Degradation of trans-ferulic acid in acidic aqueous medium by anodic oxidation, electro-Fenton and photoelectro-Fenton

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.

Activated carbon fiber as an efficient co-catalyst toward accelerating Fe2+/Fe3+ cycling for improved removal of antibiotic cefaclor via electro-Fenton process using a gas diffusion electrode

The electro-Fenton (EF) based on gas-diffusion electrodes (GDEs) reveals promising application prospective towards recalcitrant organics degradation because such GDEs often yields superior H2O2 generation efficiency and selectivity. However, the low efficiency of Fe2+/Fe3+ cycle with GDEs is always considered to be the limiting step for the EF process. In this study, activated carbon fiber (ACF) was firstly employed as co-catalyst to facilitate the performance of antibiotic cefaclor (CEC) decomposition in EF process. It was found that the addition of ACF co-catalyst achieved a rapid Fe2+/Fe3+ cycling, which significantly enhanced Fenton's reaction and hydroxyl radicals (•OH) generation. X-ray photoelectron spectroscopy (XPS) results indicated that the functional groups on ACF surface are related to the conversion of Fe3+ into Fe2+. Moreover, DMSO probing experiment confirmed the enhanced •OH production in EF + ACF system compared to conventional EF system. When inactive BDD and Ti4O7/Ti anodes were paired to EF system, the addition of ACF could significantly improve mineralization degree. However, a large amount of toxic byproducts, including chlorate (ClO3-) and perchlorate (ClO4-), were generated in these EF processes, especially for BDD anode, due to their robust oxidation capacity. Higher mineralization efficiency and less toxic ClO4- generation were obtained in the EF + ACF process with Ti4O7/Ti anode. This presents a novel alternative for efficient chloride-containing organic removal during wastewater remediation.

Graphene-Based Electrochemical Sensing Platform for Rapid and Selective Ferulic Acid Quantification

Due to the multitude of physiological functions, ferulic acid (FA) has a wide range of applications in the food, cosmetic, and pharmaceutical industries. Thus, the development of rapid, sensitive, and selective detection tools for its assay is of great interest. This study reports a new electroanalytical approach for the quantification of ferulic acid in commercial pharmaceutical samples using a sulphur-doped graphene-based electrochemical sensing platform. The few-layer graphene material (exf-SGR) was prepared by the electrochemical oxidation of graphite, at a low applied bias (5 V), in an inorganic salt mixture of Na2S2O3/(NH4)2SO4 (0.3 M each). According to the morpho-structural characterization of the material, it appears to have a high heteroatom doping degree, as proved by the presence of sulphur lines in the XRD pattern, and the C/S ratio was determined by XPS investigations to be 11.57. The electrochemical performances of a glassy carbon electrode modified with the exf-SGR toward FA detection were tested by cyclic voltammetry in both standard laboratory solutions and real sample analysis. The developed modified electrode showed a low limit of detection (30.3 nM) and excellent stability and reproducibility, proving its potential applicability as a viable solution in FA qualitative and quantitative analysis.

Solar photoelectro-Fenton: A very effective and cost-efficient electrochemical advanced oxidation process for the removal of organic pollutants from synthetic and real wastewaters

Recalcitrant and toxic organic pollutants from wastewaters are scarcely removed in conventional wastewater treatment plants. To preserve the water quality, organics need to be removed by developing powerful oxidation technologies. Our laboratory proposed in 2007 a potent electrochemical advanced oxidation process (EAOP) for wastewater remediation, so-called solar photoelectro-Fenton (SPEF). This review summarizes the advances of this emerging technology up to 2022, making evident its effectiveness and cost-efficiency for the destruction of usual organic pollutants. The simultaneous action of generated hydroxyl radicals and the photolysis by sunlight explains the high oxidation power of SPEF respect to other EAOPs. The review is initiated by describing the fundamentals of the process to remark the role of the produced oxidants and the benefits of using solar irradiation in its performance. The photoelectrochemical systems used (bench tank reactor and solar pre-pilot flow plant) and the assessment of the operating variables are discussed. The characteristics of the most common homogeneous SPEF for the degradation and mineralization of several synthetic solutions of industrial chemicals, herbicides, pharmaceuticals, and synthetic organic dyes, as well as of some real wastewaters, are further described. The influence of the photoelectrochemical cell, electrodes, solution pH, electrolyte composition, Fe²⁺ and pollutant concentration, and current density is analyzed. The performance of a homogeneous SPEF-like process with active chlorine and heterogeneous SPEF processes with solid catalysts such as Fe₃O₄ and sodium vermiculite is also discussed. Finally, the advances of homogeneous SPEF combined with other techniques like solar photocatalysis, solar photoelectrocatalysis, anaerobic digestion, and nanofiltration are reported.

