Electrocatalytic Degradation Research Articles

Improving Stability of CO2 Electroreduction by Incorporating Ag NPs in N-Doped Ordered Mesoporous Carbon Structures.

The electroreduction of carbon dioxide (eCO2RR) to CO using Ag nanoparticles as an electrocatalyst is promising as an industrial carbon capture and utilization (CCU) technique to mitigate CO2 emissions. Nevertheless, the long-term stability of these Ag nanoparticles has been insufficient despite initial high Faradaic efficiencies and/or partial current densities. To improve the stability, we evaluated an up-scalable and easily tunable synthesis route to deposit low-weight percentages of Ag nanoparticles (NPs) on and into the framework of a nitrogen-doped ordered mesoporous carbon (NOMC) structure. By exploiting this so-called nanoparticle confinement strategy, the nanoparticle mobility under operation is strongly reduced. As a result, particle detachment and agglomeration, two of the most pronounced electrocatalytic degradation mechanisms, are (partially) blocked and catalyst durability is improved. Several synthesis parameters, such as the anchoring agent, the weight percentage of Ag NPs, and the type of carbonaceous support material, were modified in a controlled manner to evaluate their respective impact on the overall electrochemical performance, with a strong emphasis on operational stability. The resulting powders were evaluated through electrochemical and physicochemical characterization methods, including X-ray diffraction (XRD), N2-physisorption, Inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), SEM-energy-dispersive X-ray spectroscopy (SEM-EDS), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), STEM-EDS, electron tomography, and X-ray photoelectron spectroscopy (XPS). The optimized Ag/soft-NOMC catalysts showed both a promising selectivity (∼80%) and stability compared with commercial Ag NPs while decreasing the loading of the transition metal by more than 50%. The stability of both the 5 and 10 wt % Ag/soft-NOMC catalysts showed considerable improvements by anchoring the Ag NPs on and into a NOMC framework, resulting in a 267% improvement in CO selectivity after 72 h (despite initial losses) compared to commercial Ag NPs. These results demonstrate the promising strategy of anchoring Ag NPs to improve the CO selectivity during prolonged experiments due to the reduced mobility of the Ag NPs and thus enhanced stability.

Selective Electrocatalytic Degradation of Ether‐Containing Polymers

AbstractLeveraging electrochemistry to degrade robust polymeric materials has the potential to impact society's growing issue of plastic waste. Herein, we develop an electrocatalytic oxidative degradation of polyethers and poly(vinyl ethers) via electrochemically mediated hydrogen atom transfer (HAT) followed by oxidative polymer degradation promoted by molecular oxygen. We investigated the selectivity and efficiency of this method, finding our conditions to be highly selective for polymers with hydridic, electron‐rich C−H bonds. We leveraged this reactivity to degrade polyethers and poly(vinyl ethers) in the presence of polymethacrylates and polyacrylates with complete selectivity. Furthermore, this method made polyacrylates degradable by incorporation of ether units into the polymer backbone. We quantified degradation products, identifying up to 36 mol % of defined oxidation products, including acetic acid, formic acid, and acetaldehyde, and we extended this method to degrade a polyether‐based polyurethane in a green solvent. This work demonstrates a facile, electrochemically‐driven route to degrade polymers containing ether functionalities.

Selective Electrocatalytic Degradation of Ether-Containing Polymers.

Leveraging electrochemistry to degrade robust polymeric materials has the potential to impact society's growing issue of plastic waste. Herein, we develop an electrocatalytic oxidative degradation of polyethers and poly(vinyl ethers) via electrochemically mediated hydrogen atom transfer (HAT) followed by oxidative polymer degradation promoted by molecular oxygen. We investigated the selectivity and efficiency of this method, finding our conditions to be highly selective for polymers with hydridic, electron-rich C-H bonds. We leveraged this reactivity to degrade polyethers and poly(vinyl ethers) in the presence of polymethacrylates and polyacrylates with complete selectivity. Furthermore, this method made polyacrylates degradable by incorporation of ether units into the polymer backbone. We quantified degradation products, identifying up to 36 mol % of defined oxidation products, including acetic acid, formic acid, and acetaldehyde, and we extended this method to degrade a polyether-based polyurethane in a green solvent. This work demonstrates a facile, electrochemically-driven route to degrade polymers containing ether functionalities.

