Electro-generation of hydrogen peroxide using a graphite cathode from exhausted batteries: study of influential parameters on electro-Fenton process

Analysis of factors influencing on Electro-Fenton and research on combination technology (II): a review

The principle of Fenton reagent is to produce ·OH by mixing H2O2 and Fe2+ to realize the oxidation of organic pollutants, although Fenton reagent has the advantages of non-toxicity and short reaction time, but there are its related defects. The Fenton-like technology has been widely studied because of its various forms and better results than the traditional Fenton technology in terms of pollutant degradation efficiency. This paper reviews the electro-Fenton technology among the Fenton-like technologies and provides an overview of the homogeneous electro-Fenton. It also focuses on summarizing the effects of factors such as H2O2, reactant concentration, reactor volume and electrode quality, reaction time and voltage (potential) on the efficiency of electro-Fenton process. It is shown that appropriate enhancement of H2O2 concentration, voltage (potential) and reaction volume can help to improve the process efficiency; the process efficiency also can be improved by increasing the reaction time and electrode quality. Feeding modes of H2O2 have different effects on process efficiency. Finally, a considerable number of experimental studies have shown that the combination of electro-Fenton with ultrasound, anodic oxidation and electrocoagulation technologies is superior to the single electro-Fenton process in terms of pollutant degradation.

Hydrogen peroxide electrogeneration from O2 electroreduction: A review focusing on carbon electrocatalysts and environmental applications

Hydrogen peroxide (H2O2) stands as one of the foremost utilized oxidizing agents in modern times. The established method for its production involves the intricate and costly anthraquinone process. However, a promising alternative pathway is the electrochemical hydrogen peroxide production, accomplished through the oxygen reduction reaction via a 2-electron pathway. This method not only simplifies the production process but also upholds environmental sustainability, especially when compared to the conventional anthraquinone method. In this review paper, recent works from the literature focusing on the 2-electron oxygen reduction reaction promoted by carbon electrocatalysts are summarized. The practical applications of these materials in the treatment of effluents contaminated with different pollutants (drugs, dyes, pesticides, and herbicides) are presented. Water treatment aiming to address these issues can be achieved through advanced oxidation electrochemical processes such as electro-Fenton, solar-electro-Fenton, and photo-electro-Fenton. These processes are discussed in detail in this work and the possible radicals that degrade the pollutants in each case are highlighted. The review broadens its scope to encompass contemporary computational simulations focused on the 2-electron oxygen reduction reaction, employing different models to describe carbon-based electrocatalysts. Finally, perspectives and future challenges in the area of carbon-based electrocatalysts for H2O2 electrogeneration are discussed. This review paper presents a forward-oriented viewpoint of present innovations and pragmatic implementations, delineating forthcoming challenges and prospects of this ever-evolving field.

Biodegradation and Decolorization of Crystal Violet Dye by Cocultivation with Fungi and Bacteria

Microbial degradation of dyes is vital to understanding the fate of dyes in the environment. In this study, a fungal strain A-3 and a bacterial strain L-6, which were identified as Aspergillus fumigatus and Pseudomonas fluorescens, respectively, had been proven to efficiently degrade crystal violet (CV) dye. The decolorization of CV dye by fungal and bacterial cocultivation was investigated. The results showed that the decolorization rate of cocultures was better than monoculture (P. fluorescens in L-6 (PF), and that of A. fumigatus A-3 (AF)). Furthermore, enzymatic analysis further revealed that Lac, MnP, Lip, and NADH-DCIP reductases were involved in the biodegradation of CV dyes. UV-visible spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and gas chromatography-mass spectrometry (GC-MS) were used to examine the degradation products. GC-MS analysis showed the presence of 4-(dimethylamino) benzophenone, 3-dimethylaminophenol, benzyl alcohol, and benzaldehyde, indicating that CV was degraded into simpler compounds. The phytotoxicity tests revealed that CV degradation products were less toxic than the parent compounds, indicating that the cocultures detoxified CV dyes. As a result, the cocultures are likely to have a wide range of applications in the bioremediation of CV dyes.