Flow-through heterogeneous electro-Fenton system using a bifunctional FeOCl/carbon cloth/activated carbon fiber cathode for efficient degradation of trimethoprim at neutral pH

The synthesis of multifunctional cathode with high-efficiency and stable catalytic activity for simultaneously producing and activating H₂O₂ is an effective way for promoting the performance of heterogeneous electro-Fenton process (HEF). In addition, accelerating mass transfer by adopting a flow-through reactor is also great importance because of its better utilization of catalysts and adequate contact of the contaminant with the oxidants generated on the electrode surface. Herein, a novel flow-through HEF (FHEF) system was designed for the degradation of trimethoprim (TMP) using bifunctional cathode with a sandwich structure FeOCl nanosheets loaded onto carbon cloth (CC) and activated carbon fiber (ACF) (FeOCl/CC/ACF). The cathode exhibited excellent performance in activating H₂O₂ for the in-situ generation of hydroxyl radicals (^•OH). The electron spin resonance (ESR) measurements and radical quenching tests proved that the high production of ^•OH in the FHEF process was favorable to the high catalytic efficiency. 25 mg L^-1 TMP was entirely degraded after 60 min, with the TOC removal of 62.6% (180 min) at pH 6.8, 9.0 mA cm^-2, and flux rate 210 mL min^-1. Moreover, the degradation rate still could reach 83% (60 min) after 10 cycles without obvious valence and crystal phase changes. Simultaneously, the current utilization rate has also been greatly enhanced, with an average current efficiency of 69.9% and a low energy consumption of 0.28 kWh kg^-1. The reasonable degradation pathways for TMP were proposed based on the UPLC-QTOF-MS/MS results. Finally, the results of toxicological simulation showed a declining trend in the toxicity of the samples during TMP degradation. These results claim that the FeOCl/CC/ACF-FHEF system is an efficient and economical technology for the treatment of organic contaminants in effluents.

Magnetic TiO2/Fe3O4-Chitosan Beads: A Highly Efficient and Reusable Catalyst for Photo-Electro-Fenton Process

Heterogeneous photo-electro-Fenton process is an attractive technology for the removal of recalcitrant pollutants. To better exploit the presence of an irradiation source, a bifunctional catalyst with TiO2 nanoparticles embedded into an iron–chitosan matrix was developed. The catalytic activity of the catalyst was improved by the optimization of the loaded TiO2content. The prepared composite catalysts based on TiO2, Fe3O4 and chitosan were called TiO2/Fe3O4-CS beads. The best catalyst with an optimal ratio TiO2/Fe = 2 exhibited a high efficiency inthe degradation and mineralization of chlordimeform (CDM) insecticide. Under the optimum conditions (concentration of catalyst equal to 1 g L−1 and applied current intensity equal to 70 mA), a real effluent doped with 30 mg L−1 of CDM was efficiently treated, leading to 80.8 ± 1.9% TOC reduction after 6 h of treatment, with total removal of CDM after only 1 h.The generated carboxylic acids and minerals wereidentified and quantified. Furthermore, the stability and reusability of the developed catalyst was examined, and an insignificant reduction in catalytic activity was noticed forfour consecutive cycles of the photo-electro-Fenton process. Analyses using SEM, XRD and VSM showed a good stability of the physicochemical properties of the catalyst after use.

Validated Stability-Indicating GC-MS Method for Characterization of Forced Degradation Products of Trans-Caffeic Acid and Trans-Ferulic Acid

When dealing with simple phenols such as caffeic acid (CA) and ferulic acid (FA), found in a variety of plants, it is very important to have control over the most important factors that accelerate their degradation reactions. This is the first report in which the stabilities of these two compounds have been systematically tested by exposure to various different factors. Forced degradation studies were performed on pure standards (trans-CA and trans-FA), dissolved in different solvents and exposed to different oxidative, photolytic and thermal stress conditions. Additionally, a rapid, sensitive, and selective stability-indicating gas chromatographic-mass spectrometric method was developed and validated for determination of trans-CA and trans-FA in the presence of their degradation products. Cis-CA and cis-FA were confirmed as the only degradation products in all the experiments performed. All the compounds were perfectly separated by gas chromatography (GC) and identified using mass spectrometry (MS), a method that additionally elucidated their structures. In general, more protic solvents, higher temperatures, UV radiation and longer storage times led to more significant degradation (isomerization) of both trans-isomers. The most progressive isomerization of both compounds (up to 43%) was observed when the polar solutions were exposed to daylight at room temperature for 1 month. The method was validated for linearity, precision as repeatability, limit of detection (LOD) and limit of quantitation (LOQ). The method was confirmed as linear over tested concentration ranges from 1−100 mg L⁻¹ (r²s were above 0.999). The LOD and LOQ for trans-FA were 0.15 mg L⁻¹ and 0.50 mg L⁻¹, respectively. The LOD and LOQ for trans-CA were 0.23 mg L⁻¹ and 0.77 mg L⁻¹, respectively.