Three-dimensional Electrocatalytic Degradation of Tetracycline by Nano-Feooh

Nano-FeOOH catalysts were prepared by a co-precipitation method and characterized by XRD, SEM, XPS and BET to analyze the phase composition, surface morphology, elemental composition and specific surface area of FeOOH. Results showed that the FeOOH catalyst had large pore volume and surface area, providing more active sites for catalytic reactions. A 3D electrocatalytic system EC/PS/FeOOH was established to degrade tetracycline (TC), and the contributions of FeOOH adsorption, PS activation and electrocatalysis were investigated. It was found that the adsorption rate of TC on sole FeOOH was 42%, the degradation rate of TC in the PS/FeOOH system was 63.80%, and the degradation rate of TC in the 3D EC/PS/FeOOH system reached 72.97%, indicating the high electrocatalytic activity of FeOOH. Surface catalysis mechanism studies showed that the high catalytic activity of FeOOH could be attributed to electron transfer between Fe(II) and Fe(III) and adsorbed oxygen on its surface.

Electrocatalytic Degradation of Rhodamine B on the Sb-Doped SnO2/Ti Electrode in Alkaline Medium.

To realize efficient electrocatalytic degradation of organic compounds in alkaline wastewater, an Sb-doped SnO2/Ti electrode was fabricated and employed for the removal of Rhodamine B (RhB), and the electrocatalytic oxidation performance of this electrode was assessed in an alkaline medium. In an alkaline solution (pH 11), the complete fading of 50 mg·L-1 RhB could be achieved after 150 min of degradation, the removal efficiency of the chemical oxygen demand reached 56.1% at 300 min, and the degradation process of RhB followed the pseudo-first-order kinetic model very well. Under the attack of hydroxyl radicals, partial RhB was degraded to low-molecular-weight organic acids through N-demethylation and the destruction of the conjugated chromophore. Various techniques including scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and cycle voltammetry were used to examine the changes in the morphology and structure, as well as the activity of the Sb-doped SnO2/Ti electrode before and after use. The Sb-doped SnO2/Ti electrode could be reproduced in batches, and each electrode was reused up to eight times without a significant decrease in degradation ability; the leaching amount of antimony was significantly lower than the national emission standard. The electrocatalytic oxidation of the dye wastewater sample was also performed with the desired results, indicating that electrochemical oxidation is a very promising technology for the treatment of alkaline dye wastewater using a Sb-doped SnO2/Ti electrode.

Ultra-sensitive hexagonal wurtzite zinc oxide-based electrochemical sensor for specific recognition of environmental trace N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine

Emerging contaminant N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine has caused severe threats to ecosystems, necessitating the development of highly sensitive detection methods. Herein, a reliable and ultra-sensitive electrochemical sensor based on a carbon paste electrode modified by hexagonal wurtzite zinc oxide was developed for selective determination and degradation of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine. Experimental results demonstrated the successful application of the sensor for detecting N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine in soil samples. The contaminant contents were found to be 1.46–24.68 nmol L−1 in Zhengzhou City and 1.99–11.3 nmol L−1 in Pingdingshan City, respectively, along with a satisfactory recovery rate. Density functional theory calculations revealed that the hexagonal wurtzite zinc oxide crystal significantly decreased the activation energy of catalytic conversion compared to cubic sphalerite, resulting in a notable improvement in sensor response. Cryogenic electron microscopy technique further confirmed that the electrocatalytic degradation product of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine was not toxic N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone. Under optimal analysis conditions, the sensor achieved widely low as well as high linear ranges (0.1–800 nmol L−1 and 0.9–20 μmol L−1) with a low detection limitation (33 pmol L−1), indicating that such a highly sensitive and cost-effective electrochemical sensor has the potential for environmental pollutants monitoring.

