Boron-doped Diamond Research Articles

Gallium Nitride Electrodeposition at Indium Tin Oxide and Fluorine Tin Oxide Electrodes in Ammonium Nitrate and Gallium Nitrate Aqueous Solution

The potential of gallium nitride thin films in semiconductor technology and devices has garnered interest. This study aims to develop an effective GaN electrodeposition technique that will function on both Earth and microgravity situations and may be applied to any kind of needed application, such as in photovoltaic devices. To determine the optimal electrodeposition conditions, e.g. applied potential, cyclic voltammetry (CV) was done on a boron-doped diamond electrode at 0.01 mV/s potential scan rate and at 0.8 V vs. Ag/AgCl (Saturated KCl) constant applied potential. In the CV study, a well-defined peak formed at -1.75 V vs. Ag/AgCl (Saturated KCl). To start examining all the features of the electrodeposition of a thin film on Indium Tin Oxide (ITO) and Fluorine Tin Oxide (FTO) Electrodes, chronoamperometry (CA) measurements were done at different time scales, ranging from 3600s to 14400s and at a constant applied potential of -1.7 V vs. Ag/AgCl (Saturated KCl). The characterization methods used to examine the materials' topography, elemental contrast, crystal structure, and electrodeposition weight percentages included scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). Longer electrodeposition times produced the best grain formation, promoting dendritic structure at the electrode surface. Furthermore, the optimal weight electrodeposition percentage of Ga and N was 10% and 35 % at 3600s, respectively, although the electrodeposited electrode surface was heterogeneous. The surface topographies at 3600s showed less grains definition and dendritic structures. At higher electrodeposition times, e.g. 14400s, more grain definitions and dendritic structures were found. For the 3600s electrodeposition time, XRD peaks were found at 33o, 37o and 46o, which are characteristics of GaN wurtzite structure according to literature.

Electrocatalytic oxidation of hexafluoropropylene oxide homologues in water using a boron-doped diamond electrode

ABSTRACT Hexafluoropropylene oxide (GenX) is a kind of substitute to PFOA, which has been listed in the Stockholm Convention. In this study, GenX was attempted to be degraded using a boron-doped diamond anode in the electrochemical oxidation system. The effects of operating parameters, including current density (0.5–10 mA/cm2), initial pH (3.0–11.49), initial concentration of GenX (20–150 mg/L), electrode distances (0.5–2 cm), electrolyte types (Na2SO4, NaCl, NaNO3 and NaHCO3) and Na2SO4 electrolyte concentration (40–80 mm), on GenX were studied. GenX can almost completely be degraded under the optimal operating parameters after 180 min of electrolysis. Free radical quenching experiments were carried out to investigate the effects of hydroxyl radicals and sulphate radicals on the degradation of GenX. The degradation intermediates were identified based on the ultra-high performance liquid chromatography equipped with a tandem mass spectrometer, and the degradation mechanisms were also proposed. Finally, the toxicities of GenX and its degradation products were evaluated using the QSAR models. The novelty is that the degradation mechanisms of the high concentration GenX (100 mg/L) were elucidated based on the free radical quenching experiments and the intermediates detected, when the degradation ratio reached 100%.

Ammonia Synthesis from Electrochemical Reduction of Nitrate Using Boron-Doped Diamond Electrodes

Ammonia Synthesis from Electrochemical Reduction of Nitrate Using Boron-Doped Diamond Electrodes

Eco-friendly solvent-based liquid-liquid extraction of phenolic acids from winery wastewater streams

This study proposes liquid-liquid extraction (LLE) for the recovery of phenolic acids from winery wastewater replacing common volatile organic compounds (VOCs) with environmentally friendly solvents. On one hand, terpenes (α-pinene and p-cymene) and terpenoids (eucalyptol and linalool) were selected as green solvents and compared to common VOCs (ethyl acetate or 1-butanol). On the other hand, gallic acid (GA), vanillic acid (VA), syringic acid (SA) and caffeic acid (CA) were selected as phenolic acids to be recovered. The extraction performance was evaluated under different operation conditions: solvent-to-feed ratio, initial concentration of phenolic acids and temperature.This work also evaluated the back-extraction whole process global recovery and solvent regeneration, by means of aqueous NaOH solution. Eucalyptol has shown the highest overall global extraction performance (21.07 % for GA, 93.21 % for VA, 78.79 % for SA, and 80.57 % for CA) and lower water solubility compared to the best performing VOC solvent (1-butanol). Therefore, eucalyptol can be a potential eco-friendly solvent to replace VOCs for sustainable phenolic acid recovery from winery wastewater. Finally, to ensure a clean water stream after the LLE, the traces of solvent were completely removed by electrooxidation with boron-doped diamond anode at a current density of 422.54 A/m2.