Degradation of caffeic acid by dielectric barrier discharge plasma combined with Ce doped CoOOH catalyst

Herein, Ce doped CoOOH was used as the catalyst for caffeic acid (CA) degradation by dielectric barrier discharge (DBD) plasma. The treatment performance and catalytic mechanism were studied by a series of experiments and density functional theory (DFT) simulations. The results show that the doping amounts of Ce significantly influenced the catalytic performance of CoOOH in DBD plasma, and the catalytic effect reached maximum when the molar ratio of Ce to Co was 1:9. CA was 100 % degraded by Ce₁/Co₉OOH/DBD with 10 min treatment, while only 75.6 % of CA was degraded by 10 min DBD treatment. Transformation of O₃ and H₂O₂ to ⋅OH was mainly responsible for the catalytic effect. The content of oxygen vacancies and unsaturated Co (Lewis acid sites) of CoOOH was increased by doping Ce according to the results of experiments and simulations, and the change was conducive to the catalytic reactions. DFT simulations also indicated that DBD generated O₃ and H₂O₂ were decomposed to O atoms, OH groups and free OH by Ce/CoOOH. The presence of reductive species in DBD plasma was confirmed, and ⋅H was a kind of important reactive specie for CA degradation. CA degradation pathway was proposed based on the detected degradation products.

Oxidation of pollutants via an electro-Fenton-like process in aqueous media using iron–zeolite modified electrodes

Eco-friendly modified electrodes based on zeolites are applied for electro-Fenton dye oxidation without the addition of H₂O₂ at room temperature.

Simultaneous persulfate activation by electrogenerated H2O2 and anodic oxidation at a boron-doped diamond anode for the treatment of dye solutions

The development of new or upgraded electrochemical water treatment technologies is considered a topic of great interest. Here, Tartrazine azo dye solutions were treated by means of a quite innovative dual electrochemical persulfate (S₂O₈^2-, PS) activation that combines H₂O₂ generation at an air-diffusion cathode and anodic oxidation (AO) at a boron-doped diamond (BDD) anode using a stirred tank reactor. This so-called AO-H₂O₂/PS process was compared to AO with stainless steel cathode, both in 50 mM Na₂SO₄ medium, finding the oxidation power increasing as: AO < AO-H₂O₂ < AO/PS < AO-H₂O₂/PS. In the latter, the dye and its products were mainly destroyed by: (i) hydroxyl radicals, formed either from water oxidation at BDD surface or via reaction between H₂O₂ and S₂O₈^2-, and (ii) sulfate radical anion, formed from the latter reaction, thermal PS activation and cathodic S₂O₈^2- reduction. Hydroxyl radicals prevailed as oxidizing agents, as deduced from trials with tert-butanol and methanol. The reaction between S₂O₈^2- and accumulated H₂O₂ was favored as temperature increased from 25 to 45 °C. The effect of PS content up to 36 mM, dye concentration within the range 0.22-0.88 mM, current density (j) between 8.3 and 33.3 mA cm^-2 and pH between 3.0 and 9.0 on the process performance was examined. All decolorization profiles agreed with a pseudo-first-order kinetics. The best results for treating 0.44 mM dye were attained with 36 mM PS at pH 3.0, j = 16.7 mA cm^-2 and 45 °C, yielding total loss of color, 62% TOC removal and 50% mineralization current efficiency after 360 min. The slow mineralization was attributed to the persistence of recalcitrant byproducts like maleic, acetic, oxalic, formic and oxamic acids. It is concluded that the novel AO-H₂O₂/PS process is more effective than AO/PS to treat Tartrazine solutions, being advisable to extend the study to other organic pollutants.