Dimensionally Stable Ti-Based Ru–Ir Electrode Based Highly Efficient Electrocatalytic Degradation of Methamphetamine

Dimensionally Stable Ti-Based Ru–Ir Electrode Based Highly Efficient Electrocatalytic Degradation of Methamphetamine

A Diamond/Graphene/Diamond Electrode for Waste Water Treatment

Boron-doped diamond (BDD) thin film electrodes have great application potential in water treatment. However, the high electrode energy consumption due to high resistance directly limits the application range of existing BDD electrodes. In this paper, the BDD/graphene/BDD (DGD) sandwich structure electrode was prepared, which effectively improved the conductivity of the electrode. Meanwhile, the sandwich electrode can effectively avoid the degradation of electrode performance caused by the large amount of non-diamond carbon introduced by heavy doping, such as the reduction of the electrochemical window and the decrease of physical and chemical stability. The microstructure and composition of the film were characterized by scanning electron microscope (SEM), atomic force microscopy (AFM), Raman spectroscopy, and transmission electron microscopy (TEM). Then, the degradation performance of citric acid (CA), catechol, and tetracycline hydrochloride (TCH) by DGD electrodes was systematically studied by total organic carbon (TOC) and Energy consumption per unit TOC removal (ECTOC). Compared with the single BDD electrode, the new DGD electrode improves the mobility of the electrode and reduces the mass transfer resistance by 1/3, showing better water treatment performance. In the process of dealing with Citric acid, the step current of the DGD electrode was 1.35 times that of the BDD electrode, and the energy utilization ratio of the DGD electrode was 2.4 times that of the BDD electrode. The energy consumption per unit TOC removal (ECTOC) of the DGD electrode was lower than that of BDD, especially Catechol, which was reduced to 66.9% of BDD. The DGD sandwich electrode, as a new electrode material, has good electrochemical degradation performance and can be used for high-efficiency electrocatalytic degradation of organic pollutants.

Enhanced molecular oxygen activation via K/O interfacial modification for boosted electrocatalytic degradation over a broad pH range

Molecular oxygen activation plays an important role in the electrocatalytic degradation of recalcitrant pollutants. And the key lies in the tailoring of electronic structures over catalysts. Herein, carbon nitride with K/O interfacial modification (KOCN) was designed and fabricated for efficient molecular oxygen activation. Theoretical screening results revealed the possible substitution of peripheral N atoms by O atoms and the location of K atoms in the six-fold cavities of g-C3N4 framework. Spectroscopic and experimental results reveal that the existence of K/O promotes charge redistribution over as-prepared catalysts, leading to optimized electronic structures. Therefore, optimized oxygen adsorption was realized over 8 % KOCN, which was further converted into superoxide and singlet oxygen effectively. The rate constant of 8 % KOCN (1.8 × 10-2 min−1) reached 2.2 folds of pristine g-C3N4 (8.1 × 10-3 min−1) counterpart during tetracycline degradation. Moreover, the high electron mobility and excellent structural stability endow the catalyst with remarkable catalytic performance in a broad pH range of 3–11.

Adsorption synergy electrocatalytic degradation of phenol by active oxygen-containing species generated in Co-coal based cathode and graphite anode