3-Methyl Thiophene-Modified Boron-Doped Diamond (BDD) Electrodes as Efficient Catalysts for Phenol Detection-A Case Study for the Detection of Gallic Acid in Three Specific Tea Types.

Polymer modification has been established as a cost-effective, simple, in situ method for overcoming some of the inherent disadvantages of boron-doped diamond (BDD) electrodes, and its application has been extended to reliable, low-cost environmental monitoring solutions. The present review focuses on modifying BDD electrodes with semi-conductive polymers acting as redox mediators. This article reports on the development of a 3-methyl thiophene-modified boron-doped diamond (BDD/P3MT) sensor for the electrochemical determination of total phenolic compounds (TPCs) in tea samples, using gallic acid (GA) as a marker. GA is a significant polyphenol with various biological activities, making its quantification crucial. Thus, a simple, fast, and sensitive GA sensor was fabricated using the electroanalytical square wave voltammetry (SWV) technique. The sensor utilizes a semi-conductive polymer, 3-methyl thiophene, as a redox mediator to enhance BDD's sensitivity and selectivity. Electrochemical synthesis was used for polymer deposition, allowing for greater purity and avoiding solubility problems. The BDD/P3MT sensor exhibits good electrochemical properties, including rapid charge transfer and a large electrochemical area, enabling GA detection with a limit of detection of 11 mg/L. The sensor's response was correlated with TPCs measured by the Folin-Ciocalteu method. Square wave voltammetry (SWV) showed a good linear relationship between peak currents and GA concentrations in a wide linear range of 3-71 mg/L under optimal conditions. The BDD/P3MT sensor accurately measured TPCs in green tea, rooibos tea, and black tea samples, with green tea exhibiting the highest TPC levels. The results demonstrate the potential of the modified BDD electrode for the rapid and accurate detection of phenolic compounds in tea, with implications for quality control and antioxidant activity assessments. The prolific publications of the past decade have established BDD electrodes as robust BDD sensors for quantifying polyphenols. Fruits, vegetables, nuts, plant-derived beverages such as tea and wine, traditional Eastern remedies and various herbal nutritional supplements contain phenolic chemicals. The safety concerns of contaminated food intake are significant health concerns worldwide, as there exists a critical nexus between food safety, nutrition, and food security. It has been well established that green tea polyphenol consumption promotes positive health effects. Despite their potential benefits, consuming high amounts of these polyphenols has sparked debate due to concerns over potential negative consequences.

Electrochemical Detection of Melatonin at Nano-Sized Highly Boron-Doped Diamond Electrode

This work investigates the electrochemical oxidation of melatonin at boron-doped diamond electrodes and demonstrates the significant enhancement in the detection of melatonin using highly boron-doped diamond nanopowder (h-BDD). Employing differential pulse voltammetry, Tween-coated h-BDD modified screen-printed electrodes (Tween/h-BDD/SPE) showed two linear response ranges for melatonin: 0.057–10 and 10–200 μM, with sensitivities of 390 ± 36 and 72.2 ± 3.4 μA mM–1, respectively, and a detection limit (3Sb/m) of 0.017 μM. The Tween/h-BDD/SPE demonstrated good selectivity against common interferences such as tryptophan, serotonin, lactate, cytidine, cytosine, and urea. The analytical utility of Tween/h-BDD/SPE was validated by quantifying melatonin in commercial pharmaceutical tablets, achieving close to 100% recoveries.

Electrochemical oxidation of Fe (II) using chlorpromazine drug at boron-doped diamond electrode: application to in vivo mechanism study interaction of chlorpromazine on hemoglobin iron and evaluation of some biomolecules