Conventional and emerging technologies for removal of antibiotics from wastewater

Antibiotics and pharmaceuticals related products are used to enhance public health and quality of life. The wastewater that is produced from pharmaceutical industries still contains noticeable amount of antibiotics, and this has remained one of the major environmental problems facing public health. The conventional wastewater remediation approach employed by the pharmaceutical industries for the antibiotics wastewater removal is unable to remove the antibiotics completely. Besides, municipal and livestock wastewater also contain unmetabolized antibiotics released by human and animal, respectively. The antibiotic found in wastewater leads to antibiotic resistance challenges, also emergence of superbugs. Currently, numerous technological approaches have been developed to remove antibiotics from the wastewater. Therefore, it was imperative to critically review the weakness and strength of these current advanced technological approaches in use. Besides, the conventional methods for removal of antibiotics such as Klavaroti et al., Homem and Santos also discussed. Although, membrane treatment is discovered as the ultimate choice of approach, to completely remove the antibiotics, while the filtered antibiotics are still retained on the membrane. This study found, hybrid processes to be the best solution antibiotics removal from wastewater. Nevertheless, real-time monitoring system is also recommended to ascertain that, wastewater is cleared of antibiotics.

Dielectric barrier discharge plasma with photocatalysts as a hybrid emerging technology for degradation of synthetic organic compounds in aqueous environments: A critical review

Dielectric barrier discharge (DBD) plasma has been recently used for removal of synthetic organic compounds (SOCs) from aqueous environments. The removal of SOCs by alone DBD is significantly limited by its high electricity needs and inefficient mineralization, which affects the further application of DBD for SOCs. The combined application of DBD with other technologies and the addition of a supplementary substance for energy-saving were proposed to resolve these problems. The addition of catalysts is considered to be a promising and innovative approach to increase the energy yield of DBD, improve the environment friendly of DBD, develop the variety of goal SOCs, and improve the removal efficiency of DBD system. Despite the increasing use of the coupling form of DBD and catalysts, as catalytic dielectric barrier discharge (CDBD), but it still requires a comprehensive review to summarize the last studies and highlight the future perspectives in this area. Therefore, this work is the first literature review aimed to critically assess the latest developments of catalysts coupling with DBD employed in aqueous environments. Moreover, performance evaluation, energy yield, toxicity, eco-friendly, and future perspectives of the CDBD systems for SOCs removal were discussed and overviewed. The results showed that the coupling of catalysts with DBD presents synergistic effects and had excellent removal performance for aqueous SOCs. Overall, it can be concluded that the essential principles of environmental and economic sustainability have been addressed for the removal of persistent pollutants from aqueous environments in the CDBD systems.

A review on the photoelectro-Fenton process as efficient electrochemical advanced oxidation for wastewater remediation. Treatment with UV light, sunlight, and coupling with conventional and other photo-assisted advanced technologies

Wastewaters containing recalcitrant and toxic organic pollutants are scarcely decontaminated in conventional wastewater facilities. Then, there is an urgent challenge the development of powerful oxidation processes to ensure their organic removal in order to preserve the water quality in the environment. This review presents the recent development of an electrochemical advanced oxidation process (EAOP) like the photoelectro-Fenton (PEF) process, covering the period 2010-2019, as an effective treatment for wastewater remediation. The high oxidation ability of this photo-assisted Fenton-based EAOP is due to the combination of in situ generated hydroxyl radicals and the photolytic action of UV or sunlight irradiation over the treated wastewater. Firstly, the fundamentals and characteristics of the PEF process are described to understand the role of oxidizing agents. Further, the properties of the homogeneous PEF process with iron catalyst and UV irradiation and the benefit of sunlight in the homogeneous solar PEF one (SPEF) are discussed, supported with examples over their application to the degradation and mineralization of synthetic solutions of industrial chemicals, herbicides, dyes and pharmaceuticals, as well as real wastewaters. Novel heterogeneous PEF processes involving solid iron catalysts or iron-modified cathodes are subsequently detailed. Finally, the oxidation power of hybrid processes including photocatalysis/PEF, solar photocatalysis/SPEF, photoelectrocatalysis/PEF and solar photoelectrocatalysis/SPEF, followed by that of sequential processes like electrocoagulation/PEF and biological oxidation coupled to SPEF, are analyzed.