Abstract The coal base electrodes and efficient coal base loaded cobalt electrodes (Co-CE) were prepared by pyrolysis method of low rank coal united activation method of KOH in order to develop more pores structures. The morphology of electrodes were characterized by Scanning electron microscopy, meanwhile, the type of elements were detected by energy dispersive spectroscopy (EDS). The electrochemical performance of electrodes were tested by cyclic voltammetry and electrochemical impedance spectroscopy. The lamella structures and pores were observed in microtopography of electrodes and the cobalt were successfully loaded in Co-CE from the EDS analysis. The operating conditions of processing time, current density, electrolyte concentration, pH and initial phenol concentration on this electrochemical system in single factor experiment were separately explored, correspondingly, the value was 180 min, 40 mA·cm−2, 0.01 mol·L−1, 2, 100 mg·L−1, and the phenol removal rate (R) were at the range of 47.64–67.84%. In the optimization experiment of JMP design, the removal rate could reach at 83.47%. The response surface methodology was employed for optimizing operation conditions to improve R. And the prediction model obtained for the response can be represented as: R = 66.5275 + 6.7311X 1 – 5.4197X 4 – 5.2303X 5 + 4.9555X 1 2 – 12.5219X 2 2 – 6.2912X 4 2 + 16.0937X 5 2 + 2.4109X 2 X 4 – 7.910X 3 X 4 – 3.0123X 3 X 5 – 2.183X 4 X 5. The optimized conditions were pH 3, 100 mg·L−1 of phenol concentration, 0.1 mol/L of electrolyte concentration, 35 mA/cm2 of current density, and 180 min of processing time. Meanwhile, the predicted R was 90.86%, the actual R of three parallel experiments were 91.2%, 89.3%, 91.05%, which were well consistent with the predicted value. Additionally, the degradation mechanism was proposed as that the adsorption in pore structures synergy electrocatalytic effect of Co-CE. Micro-electric fields formed in pores and the transition metal catalysis accelerated the transformation of cathode hydrogen peroxide to generate hydroxyl radical (·OH). Furthermore, the ·OH were produced both by cathode and anode which promoted the degradation of phenol. This high catalytic activity and low cost Co-CE is a kind of prospective electrode for electrochemical degradation of phenolic wastewater.

Ferroelectric BaTiO3@ZnO core-shell heterojunction triboelectric nanogenerators for electrochemical degradation of MO

The self-powered electrocatalyst based on the triboelectric nanogenerators (TENG) is an innovative idea, but the low output power density of TENG greatly hinders its vigorous development. Thus the improvement of output performance of TENG and the exploration of effective electrocatalytic degradation methods are still important task for the development of self-powered electrocatalyst. In the paper, the BaTiO3@ZnO (BTO@ZnO) core-shell heterogeneous nanocomposites have been successfully prepared by two steps of water bath and hydrothermal method, showing obvious ferroelectric properties and significantly improved dielectric properties compared with the pure ZnO and BaTiO3 nanostructures. Then, the prepared BTO@ZnO core-shell heterogeneous nanocomposites were embedded into polydimethylsiloxane (PDMS) matrix as triboelectric layer to assemble TENG. The introduction of BTO@ZnO core-shell heterojunctions greatly increases dielectric constant of triboelectric layer through the space charge polarization, and further significantly improve the output performance. Meantime, the mass ratios of BTO@ZnO in the triboelectric layer were further optimized, as the mass ratio of BTO@ZnO is 10 %, both the open circuit voltage (VOC) and short circuit current (JSC) attain the maximum values, even the output power density also attains to the maximum, and 13 LEDs or even more are lit instantaneously under a gentle hand tap. Lastly, the typical pollutant MO were added into NaCl solution, and the BTO@ZnO/PDMS-based TENG were successfully used to power the electrocatalytic degradation of MO. The strong oxidants of the superoxide hydroxyl radicals OH* and hypochlorite ClO− are continuously formed in the NaCl solution including MO to efficiently degrade the MO molecules.

Enhanced electrocatalytic degradation of acid orange 7 by using double perovskite La2CoxNi1-xMnO6/nickel foam as the electro-Fenton cathodes

Adequate generation of hydrogen peroxide and its subsequent activation into reactive oxygen species (ROS) play a crucial role in the catalytic efficiency of heterogeneous electro-Fenton for the degradation of contaminants. Herein, a series of La2NiMnO6 double perovskite with Co doping (La2CoxNi1-xMnO6) were prepared by a facile sol-gel technique and applied as catalysts in heterogeneous electro-Fenton system to removal acid orange 7 (AO7). Nickel foam was chosen as the supporting substrate for the catalyst owing to its excellent physical properties to accelerate the conversion of O2 to H2O2. La2Co0.5Ni0.5MnO6 achieved 90.22 % of AO7 decomposition rate at 120 min via the heterogeneous electro-Fenton system, which was a significant improvement over the catalytic efficiency of both only NF and La2NiMnO6 electrodes. Further studies have shown that the introduction of Co could heighten the efficient redox recycling of Ni2+/Ni3+ and Mn3+/Mn4+ on the electrode surface, synergically facilitating the conversion of H2O2 to OH. Meanwhile, the three redox pairs (Ni2+/Ni3+, Mn3+/Mn4+ and Co2+/Co3+) also stimulated the production of superoxide radicals (O2−), which was also not negligible in enhancing degradation. Finally, the possible pathway and mechanism of the degradation of AO7 were proposed. This work demonstrates that La2CoxNi1-xMnO6/NF has the potential to be a satisfactory electrode for decomposition of organic dyes in aqueous solution.