In this study, the electrochemical properties of aqueous chlorpromazine hydrochloride (CPZ) in the presence of Fe (II) were investigated by cyclic voltammetry at a boron-doped diamond (BDD) electrode. The results showed that an EC′ reaction mechanism occurs, where electrochemically generated CPZ species (cation radical) are reduced by Fe (II) back to the parent CPZ, and Fe (II) is oxidized to Fe (III). The detection limit, sensitivity, and dynamic concentration ranges were 2.8 μM, 0.0188 μA μM−1 and 10–166 μM. Based on the electrochemical results, the interaction of chlorpromazine (CPZ), a widely used antipsychotic tranquillizer, with the allosteric protein, hemoglobin, has been studied. First, four groups of six female rats weighing 400–450 g were selected. The rats were injected with different concentrations of chlorpromazine over a 3-week period, and the concentrations of hemoglobin, methemoglobin, red blood cells (RBCs), and hematocrit (HCT) were analyzed in the blood of each rat. After injection of different concentrations of the drug, the amount of hemoglobin) as a source of Fe (II)) decreased, but the amount of methemoglobin (as a source of Fe (III) increased. In addition, UV spectroscopic measurements in the range of 200–700 nm indicate the conversion of hemoglobin to methemoglobin in chlorpromazine-treated rats compared to the normal sample, and there was a direct relationship between the increasing methemoglobin concentration of chlorpromazine. Furthermore, the amount of RBC and HCT was measured. The results showed that RBC (21.05%–56.52%) and HCT (10.04%–53.19%) decreased. Finally, this study demonstrates a new mechanism for the effects of CPZ on hemoglobin iron in rat blood based on electrochemical results.

Understanding the Decamethylferrocene FeIII/IV Oxidation Process in Tris(pentafluoroethyl)trifluorophosphate-Containing Ionic Liquids at Glassy Carbon and Boron-Doped Diamond Electrodes.

Under voltammetric conditions, the neutral decamethylferrocene ([Me10Fc]) to cationic ([Me10Fc]+) FeII/III process is a well-known reversible outer-sphere reaction. A companion cationic [Me10Fc]+ to dicationic [Me10Fc]2+ FeIII/IV process has been reported under direct current (DC) cyclic voltammetric conditions at highly positive potentials in liquid SO2 at low temperatures and in a 1.5:1.0 AlCl3/1-butylpyridinium chloride melt. This study demonstrates that in room-temperature ionic liquids containing the hard to oxidize and hydrophobic tris(pentafluoroethyl)trifluorophosphate anion, the [Me10Fc]+/2+ process can be detected as a quasi-reversible reaction at glassy carbon (GC) and boron-doped diamond (BDD) electrodes. Large amplitude Fourier-transformed alternating current (FT-AC) voltammetry minimizes background current contributions occurring at potentials similar to those of the FeIII/IV process in the second and higher-order harmonics. This enables a straightforward determination of the thermodynamics and kinetics for both the FeII/III and FeIII/IV processes. Unlike the ideal outer-sphere FeII/III process, the parameters of the FeIII/IV process may be impacted by ion-interaction effects. For the faster FeII/III process, heterogeneous rate constants are approximately 10 times smaller at BDD than those at GC electrodes. This electrode dependence is less pronounced for the slower FeIII/IV process. The slower BDD kinetics may be attributed in part to a density of states lower than that at GC.

Novel approach to produce 3D boron-doped diamond for pollutant removal from water

Diamond growth from Chemical Vapor Deposition (CVD) on foreign substrates can require different pretreatment not only to improve the film nucleation but also to assure its adhesion by decreasing the expected film/substrate interface stress. To improve boron-doped film nucleation, growth, and adherence, different substrate pretreatments have been used mainly from the seeding process with diamond powder at various particle sizes. Despite this, the development of diamond growth on a Ti mesh remains difficult because of the requirement of a cohesive film to cover a 3D macroporous sample with varying growth rates based on its distinct network geometry. Then, this work describes a novel approach to growing boron-doped diamond (BDD) and boron-doped ultrananocrystalline diamond (B-UNCD) on titanium dioxide nanotubes (TDNT) produced simultaneously on both sides of Ti mesh by an anodization process. The films were obtained from two-step growth processes by assuring the entire diamond overlay on both TDNT/Ti mesh sides, including their outer/inner surfaces, as a 3D sample. TiO2 - TiC conversion has dominated the renucleation process, facilitating the nanometric scale control. The film morphologies were systematically analyzed by FEG-SEM images at different sample planes and depths for both sample sides at different stages of film growth. The unique morphology of titania nanotubes associated with columnar and/or renucleation development of BDD, considering the film defects and valley, can systematically increase the electrode specific area. Raman spectra showed the film quality and its micro and/or ultrananodiamond structure and the boron doping features. Also, this growth process allowed a dopant-controlled adjustable conductivity. Then, the boron doping levels for both films were evaluated from Mott-Schottky plots at around 1019 Bcm−3, characterizing them with good conductivity. In addition, electrochemical measurements from Cyclic Voltammetry (CV) confirmed the expected diamond response on redox pair following the quasi-reversible criteria as high-performance diamond electrodes and in situ Raman spectroelectrochemical measurements assessed the stability of samples during electrochemical measurements, ensuring structural integrity. Finally, the samples were applied to the degradation of methylene blue, proving to be superior materials for electrochemical applications due to their advantages compared to those of similar 2D electrodes.

