FAM photolysis at pH 8–9 was 3.7 × 10^?3 min^?1 with DT₅₀ about 3 h 7 min. It was found that the presence of H₂O₂ in the reaction environment enhances the rate of photolysis of FAM. The observed rates of reaction were 5.1 × 10^?3 min^?1 and 3.7 × 10^?3 min^?1 in acidic and basic solutions, respectively. The used Fenton systems appeared to be the most efficient in FAM removal. The rate of reaction depends on concentration of Fe²⁺ and H₂O₂. It was observed that the presence of UV-light enhances the reaction rate by two to six times in comparison to the classical Fenton system. Additionally, FAM behavior in natural water under solar irradiation was examined. The irradiation experiments were carried out in batch experiments with simulated sunlight.     

五氧化二钒类Fenton降解邻苯二甲酸二乙酯的机制研究

发展了基于五氧化二钒(V_2O_5)和过氧化氢(H_2O_2)的新型类Fenton体系,探索了此体系产生羟基(·OH)的机制及降解邻苯二甲酸二乙酯(DEP)的效率;并考察了V_2O_5投加量、H_2O_2浓度,以及草酸对DEP降解的影响。结果表明,当V_2O_5投加量为0.1 g·L-1,H_2O_2浓度为2.0 mmol·L-1,反应24 h后,对DEP(25 mg·L-1)的降解率可达61.1%,增加或降低V_2O_5投加量和H_2O_2浓度均不利于DEP的降解。利用电子顺磁共振技术(Electron Paramagnetic Resonance,EPR)耦合5,5-二甲基-1-吡咯啉氮氧化物(DMPO)为捕获剂对反应体系中的主导自由基进行鉴定,发现·OH是体系降解DEP的主要活性物种,利用苯甲酸作为探针分子实现了·OH的间接定量,并初步推测了V_2O_5活化H_2O_2的过程。     

Synthesis and antibacterial activity of a Fe3O4–AgCl nanocomposite against Escherichia coli

In this investigation, Fe₃O₄ magnetic nanoparticles (MNPs) were prepared by the alkalinization of an aqueous medium containing ferrous sulfate and ferric chloride. In the next step, a Fe₃O₄–AgCl magnetic nanocomposite was fabricated by the drop-by-drop addition of silver nitrate solution into a NaCl solution containing Fe₃O₄ MNPs. All prepared nanoparticles were characterized by transition electron microscopy (TEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). Both particle types varied in size from 2.5 to 20?nm, with an average size of 7.5?nm for Fe₃O₄ MNPs and 12.5?nm for Fe₃O₄–AgCl nanocomposites. The antibacterial effect of the Fe₃O₄ MNPs and fabricated Fe₃O₄–AgCl nanocomposites against Escherichia coli (ATCC 35218) were investigated by conventional serial agar dilution method using the Müller–Hinton Agar medium. The minimum inhibitory concentration was 4?mg?mL^?1 for Fe₃O₄ MNPs and 2?mg?mL^?1 for the Fe₃O₄–AgCl magnetic nanocomposites. Time-kill course assays showed that the Fe₃O₄–AgCl magnetic nanocomposites successfully killed all inoculated bacterial cells during an exposure time of 60?min. The antibacterial activity of recycled Fe₃O₄–AgCl magnetic nanocomposites over four 60?min cycles of antibacterial treatment was further tested against E. coli by the colony-forming unit (CFU) method. The antibacterial efficiency of the nanocomposites was constant over two cycles of antibacterial testing.     

Removal of chelated copper from wastewaters by Fe<Superscript>2+</Superscript>-based replacement–precipitation

We studied the removal mechanism and affecting factors of Fe²⁺-based replacement–precipitation process for treating CuEDTA-containing wastewaters. Since Fe²⁺ was easily oxidized to Fe³⁺ in the presence of oxygen, the chelated copper was removed by the synergetic effect of Fe³⁺ replacement and NaOH precipitation. Our experiments showed that the copper removal efficiency was considerably dependant on pH conditions of the solution and molar ratio of Fe²⁺/Cu²⁺.     