Expanding the application of photoelectro-Fenton treatment to urban wastewater using the Fe(III)-EDDS complex

This work reports the first investigation on the use of EDDS as chelating agent in photoelectro-Fenton (PEF) treatment of water at near-neutral pH. As a case study, the removal of the antidepressant fluoxetine was optimized, using an electrochemical cell composed of an IrO₂-based anode an air-diffusion cathode for in-situ H₂O₂ production. Electrolytic trials at constant current were made in ultrapure water with different electrolytes, as well as in urban wastewater (secondary effluent) at pH 7.2. PEF with Fe(III)-EDDS (1:1) complex as catalyst outperformed electro-Fenton and PEF processes with uncomplexed Fe(II) or Fe(III). This can be explained by: (i) the larger solubilization of iron ions during the trials, favoring the production of ^•OH from Fenton-like reactions between H₂O₂ and Fe(II)-EDDS or Fe(III)-EDDS, and (ii) the occurrence of Fe(II) regeneration from Fe(III)-EDDS photoreduction, which was more efficient than conventional photo-Fenton reaction with uncomplexed Fe(III). The greatest drug concentration decays were achieved at low pH, using only 0.10 mM Fe(III)-EDDS, although complete removal in wastewater was feasible only with 0.20 mM Fe(III)-EDDS due to the greater formation of ^•OH. The effect of the applied current and anode nature was rather insignificant. A progressive destruction of the catalytic complex was unveiled, whereupon the mineralization mainly progressed thanks to the action of ^•OH adsorbed on the anode surface. Despite the incomplete mineralization using BDD as the anode, a remarkable toxicity decrease was determined. Fluoxetine degradation yielded F^- and NO₃^- ions, along with several aromatic intermediates. These included two chloro-organics, as a result of the anodic oxidation of Cl^- to active chlorine. A detailed mechanism for the Fe(III)-EDDS-catalyzed PEF treatment of fluoxetine in urban wastewater is finally proposed.

Nitrogen moieties -dominated Co-N-doped nanoparticle-modified cathodes in heterogeneous-electro-Fenton-like system for catalytic decontamination of EDTA-Ni(II)

Ethylenediaminetetraacetic acid (EDTA) could form stable complexes with toxic metals such as nickel due to its strong chelation. In this study, with the same doping level of Co and N, MoO₂ and ZIF-67 were used as precursors to prepare MoO₂@Co/N and FeC@Co/N electrocatalysts for the modified graphite felt cathodes in heterogeneous-electro-Fenton-like reaction (HEFL) system. The X-ray diffraction and X-ray photoelectron spectroscopy results indicated that both of the catalysts are dominated with pyridinic N (2.42% and 2.82%) upon co-doping Co/N, and FeC@Co/N exhibited an obviously higher additional sp-hybridized nitrogen (sp-N) peak. The co-doping of Co/N induced the lattice modifications to produce more lattice defects, where pyridinic N and sp-N, related with the active sites (C-N, Co-Nx), were formed at near-ring defects along sheet edges through the nitrogen replacement of CC groups. FeC@Co/N demonstrated superior oxygen reduction reaction catalytic activity in terms of Cyclic Voltammetry and Rotating Ring-disk Electrode, and exhibited the remarkably higher current density (30 mA) and lower onset potential (-0.208 V) in Linear Sweep Voltammetry analysis. In the FeC@Co/N/CF modified HEFL system, despite the generated H₂O₂ concentrations (62.5 mg L^-1) is not very high, the reducing reaction of ≡Fe(III)/Co(III)-OH could get the electron directly from the cathode, which would greatly reduce the consumption of H₂O_2, high utilization efficiency of H₂O₂ (η: 87.63%) could greatly improve the EDTA-Ni removal (97.5%) and TOC (92.6%). This work demonstrates the feasibility of utilizing FeC@Co/N/CF as a cathode for breaking metal-complex in HEFL process.

Enhanced Bio-Electro-Fenton degradation of phenolic compounds based on a novel Fe-Mn/Graphite felt composite cathode

Phenolic compounds are problematic byproducts generated from lignocellulose pretreatment. In this study, the feasibility degradation of syringic acid (SA), vanillic acid (VA), and 4-hydroxybenzoic acid (HBA) by Bio-Electro-Fenton (BEF) system with a novel Fe-Mn/graphite felt (Fe-Mn/GF) composite cathode were investigated. The nano-scale Fe-Mn multivalent composite catalyst with core shell structure distributed more evenly on GF surface to form a catalyst layer with higher oxygen reduction reaction performance. Accordingly, the maximum power density generated with Fe-Mn/GF cathode was 48.1% and 238.9% higher than Fe/GF and GF respectively, which further enhanced the in situ generation of H₂O₂ due to the superiority of nano-scale core shell structure and synergistic effect of Fe and Mn species. The degradation efficiency of the three phenolic compounds in the BEF system could reached 100% after optimization of influencing parameters. Furthermore, a possible SA degradation pathway by BEF process in the present system was proposed based on the detected intermediates. These results demonstrated an efficient approach for the degradation of phenolic compounds derived from lignocellulose hydrolysates.

