Fenton-like processes have been studied widely in recent years and are considered promising for organic wastewater treatment. Due to the demand for high efficiency wastewater treatment, a summary of the study status of Fenton-like processes is necessary to develop a novel and high efficiency organic wastewater treatment method. In this review, some important effect parameters (pH, H2O2 dosage, catalyst dosage, temperature) in hetero-/homo-geneous Fenton-like processes are discussed, and then the physical field/phenomenon-assisted hetero-/homo-geneous Fenton-like processes are presented. After that, catalyst types and the evaluation of wastewater treatment costs for various Fenton-like processes are summarized and discussed. Finally, possible future research directions and some guidelines for Fenton-like processes are given.

A review on Fenton-like processes for organic wastewater treatment

A critical review of the application of chelating agents to enable Fenton and Fenton-like reactions at high pH values.

Dyes are used in various industries as coloring agents. The discharge of dyes, specifically synthetic dyes, in wastewater represents a serious environmental problem and causes public health concerns. The implementation of regulations for wastewater discharge has forced research towards either the development of new processes or the improvement of available techniques to attain efficient degradation of dyes. Catalytic oxidation is one of the advanced oxidation processes (AOPs), based on the active radicals produced during the reaction in the presence of a catalyst. This paper reviews the problems of dyes and hydroxyl radical-based oxidation processes, including Fenton's process, non-iron metal catalysts, and the application of thin metal catalyst-coated tubular reactors in detail. In addition, the sulfate radical-based catalytic oxidation technique has also been described. This study also includes the effects of various operating parameters such as pH, temperature, the concentration of the oxidant, the initial concentration of dyes, and reaction time on the catalytic decomposition of dyes. Moreover, this paper analyzes the recent studies on catalytic oxidation processes. From the present study, it can be concluded that catalytic oxidation processes are very active and environmentally friendly methods for dye removal.

Catalytic Oxidation Process for the Degradation of Synthetic Dyes: An Overview.

Degradation of benzotriazole (BZA) as an emerging contaminant by a novel Fenton-like reaction was investigated using a catalyst prepared by incorporating Cu into mesoporous MnO2 (mesoporous Cu/MnO2, MCM). Catalysts were synthesized with different Cu contents, and were characterized by N2 adsorption–desorption, X-ray photoelectron spectroscopy, ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, and temperature-programmed reduction (TPR)-H2. The MCM functioned via surface chemisorption and redox reaction that was confirmed by intermediates identification, XPS and TPR analysis, followed by a Fenton-like oxidation derived by surface Cu+ and Mn3+, to provide high degradation efficiency for BZA in solution. Fourier transform infrared (FT-IR) spectroscopy result also verified the surface adsorption and Fenton-like reaction. MCM exhibited much higher adsorption and catalytic activity in the Fenton reaction than pure MnO2 or CuO. The effect of Cu content in MCM, catalyst dose, H2O2 dose, and solution pH were investigated. BZA degradation was high in deionized water (removal efficiency = 89%) and moderate in wastewater treatment plant effluent (removal efficiency = 56%) after 60-min reaction at an initial pH of 7.13, which could be developed by adjusting the dose of catalyst or H2O2. A possible mechanism for the reaction is proposed. This involves surface adsorption with copper and a redox reaction with Mn3+, followed by a copper–manganese cycle-derived Fenton-like reaction.

Degradation of benzotriazole by a novel Fenton-like reaction with mesoporous Cu/MnO2: Combination of adsorption and catalysis oxidation

Generation of hydroxyl radicals in the Fenton system (FeII /H2 O2 ) is seriously limited by the sluggish kinetics of FeIII reduction and fast FeIII precipitation Here, boron crystals (C-Boron) remarkably accelerate the FeIII /FeII circulation in Fenton-like systems (C-Boron/FeIII /H2 O2 ) to produce a myriad of hydroxyl radicals with excellent efficiencies in oxidative degradation of various pollutants The surface B-B bonds and interfacial suboxide boron in the surface B12 icosahedra are the active sites to donate electrons to promote fast FeIII reduction to FeII and further enhance hydroxyl radical production via Fenton chemistry The C-Boron/FeIII /H2 O2 system outperforms the benchmark Fenton (FeII /H2 O2 ) and FeIII -based sulfate radical systems The reactivity and stability of crystalline boron is much higher than the popular molecular reducing agents, nanocarbons, and other metal/metal-free nanomaterials

Fast and Long‐Lasting Iron(III) Reduction by Boron Toward Green and Accelerated Fenton Chemistry

We examined the degradation of nitrobenzene (NB) by modified Fenton reaction at near neutral pH conditions using Fe II –glutamate complex as a source of Fe 2+ . The reaction was conducted using 0.04 mM (5 mg L −1 ) of NB in presence of 65 mM H 2 O 2 at room temperature. Complex concentrations of 5, 10, 15 and 20 mM (Fe 2+  = 0.81, 1.62, 2.43 and 3.23 mM) were assayed and showed effective rates of NB degradation with t 1/2 values of 17, 6.2, 4.8 and 1.85 min, respectively. In the pH range 5–7 the complex activity is pH-dependent, and the optimal pH was 6.3. The degradation was monitored by solid-phase microextraction in combination with GC analysis. The rate of degradation recorded at near neutral pH in presence of 20 mM of Fe-complex was equal to that obtained in presence of Fe 2+ (2.5 mM) at pH 2.7. Glutamate complexes formed with Cu 2+ or Co 2+ did not show the improved degradation observed in case of Fe–glutamate. Furthermore, the introduction of the chelating agent as a free ion into the reaction medium containing Fe 2+ did not improve the degradation of NB at neutral pH conditions.

O.I.H. Dimitry

Papers

Degradation of nitrobenzene at near neutral pH using Fe2+–glutamate complex as a homogeneous Fenton catalyst

Ultrasonic assisted-Fenton-like degradation of nitrobenzene at neutral pH using nanosized oxides of Fe and Cu.

Extending the working pH of nitrobenzene degradation using ultrasonic/heterogeneous Fenton to the alkaline range via amino acid modification

Investigation on the sonocatalytic degradation of nitrobenzene using heterogeneous nanostructured catalysts in absence and presence of surfactant