Electrogeneration of H2O2 through carbon-based ink on Al foam for electro-Fenton treatment of micropollutants in water

In the present work, the catalytic efficiency of inks based on different carbon materials, namely activated carbon (AC), carbon graphite (CG), and carbon black (CB) was investigated for the oxygen reduction reaction (ORR). Additionally, we explored the feasibility of using this ink as a coating for an Aluminum foam (Alfoam) cathode in an electrochemical cell. The goal was to utilize this setup to produce hydrogen peroxide (H2O2) in the electro-Fenton (EF) process, targeting for treating water contaminated with contaminants of emerging concern (CECs). Among the materials investigated, all of them exhibited the ability to facilitate the ORR. However, AC proved to be the most suitable material due to its optimal balance between physical and electrocatalytic properties, thus enabling the formation of H2O2. When the different inks were applied to the surface of aluminum foam, it was observed that only the ink based on carbon black CB achieved a homogeneous distribution with the same ink quantity. As a result, it was observed that the Alfoam/CB electrode exhibited the highest H2O2 generation capacity, producing 45.6 mg L-1, followed by electro-generation of 5.1 mg L-1 using Alfoam/AC and 11 mg L-1 using Alfoam/CG. Furthermore, the application of Alfoam/CB in EF processes allowed for the almost complete degradation of 15 emerging contaminants of concern (CECs) present in secondary effluent. The innovative outcome of this study positions the developed technology as a promising and effective alternative for the treatment of water contaminated with CECs, demonstrating significant potential for industrial-scale application.

Glucose driven self-sustained electro-Fenton platform for remediation of 2,4-dichlorophenoxy herbicide contaminated water

As electrochemical oxidation technologies are energy-intensive, they are sparsely included in wastewater treatment plants. This study demonstrates a self-reliable glucose driven-electro-Fenton (GD-EF) system for decontamination of 2,4-dichlorophenoxy (2,4-D) herbicides without the supply of external current or voltage. It incorporates a cathode (graphite) which accepts electrons from abiotic glucose oxidation at anode (Pt/Ti or BDD or PbO2/Cu/Ti) and generates in situ H2O2. For the first time, the ability of Pt/Ti, BDD, and PbO2/Cu/Ti anodes in GD-EF and their influence on 2,4-D decontamination rate have been studied. Pt/Ti and PbO2/Cu/Ti exhibited maximum power densities of 60.42 and 219.3 µW cm-2, respectively than BDD (2.418 µW cm-2). Even though Pt/Ti fuel cell exhibited lower power density than the PbO2/Cu/Ti - fuel cell, it had a faster 2,4-D degradation rate of k = 18 × 10-3 s-1. The generated cathodic potential of -0.275 mV vs. Ag/AgCl in the Pt/Ti-fuel cell was sufficient to produce 23 mg L-1h-1 of H2O2. The high performance liquid chromatography analysis reveals the complete transformation of 2,4-D in 540 min and its degradation by 95% in 1080 min. This finding paves the way for greener decontamination of bio-recalcitrant herbicides with zero electrochemical energy consumption.

An efficient system for electro-Fenton oxidation of pesticide by a reduced graphene oxide-aminopyrazine@3DNi foam gas diffusion electrode

A stable rGO-AmPyraz@3DNiF gas diffusion electrode was prepared via modification of 3D nickel foam (3D-NiF) with aminopyrazine functionalized reduced graphene oxide (rGO-AmPyraz) for the electro Fenton (EF) process. The generation capacity of H₂O₂ and OH radicals by this electrode was assessed relative to 3DNiF and rGO-AmPyraz@indium tin oxide (ITO) electrodes and with/without a coated Fe₃O₄ plate. The rGO-AmPyraz@3DNiF electrode showed the maximum production of these radicals at 2.2 mmol h^-1 and 410 μmol h^-1, respectively (pH 3) with the least leaching of Ni²⁺ such as < 0.5 mg L^-1 even after 5 cycles (e.g., relative to 3DNiF (24 mg L^-1). Such control on Ni ion leaching was effective all across the tested pH from 3 to 8.5. Its H₂O₂ generation capacity was far higher than that of the nanocarbon supported on commercially available ITO conductive glass. The mineralization of dichlorvos (at initial concentration: 50 mg L^-1) was confirmed with its complete degradation as the concentrations of the end products (e.g., free Cl^-1 (5.36 mg L^-1) and phosphate (12.89 mg L^-1)) were in good agreement with their stoichiometric concentration in dichlorvos. As such, the proposed system can be recommended as an effective electrode to replace nanocarbon-based product commonly employed for EF processes.