Novel coprecipitation–oxidation method for recovering iron from steel waste pickling liquor

Waste pickling liquors (WPLs) containing high concentrations of iron and acid are hazardous waste products from the steel pickling processes. A novel combined coprecipitation–oxidation method for iron recovery by Fe₃O₄ nanoparticle production from the WPLs was developed in this study. An oxidation–reduction potential monitoring method was developed for real-time control of the Fe²⁺/Fe³⁺ molar ratio. The key coprecipitation–oxidation parameters were determined using the orthogonal experimental design method. The use of promoters greatly improved the Fe₃O₄ nanoparticle crystallinity, size, magnetization, and dispersion. X-ray diffraction patterns showed that the produced Fe₃O₄ nanoparticles were single phase. The Fe₃O₄ nanoparticles were approximately spherical and slightly agglomerated. Vibrating sample magnetometry showed that the Fe₃O₄ nanoparticles produced from the WPLs had good magnetic properties, with a saturation magnetization of 80.206 emu·g^–1 and a remanence of 10.500 emu·g^–1. The results show that this novel coprecipitation–oxidation method has great potential for recycling iron in WPLs.

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Enhanced degradation of the antibiotic tetracycline by heterogeneous electro-Fenton with pyrite catalysis

There is actually increasing concern about the accumulation of antibiotics, such as tetracycline, in soil and water bodies. There is therefore a need for efficient methods to degrade antibiotics and thus clean waters. Here we tested the degradation of tetracycline using the heterogeneous electro-Fenton-pyrite method and compared the results with the conventional electro-Fenton method. The reaction was performed with a boron-doped diamond or Pt anode and carbon-felt cathode allowing electrogeneration of H₂O₂ from O₂ reduction. Results show an increasing tetracycline mineralization using the following methods: anodic oxidation with electrogenerated H₂O₂, electro-Fenton and then electro-Fenton-pyrite using boron-doped diamond. Ion-exclusion HPLC revealed the complete removal of malic malonic, succinic, acetic, oxalic and oxamic acids. Nitrogen present in tetracycline was mainly mineralized in NH₄ ⁺. The higher efficiency of electro-Fenton-pyrite is explained by self-regulation of soluble Fe²⁺ and pH to 3.0 from pyrite catalyst favoring larger ^·OH generation from Fenton’s reaction.     

Hydroxyl radical generation by redox cycling of some chemotherapeutic antibiotics

The anticancer drugs: adriamycin, farmorubicin and mitomycin C greatly enhance the generation of hydroxyl radicals (HO^.) from H₂O₂ in the presence of Co(II) ions (CoCl2) at pH 7.4 and 8, as measured by the deoxyribose assay. Catalase, hydroxyl radical scavengers (mannitol, cysteine, glutathione, thiourea, lactic dehydrogenase) inhibited the degradation of deoxyribose confirming that HO‐radicals are responsible for the degradation of the carbohydrate.     

Nano-titanium dioxide (TiO2)-induced changes affecting Cu2+-mediated alterations in bacterium Bacillus subtilis and α-amylase

Titanium dioxide (TiO₂) nanoparticles possess the potential to coexist with Copper (Cu²⁺) in soil. The individual and combined toxicity of these two chemicals was evaluated using the bacterium Bacillus subtilis, a known soil model bacterium. Cu²⁺ (6.25–50?µg?mL^?1) alone produced toxicity to bacteria as evidenced by the decreased cell viability and deceased α-amylase production. The addition of TiO₂ (50?mg?mL^?1) enhanced the Cu²⁺-induced decrease in cell viability but elevated amylase activity. TiO₂ did not markedly affect the growth rate and lag period. A primary cause of TiO₂ increasing Cu²⁺ toxicity is presumed to be associated with hydroxyl radical formation, while increased amylase activity is considered to arise from Cu²⁺ facilitating TiO₂ degradation ability.     