What Are the Key Factors for the Detection of Peptides Using Mass Spectrometry on Boron-Doped Diamond Surfaces?

We investigated the use of boron-doped diamond (BDD) with different surface morphologies for the enhanced detection of nine different peptides by matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS). For the first time, we compared three different nanostructured BDD film morphologies (Continuous, Nanograss, and Nanotips) with differently terminated surfaces (-H, -O, and -F) to commercially available Ground Steel plates. All these surfaces were evaluated for their effectiveness in detecting the nine different peptides by MALDI-MS. Our results demonstrated that certain nanostructured BDD surfaces exhibited superior performance for the detection of especially hydrophobic peptides (e.g., bradykinin 1-7, substance P, and the renin substrate), with a limit of detection of down to 2.3 pM. Further investigation showed that hydrophobic peptides (e.g., bradykinin 1-7, substance P, and the renin substrate) were effectively detected on hydrogen-terminated BDD surfaces. On the other hand, the highly acidic negatively charged peptide adrenocorticotropic hormone fragment 18-39 was effectively identified on oxygen-/fluorine-terminated BDD surfaces. Furthermore, BDD surfaces reduced sodium adduct contamination significantly.

Boron-doped diamond electrodes: examining the effect of doping level on the degradation of pharmaceuticals

Boron-doped diamond electrodes: examining the effect of doping level on the degradation of pharmaceuticals

Electroanalytical sensing of antidiabetic drug linagliptin by using square-wave voltammetry on the boron-doped diamond electrode

Electroanalytical sensing of antidiabetic drug linagliptin by using square-wave voltammetry on the boron-doped diamond electrode

Spectral and microstructural analysis of the effect of the Ga+ implantation on diamond: a CL-EELS study

Due to its capacity to achieve nanometre-scale machining and lithography, a focused ion beam (FIB) is an extended tool for semiconductor device fabrication and development, in particular, for diamond-based devices. However, some technological steps are still not fully optimized for its use. Indeed, ion implantation seems to affect the crystalline structure and electrical properties of diamond. For this study, a boron-doped ([B] ∼ 1017 atoms·cm−3) diamond layer grown by chemical vapour deposition was irradiated using Ga+ by FIB, with 1 nA current and 5, 20, and 30 keV of acceleration voltage. The Ga+ implanted diamond layer has been analysed through cathodoluminescence (CL) and scanning transmission electron microscopy (STEM)-related techniques. The beam penetration depth has been simulated by Monte Carlo calculations of both Ga+ (FIB) and e− (CL) beams at different energies. The comparative CL analysis of the layer as-grown and after implantation revealed peaks related to defects, such as A band, H3 centre, and defects present in the green band region. The STEM studies for the 30 keV implanted sample showed that the diamond lattice is affected by the damage, evidencing amorphisation in the layer with a sp2/sp3 ratio of 1.37, estimated by electron energy loss spectroscopy. Therefore, this study highlights the effects of the Ga+ implantation on the optical and structural characteristics of diamond, using different methods.

Effect of electrolyte composition on electrocatalytic transformation of perfluorooctanoic acid (PFOA) in high pH medium

Recent regulatory actions aim to limit per- and polyfluoroalkyl substances (PFAS) concentrations in drinking water and wastewaters. Regenerable anion exchange resin (AER) is an effective separation process to remove PFAS from water but will require PFAS post-treatment of the regeneration wastestream. Electrocatalytic (EC) processes using chemically boron-doped diamond electrodes, stable in a wide range of chemical compositions show potential to defluorinate PFOA in drinking water and wastewater treatments. Chemical composition and concentration of mineral salts in supporting electrolytes affect AER regeneration efficiency, and play a crucial role in the EC processes. Their impact on PFAS degradation remains understudied. This study investigates the impact of 17 brine electrolytes with different compositions on perfluorooctanoic acid (PFOA) degradation in an alkaline medium and explores the correlation between the rate of PFOA degradation and the solution's conductivity. Results show that higher electrolyte concentrations and conductivity lead to faster PFOA degradation rates. The presence of chloride anions have negligible impact on the degradation rate. However, the presence of nitrate salts reduce PFOA degradation efficiency. Additionally, the use of mixed electrolytes may be a promising approach for reducing the cost of EC operations. PFOA degradation was not influenced by the pH of the bulk solution.

