Electrochemical Electrode Research Articles

Simultaneous desalination and molecular resource recovery from wastewater using an electrical separation system integrated with a supporting liquid membrane

Separating molecular substances from wastewater has always been a challenge in wastewater treatment. In this study, we propose a new strategy for simultaneous desalination and selective recovery of molecular resources, by introducing a supported liquid membrane (SLM) with molecular selectivity into an asymmetric flow-electrode capacitive deionization. Salts and molecular substances in wastewater are removed after passing through the ion separation chamber and the molecular separation chamber, respectively. Faradaic reactions, i.e., the electrolysis of water with OH–, occurred in the electrochemical cathode electrode provides a sufficient and continuous chemical potential gradient for the cross-SLM transport of phenol (a model molecule substance). By optimizing the formulation of the liquid membrane and the pore size of the support membrane, we obtained the SLM with the best performance for separating phenol. In continuous experiment tests, the electrochemical membrane system showed stable separation performance and long-term stability for simultaneous salts removal and phenol (sodium phenol) recovery from wastewater. Finally, we demonstrate the potential application of this technology for the recovery of different carbon resources. Overall, the electrochemical system based on SLM is suitable for various wastewater treatment needs and provides a new approach for the recovery of molecular resources in wastewater.

Valorized pineapple waste by conventional and energy-saving ohmic extraction: potentially toxic elements and mycotoxin contamination

Pineapple peel is a food waste with environmental concerns. It can be valorized by extracting its bioactive compound through conventional and emerging technologies such as ohmic heating. However, mycotoxins and heavy metals contaminations could be concerns of such a valorization process. This study assessed the effects of conventional and ohmic heating on selected aflatoxins and metal ions in pineapple peel extract using high- performance liquid chromatography (HPLC) and inductively coupled plasma mass spectrometry (ICP-MS). Also, energy consumption and environmental impacts of the ohmic process were analyzed. According to the results, the ohmic-based valorization system reduced energy consumption and greenhouse gas emissions by more than 83%, contributing to net-zero and sustainable development goals (SDGs). Aflatoxins B1, B2, G1, and G2 were below the detection limit (B1, G1: 0.2µg/kg; B2, G2: 0.1µg/kg). However, ohmic extracts contained higher concentrations of Cr, Pb, Ni, and Fe because of electrochemical reactions and electrode corrosion. Despite the capability of ohmic valorization systems, inspecting food waste and valorized products for hazardous chemicals and investing in durable electrodes (e.g., titanium) are among the considerations for ohmic systems’ industrial implementation.

Cd2+ Detection by an Electrochemical Electrode Based on MWCNT-Orange Peel Activated Carbon.

This study reports the development of a new electrochemical sensor based on a carbon paste electrode (CPE) composed of biomass-based orange peel activated carbon (ACOP) and multiwalled carbon nanotubes (MWCNTs), and this composite is used for the electrochemical detection of cadmium ions (Cd2+). The ACOP/MWCNT composite was characterized by FTIR, Raman, and electrochemical impedance spectroscopy. The electrochemical evaluation of Cd2+ was performed using square wave and cyclic voltammetry. The ACOP/MWCNT-CPE electrochemical sensor exhibited a coefficient of determination r2 of 0.9907, a limit of detection of 0.91 ± 0.79 μmol L-1, and a limit of quantification of 3.00 ± 2.60 μmol L-1. In addition, the developed sensor can selectively detect Cd2+ in the presence of different interferents such as Zn2+, Pb2+, Ni2+, Co2+, Cu2+, and Fe2+ with a relative standard deviation (RSD) close to 100%, carried out in triplicate experiments. The ACOP/MWCNT-CPE presented high sensitivity, stability, and reproducibility and was successfully applied for the detection of Cd2+ in river water samples with recovery rate values ranging from 97.33 to 115.6%, demonstrating to be a very promising analytical alternative for the determination of cadmium ions in this matrix.

Co-MOF@GO nanotubes constructed from nickel foam loaded with Co(OH)2: A non-enzymatic high-performance electrochemical sensor for glucose

The construction and development of enzyme-free sensors made of non-precious metals that are extremely sensitive to glucose is of great importance for treatment of diabetes. A room temperature reaction method was used to grow ZIF-67@GO nanocubes on nickel foam substrates, followed by a hydrothermal method to construct Co(OH)2 nanomaterials. From this NF/ZIF-67@GO/Co(OH)2 enzyme-free glucose sensor with a unique structure was designed. The results and the charge transfer process of glucose's catalytic oxidation detection were systematically investigated in the composite material. The experimental results show that this sensor exhibits good electrochemical activity for glucose detection. It has a linear range of 0.1 μM-8.546 mM, a very high sensitivity of 2412.7 μA mM−1 cm−2, and its low detection limit is 0.934 M (signal-to-noise ratio of 3). These results indicate that the sensor is capable of accurately and sensitively detecting glucose concentration and has great potential for use in practical applications. The synthesis method is simple, fast, low-cost and easy to apply to electrochemical electrodes. Besides, the material has reproducibility, stability and good selectivity.