Pharmaceutical wastewater treatment using UV-enhanced electro-Fenton process: Comparative study

In this research, treatment of a pharmaceutical wastewater (PhW) obtained from a factory by electro-Fenton (EF) and photoelectro-Fenton (PEF) processes was investigated. The effects of several parameters involving pH, current density, H₂ O₂ /Fe²⁺ molar ratio, volume ratio of H₂ O₂ /PhW, UVA light, and time were studied. The experiments were designed by Design Expert software, and response surface methodology (RSM) was applied to determine the optimum conditions for the highest COD removal. According to the analysis of variance (ANOVA), time was the most significant parameter on the process response (COD removal) followed by current density. The optimal conditions for 86.85% of COD removal through the EF process were at pH of 2.96, current density of 42.90 mA/cm² , H₂ O₂ /Fe²⁺ molar ratio of 3.78, volume ratio of H₂ O₂ /PhW of 1.37 ml/L, and reaction time of 58.49 min, while the optimal conditions for 93.00% of COD removal through PEF process were at pH of 2.91, current density of 43.71 mA/cm² , H₂ O₂ /Fe²⁺ molar ratio of 4.29, volume ratio of H₂ O₂ /PhW of 1.67 ml/L, UVA light of 6 W, and reaction time of 54.24 min. It was concluded that UVA light can increase the COD removal through PEF process around 7% more than that of the EF process at optimum conditions. PRACTITIONER POINTS: Treatment of a pharmaceutical wastewater by EF and PEF processes was investigated. Effects of several parameters were entirely studied on both the processes. RSM was applied to determine optimum conditions for the highest COD removal for both the processes. UVA light increased COD removal through PEF process (around 7%) at the optimum conditions.

Mineralization of cefoperazone in acid medium by the microwave discharge electrodeless lamp irradiated photoelectro-Fenton using a RuO2/Ti or boron-doped diamond anode

The mineralization of 125 mL of 50-300 mg L^-1 cefoperazone (CFPZ) has been comparatively studied by electrochemical advanced oxidation processes (EAOPs) like anodic oxidation (AO), electro-Fenton (EF) and photoelectro-Fenton (PEF) with a RuO₂/Ti or boron-doped diamond (BDD) anode and an activated carbon fiber (ACF) cathode. A microwave discharge electrodeless lamp (MDEL) was used as the UV source in PEF process. CFPZ decays always followed pseudo-first-order kinetics and their constant rates increased in the order: AO < EF < MDEL-PEF, regardless of anode types. Higher mineralization was achieved in all methods using BDD instead of RuO₂/Ti, while the most potent BDD-MDEL-PEF gave 88% mineralization under its optimum conditions of 0.36 A, pH 3.0 and 1.0 mmol L^-1 Fe²⁺. The synergistic mechanisms were explored by quantifying the electrogenerated H₂O₂ and formed ^•OH, in which 2.27 and 2.58 mmol L^-1 H₂O₂ were accumulated in AO-H₂O₂ with RuO₂/Ti or BDD anode, respectively, while 92.0 and 263.5 μmol L^{-1 •}OH were generated in EF with RuO₂/Ti or BDD anode, respectively. The oxidation power of EAOPs with different anodes was also compared by measuring the evolutions of NO₃^- and NH₄⁺ as well as four generated carboxylic acids including oxalic, oxamic, formic and fumaric acids.

Treatment of canola-oil refinery effluent using electrochemical methods: A comparison between combined electrocoagulation + electrooxidation and electrochemical peroxidation methods

A comparative study of combined electrocoagulation (EC) + electrooxidation (EO) and electrochemical peroxidation (ECP) treatment processes were carried out to treat canola oil refinery (COR) wastewaters. The effect of applied current density and operation time in the removal of organic pollutants were investigated and discussed. Total chemical oxygen demand (TCOD), soluble chemical oxygen demand (sCOD), total organic carbon (TOC), dissolved organic carbon (DOC) and total suspended solids (TSS) were measured. Using only EC process was found to be significantly successful in removing suspended and colloidal pollutants and could remove more than 90% TCOD and 80% of TOC at current densities between 0.91 and 13.66 mA cm^-2. From the statistical model, the optimized conditions for TCOD at a current density of 7.61 mA cm^-2 and TOC at 7.99 mA cm^-2 under 40 min operation, validated to remove 93.45% and 94.5% respectively. However, the maximum removal of dissolved organic pollutants was relatively low in EC process and reported to be 75% for sCOD and 74% for DOC. Therefore, EC + EO process were run to increase the removal of sCOD and DOC to 99 and 95%, respectively. On the other hand, treatment using ECP process achieved a removal of sCOD and DOC between 77 and 86%. TSS were removed completely in both EC + EO and ECP processes. A statistical model was applied to compare the performance of two methods and found that the combined EC + EO process provided lightly better treatment compared to ECP method.