Evaluation of In Vitro Serotonin-Induced Electrochemical Fouling Performance of Boron Doped Diamond Microelectrode Using Fast-Scan Cyclic Voltammetry.

Fast-scan cyclic voltammetry (FSCV) is an electrochemical sensing technique that can be used for neurochemical sensing with high spatiotemporal resolution. Carbon fiber microelectrodes (CFMEs) are traditionally used as FSCV sensors. However, CFMEs are prone to electrochemical fouling caused by oxidative byproducts of repeated serotonin (5-HT) exposure, which makes them less suitable as chronic 5-HT sensors. Our team is developing a boron-doped diamond microelectrode (BDDME) that has previously been shown to be relatively resistant to fouling caused by protein adsorption (biofouling). We sought to determine if this BDDME exhibits resistance to electrochemical fouling, which we explored on electrodes fabricated with either femtosecond laser cutting or physical cleaving. We recorded the oxidation current response after 25 repeated injections of 5-HT in a flow-injection cell and compared the current drop from the first with the last injection. The 5-HT responses were compared with dopamine (DA), a neurochemical that is known to produce minimal fouling oxidative byproducts and has a stable repeated response. Physical cleaving of the BDDME yielded a reduction in fouling due to 5-HT compared with the CFME and the femtosecond laser cut BDDME. However, the femtosecond laser cut BDDME exhibited a large increase in sensitivity over the cleaved BDDME. An extended stability analysis was conducted for all device types following 5-HT fouling tests. This analysis demonstrated an improvement in the long-term stability of boron-doped diamond over CFMEs, as well as a diminishing sensitivity of the laser-cut BDDME over time. This work reports the electrochemical fouling performance of the BDDME when it is repeatedly exposed to DA or 5-HT, which informs the development of a chronic, diamond-based electrochemical sensor for long-term neurotransmitter measurements in vivo.

Electric Polarization-Dependent Absorption and Photocurrent Generation in Limnospira indica Immobilized on Boron-Doped Diamond.

We present the change of light absorption of cyanobacteria in response to externally applied electrical polarization. Specifically, we studied the relation between electrical polarization and changes in light absorbance for a biophotoelectrode assembly comprising boron-doped diamond as semiconducting electrode and live Limnospira indicaPCC 8005 trichomes embedded in either polysaccharide (agar) or conductive conjugated polymer (PEDOT-PSS) matrices. Our study involves the monitoring of cyanobacterial absorbance and the measurement of photocurrents at varying wavelengths of illumination for switched electric fields, i.e., using the bioelectrode either as an anode or as cathode. We observed changes in the absorbance characteristics, indicating a direct causal relationship between electrical polarization and absorbing properties of L. indica. Our finding opens up a potential avenue for optimization of the performance of biophotovoltaic devices through controlled polarization. Furthermore, our results provide fundamental insights into the wavelength-dependent behavior of a bio photovoltaic system using live cyanobacteria.

Towards an electrochemically-based circular economy: Electro-refinery for valorizing phenolic wastewater

This study introduces an innovative approach to wastewater treatment that combines two electrochemical technologies: electrolysis and electrochemical separation facilitated by anionic exchange membranes. This integrated technology converts pollutants into carboxylates, which are valuable intermediates for further electrosynthesis and fuel production. The efficacy of this approach was demonstrated using synthetic wastewater containing phenol as a model pollutant, chosen for its well-documented characteristics that enable comparative analysis with previous studies. The treatment process utilized mixed metal oxides (MMO) anodes with a composition of Ti/(RuO2)0.8(Sb2O4)0.2 and a boron-doped diamond (BDD) anode. The investigation was structured to evaluate each component of the treatment system individually before examining their collective performance. Through a series of case studies, the research not only confirmed the feasibility of this innovative technology but also highlighted the need for further study on the optimization of operational parameters and electrode materials. Comparative analysis revealed that MMO anodes outperformed BDD anodes, achieving maximum carboxylate transport rates of 138.7 mmol m−2h−1. The efficiency of carboxylate separation from the solution where they were generated reached up to 54.6 mmol kWh−1, while the maximum overall production efficiency was 8.77 mmol kWh−1. The study further determined that current density significantly affects both the production rate and the extent of mineralization, identifying optimal densities of 100 mA cm−2 and 30 mA cm−2 for the electrolyzer and electroseparator units, respectively. This work provides valuable insights for the optimization of this promising wastewater treatment technology, with potential applications in various industries.