Fenton process for degradation of selected chlorinated aliphatic hydrocarbons exemplified by trichloroethylene, 1,1-dichloroethylene and chloroform

The degradation of selected chlorinated aliphatic hydrocarbons (CAHs) exemplified by trichloroethylene (TCE), 1,1-dichloroethylene (DCE), and chloroform (CF) was investigated with Fenton oxidation process. The results indicate that the degradation rate was primarily affected by the chemical structures of organic contaminants. Hydroxyl radicals (·OH) preferred to attack the organic contaminants with an electron-rich structure such as chlorinated alkenes (i.e., TCE and DCE). The dosing mode of Fenton’s reagent, particularly of Fe²⁺, significantly affected the degradation efficiency of studied organic compound. A new “time-squared” kinetic model, C = C _o exp(?k _obs t ²), was developed to express the degradation kinetics of selected CAHs. This model was applicable to TCE and DCE, but inapplicable to CF due to their varied reaction rate constants towards ?OH. Chloride release was monitored to examine the degree of dechlorination during the oxidation of selected CAHs. TCE was more easily dechlorinated thanDCE and CF.Dichloroacetic acid (DCAA) was identified as the major reaction intermediate in the oxidation of TCE, which could be completely removed as the reaction proceeded. No reaction intermediates or byproducts were identified in the oxidation of DCE and CF. Based on the identified intermediate, the reaction mechanism of TCE with Fenton’s reagent was proposed.     

Removal of acid yellow 36 using Box–Behnken designed photoelectro-Fenton: a study on removal mechanisms

Photoelectro-Fenton was applied for the removal of acid yellow 36 (AY36) from synthetic aqueous solution using iron electrodes. A Box–Behnken design was used for optimization of the effects of pH, H₂O₂ concentration, current density, and reaction time. Individual effects of these variables were more important than their interaction effects. The derived model was in good agreement with the experimental results. Total organic carbon was determined in solution and sludge in order to clarify the removal mechanism. Increase of H₂O₂ concentration and current density led to domination of oxidation and coagulation mechanisms, respectively. The effects of scavenging and inhibiting agents were also investigated: (1) presence of alcohols can reduce the efficiency through competition with dye for reaction with hydroxyl radicals; (2) anions (NO₃^?, HCO₃^?, and H₂PO₄^?) scavenged hydroxyl radicals and reduced decolorization of AY36.     

Catalytic ozonation performance and surface property of supported Fe3O4 catalysts dispersions

Fe₃O₄ was supported on mesoporous Al₂O₃ or SiO₂ (50 wt.%) using an incipient wetness impregnation method, and Fe₃O₄/Al₂O₃ exhibited higher catalytic efficiency for the degradation of 2,4-dichlorophenoxyacetic acid and para-chlorobenzoic acid aqueous solution with ozone. The effect and morphology of supported Fe₃O₄ on catalytic ozonation performance were investigated based on the characterization results of X-ray diffraction, X-ray photoelectron spectroscopy, BET analysis and Fourier transform infrared spectroscopy. The results indicated that the physical and chemical properties of the catalyst supports especially their Lewis acid sites had a significant influence on the catalytic activity. In comparison with SiO₂, more Lewis acid sites existed on the surface of Al₂O₃, resulting in higher catalytic ozonation activity. During the reaction process, no significant Fe ions release was observed. Moreover, Fe₃O₄/Al₂O₃ exhibited stable structure and activity after successive cyclic experiments. The results indicated that the catalyst is a promising ozonation catalyst with magnetic separation in drinking water treatment.     

Kinetics of hexavalent chromium reduction by iron metal

The kinetics of Cr(VI) reduction to Cr(III) by metallic iron (Fe⁰) was studied in batch reactors for a range of reactant concentrations, pH and temperatures. Nearly 86.8% removal efficiency for Cr(VI) was achieved when Fe⁰ concentration was 6 g/L (using commercial iron powder (< 200 mesh) in 120 min). The reduction of hexavalent chromium took place on the surface of the iron particles following pseudo-first order kinetics. The rate of Cr(VI) reduction increased with increasing Fe⁰ addition and temperature but inversely with initial pH. The pseudo-first-order rate coefficients (k _obs) were determined as 0.0024, 0.010, 0.0268 and 0.062 8 min^?1 when iron powder dosages were 2, 6, 10 and 14 g/L at 25°C and pH 5.5, respectively. According to the Arrehenius equation, the apparent activation energy of 26.5 kJ/mol and pre-exponential factor of 3 330 min^?1 were obtained at the temperature range of 288–308 K. Different Fe⁰ types were compared in this study. The reactivity was in the order starch-stabilized Fe⁰ nanoparticles > Fe⁰ nanoparticles > Fe⁰ powder > Fe⁰ filings. Electrochemical analysis of the reaction process showed that Cr(III) and Fe(III) hydroxides should be the dominant final products.