Synergistic degradation of trans-ferulic acid in aqueous solution by dielectric barrier discharge plasma combined with ozone

Trans-ferulic acid (FA), extensively used in pharmaceutical and olive oil industries, causes huge risks to ecological environment due to its biotoxicity and phytotoxicity, leading to the difficulty of biochemical processes in treating FA wastewater. In this study, synergistic degradation of FA via dielectric barrier discharge (DBD) plasma and O₃ (plasma-ozone) was studied. The results showed that FA degradation efficiency reached 96.9% after a 40-min treatment by plasma-ozone process, and the energy efficiency of FA degradation was increased by 62.5 and 24.5% compared to single DBD plasma and ozonation treatment. Moreover, FA degradation rate constant in plasma-ozone process was 41% higher compared with the sum of single DBD plasma and ozonation, indicating a significant synergistic effect. Radical diagnosis experiments reveal that a profound increase of ·OH yield through peroxone (H₂O₂/O₃) and UV/O₃ pathways is the important mechanism of synergistic degradation of FA in plasma-ozone process, while e_aq^- played little role in FA degradation. A degradation pathway of FA by plasma-ozone was also proposed according to the detected intermediates from EEM and LC-MS. This work revealed that plasma-ozone process is an alternative process for FA treatment, and the findings are helpful for understanding FA degradation characteristics and synergistic mechanisms in plasma-ozone process.

Towards sustainable removal of methylthioninium chloride by using adsorption-electroradical regeneration

The current need for effective regeneration processes to be used in valorization of spent adsorbent demands the research of novel alternative techniques such as application of Advances Oxidation Processes. In this sense, the recent application of electroradical (ER) processes turned out to be very promising in terms of the drugs degradation from different environments. Thus, in this study, harnessing of a low cost natural adsorbent, Tunisian bentonite (BE), was evaluated for the removal of a model drug such as methylthioninium chloride (MC), and then its regeneration by ER processes was demonstrated. Initially, the BE was characterized and the adsorption of the MC was studied. This process followed a pseudo-first order kinetic and Langmuir isotherm fitted well to data reaching uptake values around 145-155 mg g^-1. After that, BE regeneration by an ER process such as electro-Fenton process was ascertained. Due to the high buffering capacity of the BE, the addition of citric acid (1 mM) was necessary in order to assure the acidic medium to favor the oxidation reaction. By operating under optimized experimental conditions (current intensity 300 mA, pH 3, Fe²⁺ (1 mM) and citric acid (1 mM)) near complete adsorbent regeneration was achieved after 300 min of treatment and the pseudo-first-order model fitted well the degradation data. Furthermore, the adsorbent was efficiently used in successive cycles of adsorption-regeneration without operational problems that proved the efficiency of this technology. From the obtained results, a side-by-side configuration was designed and simulated, confirming the viability of the design at large scale.

Co-N-doped MoO2 modified carbon felt cathode for removal of EDTA-Ni in electro-Fenton process

Metal ions removal is inhibited in aqueous solution containing ethylenediaminetetraacetic acid (EDTA). In this study, the non-noble metals-based Co-N-doped MoO₂ nanowires (Co-N-MoO₂) were successfully synthesized using cyanamide and Co(Ac)₂ as precursors by pyrolysis, then immobilized on carbon felt (CF), and firstly used as cathode to remove EDTA-Ni complex through oxygen reduction reaction (ORR) in electro-Fenton (EF) process. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that a synergetic coupling effect of doping of N and Co induced structural modifications of MoO₂ lattice, and produced more lattice defects. The electrochemical analysis results showed that the superior ORR electrochemical catalysis activities were obtained at pH = 3 with the lowest cathodic peak potentials (- 0.157 V vs. Ag/AgCl), the highest electrochemical active surface area (EASA: 3.971 mC cm^-2), the extraordinarily high of the ring current (35.5 μA) and high H₂O₂ yield (> 20%). Under the optimum conditions, about 68% of EDTA-Ni was removed with the Co-N-MoO₂/CF as cathode after 120 min with lower specific energy consumption (0.0226 kW h mg^-1 (DOC)) in EF system. Mechanism analysis indicated that the production of strong oxidizing property of hydroxyl radical (•OH) on the cathode played an important role in the removal of EDTA-Ni in the EF process, synergetic effect of cobalt and nitrogen co-doped could facilitate the high generation of H₂O₂, which greatly promote the formation of •OH. The EF system with Co-N-MoO₂/CF cathode has a potential for breaking metal-complex with good stability, showing that this cathode is a candidate for application for applications in EAPOs.