Efficient electrochemical advanced degradation of Red CL and Red WB dyes from the tanning industry using a boron-doped diamond anode

Electrochemical oxidation (EO), electro-Fenton (EF), and photoelectro-Fenton (PEF) with a BDD anode have been comparatively assessed to remediate solutions of Red CL and/or Red WB azo dyes from real raw water. For the EO process in 50 mM Na2SO4 at pH 3.0, the main oxidant was the heterogeneous •OH generated at the anode, whereas in EF and PEF, the cathodic production of H2O2 and the addition of 0.50 mM Fe2+ catalyst additionally originated homogeneous •OH that enhanced the oxidation of organics. In PEF, the solution was illuminated with a 6 W UVA light. An almost total discoloration was always found operating with a 1:1 mixture of 200 mg L−1 of both dyes in 60 min, whose efficiency increased in the order of EO < EF < PEF. The HPLC analysis of the dye mixture treated by PEF disclosed that its degradation process agreed with its discoloration. A high 74% of COD was reduced due to the oxidative action of hydroxyl radicals and the photolysis of final Fe(III)-carboxylate species with UVA irradiation. The process was accompanied by an energy consumption of 0.76 kWh (g COD)−1, a value similar to the energy consumed by the applied UVA light.

Replacing oxygen evolution reaction in water splitting process by electrochemical energy-efficient production of high-added value chemicals with co-generation of green hydrogen

The utilization of biomass represents a promising alternative to the use of fossil fuels in facing both the energy problem and environmental pollution. Using the electrochemical oxidation of organic pollutants instead of the oxygen evolution reaction at the anode and the hydrogen evolution reaction at the cathode of an electrolyzer, it is possible to make high-value chemicals, break down pollutants, and produce hydrogen efficiently at the same time. In this study, the scale-up of the electrochemical treatment was investigated by treating technical cashew nutshell liquid effluent using a photovoltaic-driven electrochemical reactor with two compartments and equipped with a boron-doped diamond electrode as the anode and a Ni stainless-steel mesh as the cathode. Tests were carried out varying the anode current densities (40, 70, and 100 mA cm-2), the nature of the electrolyte solution (NaOH and Na2SO4), and the concentration of technical cashew nutshell liquid (0.01, 0.05, or 0.10 %). The results clearly shown that it is possible to successfully scale up a divided electrochemical reactor (passing from the batch approach of previous works to the flow approach of this study), favoring a selective accumulation of acetate (600 mg L-1) in the anodic compartment. In addition, the simultaneous production of green hydrogen (0.182 L h-1) was achieved when electrolyzing a biomass effluent containing 0.10 % technical cashew nutshell liquid in 1 mol L-1 NaOH and applying a current density of 40 mA cm-2. In conclusion, the sustainable electrochemical transformation of the waste (from technical cashew nutshell liquid into valuable products and energy carriers) was successfully achieved. We believe that the results will help the energy transition towards zero carbon emission and a cost-effective production of hydrogen through an integrated-hybrid process.

Electrochemically producing high-valent iron–oxo species for phenolics-laden high chloride wastewater pretreatment

Electrochemical advanced oxidation processes (EAOPs) have shown great promise for treating industrial wastewater contaminated with phenolic compounds. However, the presence of chloride in the wastewater leads to the production of undesirable chlorinated organic and inorganic byproducts, limiting the application of EAOPs. To address this challenge, we investigated the potential of incorporating Fe(II) and Fe(III) into the EAOPs with a boron-doped diamond (BDD) anode under near-neutral conditions. Our findings revealed that both Fe(II) and Fe(III) facilitated the generation of high-valent iron-oxo species (Fe(IV) and Fe(V)) in the anodic compartment, thereby reducing the oxidation contribution of reactive chlorine species. Remarkably, the addition of 1000 μM Fe(II) under high chloride conditions resulted in over a 2.8-fold increase in the oxidation rate of 50 μM phenolic contaminants at pH 6.5. Furthermore, 1000 μM Fe(II) contributed to a reduction of more than 66% in the formation of chlorinated byproducts, consequently enhancing the biodegradability of the treated water. Additionally, transitioning from batch mode to continuous flow mode further amplified the positive effects of Fe(II) on the EAOPs. Overall, this study presents a modified electrochemical approach that simultaneously enhanced the degradation of phenolic contaminants and improved the biodegradability of wastewater with high chloride concentrations.