Effects of Rare Earth Doping on Structural and Electrocatalytic Properties of Nanostructured TiO2 Nanotubes/SnO2-Sb Electrode for Electrochemical Treatment of Industrial Wastewater

The solvothermal synthesis technique was employed to successfully fabricate a series of rare earth doped SnO2-Sb electrodes on the TNTs array substrate, serving as anode material for electrocatalytic degradation of phenol. The electrode doped with rare earth elements demonstrated superior electrocatalytic activity and stability in comparison to the undoped electrode. The influence of adding rare earth elements (i.e., Gd and Nd) into the precursor solution on the structural and property of TNTs/SnO2-Sb electrodes was studied in detail. The results obtained from SEM and XRD indicated that, compared to TNTs/SnO2-Sb-Nd, TNTs/SnO2-Sb-Gd exhibited a finer grain size due to the smaller ionic radius of the Gd element. This facilitated its incorporation into the SnO2 lattice interior and inhibited grain growth, resulting in a significant decrease in particle size for exposing more active sites. The influence mechanism of rare earth doping on electrochemical activity was investigated through XPS, EPR, LSV, EIS and Hydroxyl radicals (•OH) generation tests. The results demonstrated that the enhanced electrocatalytic activity can be attributed to an increased generation of oxygen vacancies on the electrode surface, which act as active sites for enhancing the adsorption of oxygen species and promoting •OH generation.

Electrochemically enhanced activation of Co3O4/TiO2 nanotube array anode for persulfate toward high catalytic activity, low energy consumption, and long lifespan performance

Advanced oxidation processes (AOPs) can directly degrade and mineralize organic pollutants (OPs) in water by generating reactive oxygen species with strong oxidizing ability. The development of advanced electrode materials with high catalytic performance, low energy consumption, no secondary pollution, and long lifespan has become a challenge that must be addressed in this field. A heterojunction catalyst loaded with Co3O4 on TDNAs (Co3O4/RTDNAs) was designed and constructed by a simple and efficient pyrolysis (Co3O4/TDNAs) and electrochemical reduction. Co3O4 can be uniformly distributed on the inner wall and surface of the TiO2 nanotubes, enhancing the specific surface area while forming a tight conductive interface with TiO2. This facilitates rapid transmission of electrons, thereby assisting Co3O4 in quickly activating PS to form reactive oxygen species. The Ti3+ and Ov generated in Co3O4/RTDNAs can significantly improve the electrocatalytic degradation of OPs. Also, the interface formed by Co3O4 and RTDNAs will effectively suppress Co2+ leakage, thereby reducing the risk of secondary pollution. When the reaction conditions were 1 mM PMS (PDS) and a current density of 5 mA/cm2 in the EA-PMS (PDS)/Co3O4/RTDNA system, 30 mg/L TC can achieve 83.24 % (81.89 %) removal in 120 min, with very low cobalt ion leaching, while the energy consumption was reduced significantly. Therefore, EA-PS/Co3O4/RTDNA system has strong stability and a high potential for treating the OPs in AOPs.