Removal of tyrosol from water by adsorption on carbonaceous materials and electrochemical advanced oxidation processes

This work compares the ability of physical and chemical treatments, namely adsorption and electrochemical advanced oxidation processes, to remove tyrosol from aqueous medium. Adsorption on graphene nanoplatelets (GNPs) performed much better than that with a graphite intercalation compound. Adsorption isotherms were found to follow the Freundlich model (R² = 0.96), which is characteristic of a chemisorption process. Successful electrochemical regeneration enables 5 successive adsorption/regeneration cycles before corrosion of GNPs occurs. Other typical aromatic contaminants that may coexist with tyrosol can be also adsorbed on GNPs. Percentage of regeneration efficiency of GNPs showed a higher affinity towards Lewis acids group compounds and a lower one towards Lewis base. The treatment of 100 mL of 0.723 mM tyrosol solutions in non-chlorinated and chlorinated matrices at pH 3.0 was carried out by electrochemical oxidation with electrogenerated H₂O₂ (EO-H₂O₂), electro-Fenton (EF) and UVA photoelectro-Fenton (PEF). Trials were made with a BDD anode and an air-diffusion cathode at 10-30 mA cm^-2. Hydroxyl radicals formed at the anode from water oxidation and/or in the bulk from Fenton's reaction between added Fe²⁺ and generated H₂O₂, along with active chlorine produced in chlorinated medium, were the main oxidants. Tyrosol concentration always decayed following a pseudo-first-order kinetics and its mineralization rose as EO-H₂O₂ < EF < PEF, more rapidly in the chlorinated matrix. The potent photolysis of intermediates under UVA radiation explained the almost total mineralization achieved by PEF in the latter medium. The effect of current density and tyrosol content on the performance of all processes was examined.

Low energy liquid plasma for direct reduction and formation of rGO-aminopyridine hybrid for electrical and environmental applications

The present works demonstrate the formation of reduced graphene oxide (r-GO) and aminopyridine (r-GO-(AmPy)_n) hybrid by submerged liquid plasma process. Raman spectra shows the ID/IG ratio of GO, r-GO and r-GO-(AmPy)_n are 2.2, 1.91 and 2.0, respectively. The decrease in ID/IG ratio of r-GO clearly indicate the reduction of oxygen functional groups and restoration of sp² network in r-GO domain. The pyridinic and pyrrolic functional group present in rGO-(AmPy)_n hybrids shows a distinct redox peaks in cyclic voltameter at the scan rates of 5, 10 and 25mV/s. The r-GO-(AmPy)_n hybrid displayed an excellent electrochemical performance with a high specific capacitance of 418, 400 and 381F/g at the current densities of 0.1, 0.2 and 0.3A/g, respectively. Electro chemical generation of H₂O₂ at the rGO-(AmPy)_n surface was evaluated and found to be 0.72mmol for the fixed reaction time of 60min. Similarly, conversion of H₂O₂ to OH radical with a coated Fe₃O₄ plate catalyst was found to be 0.15mmol. A H₂O₂/OH radicals generated in the electrochemical cell was used for the degradation of methyl parathion. During the degradation (7.5mg/L), two intermediates like methylparaoxon, and p-nitrophenol were identified by the Gas Chromatography and Mass Spectrometer analysis.

Study on preparation conditions of coal fly ash catalyst and catalytic mechanism in a heterogeneous Fenton-like process

The heterogeneous Fenton-like process catalyzed by H₂SO₄-modified coal fly ash can treat organic wastewater effectively.

Catalytic oxidation of organic pollutants in wastewater via a Fenton-like process under the catalysis of HNO3-modified coal fly ash

Organic wastewater can be treated effectively via a heterogeneous Fenton-like process under the catalysis of HNO₃-modified coal fly ash.