Zero-dimensional N-doped carbon quantum dots and palladium co-modified titanium electrodes enhance the electrocatalytic degradation of oxytetracycline hydrochloride

Reducing the amount of precious metals and improving their catalytic activities are difficult problems in the field of electrocatalysis. In this study, Pd/N-CQDs/Ti electrodes were prepared by introducing the N element into zero-dimensional carbon quantum dots and then compounded with Pd metal, and the electron transfer mechanism was explored. The results showed that the composite electrode degraded OTC up to 90.41% (60 min) at natural pH with an energy consumption of only 0.288 kWh/m3. The Pd/N-CQDs/Ti electrode formed a Pd-N-CQDs interface due to the electronic metal-carbon interaction (EMCI). In this, electrons are transferred from Pd to N, and the Pd-N interface plays a major role in hydrogen precipitation and the generation of atomic hydrogen. The generated H* ,·OH, and HClO all contribute to the degradation of OTC. According to the cycling experiments, the Pd/N-CQDs/Ti electrode showed good stability. When applied to OTC degradation in real water bodies, good reactivity was still maintained. Toxicity assessment of the degradation intermediates by ECOSAR and TEST showed that the electrode could effectively reduce the biotoxicity of OTC. In this study, the interface of the catalytic electrode was tuned to enhance its intrinsic activity, which provides an efficient strategy for electrocatalytic remediation of antibiotic contamination.

Leachate xenobiotics electrocatalytic degradation and simultaneous carbon quantum dots synthesis for anti-counterfeiting applications

The leachate treatment and the management of sludge after its treatment is a big challenge due to its many toxins and pollutants. The novelty of the current work resides in our attempt to address both difficulties by treating the leachate with electrofenton using low-cost stainless steel electrodes, followed by converting the sludge generated into quantum dots suited for anti-counterfeiting applications. On the electrofenton treatment of leachate, at the optimized conditions, the percentage removal of total organic carbon (TOC), UV254, chemical oxygen demand (COD), and NH3-N was found to be 79 %, 93 %, 90 %, and 90 % respectively with less energy consumption of 0.26 KWh/KgCOD. The gas chromatography-mass spectroscopy (GC–MS), 3D fluorescence spectroscopy matrix, and UV–Vis analysis confirmed the removal of xenobiotics and dissolved organic matter (DOM). The carbon quantum dots (S-CQDs) synthesized from sludge were characterized for X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transforms infrared spectroscopy (FTIR), PL intensity (Photoluminescence), and UV–Vis. The S-CQDs are very promising in qualitative fingerprint image enhancement in terms of overall pattern, dots, and ridges and are well suited as an alternate, efficient, green anticounterfeiting material. Thus, highly polluted leachate was efficiently treated and sludge was converted into useful carbon dots with the anti-counterfeiting application.

Optimized electrocatalytic degradation of ciprofloxacin using Co3O4 coated stainless steel electrodes

Ciprofloxacin (CIP) is a fluoroquinolone antibiotic that is widely used across the globe and its release is a serious concern due to its persistent nature, partial degradation, and simple transport through different environmental matrices. Pharmaceuticals have been degraded effectively by electrochemical oxidation. Exploring ways to increase the mineralization of these compounds while maintaining low power consumption is important. In this study, the treatability and degradation of CIP were investigated by using cobalt oxide-coated stainless steel (SS) electrodes in a lab-scale electrochemical (EC) reactor. The performance of the electrochemical reactor was determined under various operational conditions. The feed wastewater was synthetically prepared in the laboratory with varying concentrations of CIP ranging from 8 to 41 mg/L and the EC reactor was operated with an applied voltage and airflow rate of 2.6–9.3 volts and 1.6–3.5 L/min, respectively. A 3-factor central composite experimental design (CCD) was developed by using response surface methodology (RSM) in Design-Expert software. At a residence time of 27 min, initial concentration of 25 mg/L, airflow rate of 2.5 L/min, and applied voltage of 6 volts, the EC reactor achieved a removal efficiency of 70.8% for CIP with SS electrodes. On the contrary, the removal efficiency was increased to 91.5% at a reduced residence time of 21 min with cobalt oxide (Co3O4) coated over SS plates. The results indicated that Co3O4@SS electrodes resulted in better removal efficiency of CIP at a lower residence time. This system can be used as a robust benchmark for a single or consortium of antibiotics present in domestic and hospital wastewater.

Boosted electrocatalytic oxidation of organophosphorus pesticides by a novel high-efficiency CeO2-Doped PbO2 anode: An electrochemical study, parameter optimization and degradation mechanisms

This article presents a novel and highly efficient electrocatalytic degradation method for two significant organophosphorus pesticides, fenitrothion (FEN), and methyl parathion (MPN), using a Ti/β-PbO2-CeO2 modified anode (indirect oxidation). A comprehensive electrochemical investigation was also carried out to gain new insight into the redox behavior and destruction pathway of these pesticides (direct oxidation). The study also explores the effects of various operating parameters, such as initial solution pH, applied current density, and initial pesticides concentration, on the conversion-paired electrocatalytic removal process. To further enhance the degradation efficiency, a new configuration of the electrochemical cell was designed, employing two types of electrodes and two independent power supply devices. The conversion paired electrocatalytic degradation process of these pesticides involves first the direct reduction of FEN (or MPN) on a graphite cathode and then the indirect oxidation of reduced FEN (or MPN) by hydroxyl radicals electro generated on the Ti/β-PbO2-CeO2 anode. The synergism of these two processes together will effectively lead to FEN (or MPN) degradation. The degradation percentages of 98% for FEN and 95% for MPN at the optimal conditions for the electrochemical degradation of these pesticides were achieved at pH = 7, initial concentration 50 mg L−1, with a current density of 90 mA cm−2 for direct reduction and 11 mA cm−2 for indirect oxidation. Overall, this study presents a promising and efficient approach for the remediation of organophosphorus pesticide-contaminated environments, offering valuable insights into the electrochemical degradation process and highlighting the potential for practical application in wastewater treatment and environmental protection.

Electrocatalytic degradation of nitrogenous heterocycles on confined particle electrodes derived from ZIF-67

Nitrogen-containing heterocyclic compounds (NHCs) are hazardous, toxic, and persistent pollutants, thereby requiring urgent solutions. Herein, ZIF-67 was compounded with powder-activated carbon (PAC) to prepare Co/NC/PAC (NC i.e. nitrogen-doped carbon) particle electrodes for the electrocatalytic treatment of pyridine and diazines. Co/NC/PAC reflected the confinement of Co3O4/CoN/Co0 into the N-doped graphitic-carbon layer to generate both pyrrolic-N and graphitic-N active sites. Under the optimal conditions (0.3 A, 12 mL min−1, and initial pH 7.00), the degradation of four NHCs realized 90.2–93.7% efficiencies. The number and position of N atoms in NHCs directly affected the degradation efficiency. The following increasing order of facilitated degradation was recorded: pyridazine < pyrimidine < pyrazine < pyridine. The as-obtained Co/NC/PAC possessed the direct redox effect on NHCs, achieving fast electrocatalytic rate. Species like ·OH and H* were detected in Co/NC/PAC system with contributions to NHCs degradation estimated to 24% and 34%, respectively. Density functional theory (DFT) calculations revealed H* susceptible to attacking the N position, while the meta-position of C was subject to hydroxyl radical (·OH) addition. Overall, degradation of NHCs was achieved by hydro-reduction, oxidation, ring opening cleavage, hydroxylation, and mineralization. Ring-cleavage and mineralization of NHCs provided a novel electrochemical strategy to refractory wastewater treatment.

Electrocatalytic degradation of p-nitrophenol on metal-free cathode: Superoxide radical (O2•−) production via molecular oxygen activation

Although metal-free electrodes in molecular oxygen-activated Fenton-like wastewater treatment technologies have been developed, the reactive oxygen species (ROS) generation mechanisms are still not sufficiently clear. As a typical example of refractory phenolic wastewater, p-nitrophenol (PNP) has been widely studied. This study demonstrated the critical role of superoxide radicals (O2•−) in PNP degradation by metal-free electrodes through electron spin resonance (ESR), ROS quenching, and density functional theory (DFT) tests. The most superior metal-free electrode exhibited a mass activity of approximately 133.5 h−1 gcatalyst−1. Experimental and theoretical studies revealed the mechanism of O2•− generation via oxygen activation, including one- and three-electron transfer pathways, and found that O2•− mainly attacked the nitro group of PNP to degrade and transform the pollutant. This study enhances the mechanistic understanding of metal-free materials in the electrochemical degradation of refractory pollutants.