A Study on the O2 Plasma Etching Method of Spray-Formed SWCNT Films and Their Utilization as Electrodes for Electrochemical Sensors.

In this study, we analyzed the morphological changes and molecular structure changes on the surface of single-walled carbon nanotube (SWCNT) films during oxygen plasma (O2) etching of SWCNT surfaces formed by the spray method and analyzed their potential use as electrochemical electrodes. For this purpose, a SWCNT film was formed on the surface of a glass substrate using a self-made spray device using SWCNT powder prepared with DCB as a solvent, and SEM, AFM, and XPS analyses were performed as the SWCNT film was O2 plasma etched. SEM images and AFM measurements showed that the SWCNT film started etching after about 30 s under 50 W of O2 plasma irradiation and was completely etched after about 300 s. XPS analysis showed that as the O2 plasma etching of the SWCNT film progressed, the sp2 bonds representing the basic components of graphite decreased, the sp3 bonds representing defects increased, and the C-O, C=O, and COO peaks increased simultaneously. This result indicates that the SWCNT film was etched by the O2 plasma along with the oxygen species. In addition, electrochemical methods were used to verify the damage potential of the remaining SWCNTs after O2 plasma etching, including cyclic voltammetry, Randles plots, and EIS measurements. This resulted in a reversible response based on perfect diffusion control in the cyclic voltammetry, and an ideal linear curve in the Randles plot of the peak current versus square root scan rate curve. EIS measurements also confirmed that the charge transfer resistance of the remaining SWCNTs after O2 plasma etching is almost the same as before etching. These results indicate that the remaining SWCNTs after O2 plasma etching do not lose their unique electrochemical properties and can be utilized as electrodes for biosensors and electrochemical sensors. Our experimental results also indicate that the ionic conductivity enhancement by O2 plasma can be achieved additionally.

Is Ethanol Essential for the Lithium-Mediated Nitrogen Reduction Reaction?

The lithium-mediated nitrogen reduction reaction (Li-NRR) is a promising method for decentralized ammonia synthesis using renewable energy. An organic electrolyte is utilized to combat the competing hydrogen evolution reaction, and lithium is plated to activate the inert N2 molecule. Ethanol is commonly used as a proton shuttle to provide hydrogen to the activated nitrogen. In this study, we investigate the role of ethanol as a proton shuttle in an electrolyte containing tetrahydrofuran and 0.2 M lithium perchlorate. Particularly designed electrochemical experiments show that ethanol is necessary for a good solid-electrolyte interphase but not for the synthesis of ammonia. In addition, electrochemical quartz crystal microbalance (EQCM) demonstrates that the SEI formation at the onset of lithium plating is of specific importance. Chemical batch synthesis of ammonia combined with real-time mass spectrometry confirms that protons can be shuttled from the anode to the cathode by other species even without ethanol. Moreover, it raises questions regarding the electrochemical nature of Li-NRR. Finally, we discuss electrolyte stability and electrochemical electrode potentials, highlighting the role of ethanol on electrolyte degradation.

High utilization efficiency of tetramethylbenzoquinone hybridized in the pores of activated carbon for high-performance electrochemical capacitor electrodes

High utilization efficiency of tetramethylbenzoquinone hybridized in the pores of activated carbon for high-performance electrochemical capacitor electrodes

Redox electrochemistry of electrodes tuned with dimethyl ferrocene based on Co–NC–Pd nanogeometry: an impedimetric sensor for NADH sensing

Redox electrochemistry of electrodes tuned with dimethyl ferrocene based on Co–NC–Pd nanogeometry: an impedimetric sensor for NADH sensing

Van der Waals Interaction Mediated Redox on Graphene Electrode

Graphene, unlike (defective) graphene oxide, is generally not considered to be a highly efficient electrochemical electrode except for activity at the edges. This is because, graphene forms a highly stable hydration bilayer that screens the electric field emanating from the electrode to drive the electrochemical process. A remarkable electrochemical electrode property of graphene is discovered and explored. The property emerges from graphene’s single crystal, aromatic structure. The redox behavior of an aromatic compound, methylene blue (MB) and non-aromatic compounds, such as , potassium ferric cyanide are compared. The electrochemical behavior on monolayer of graphene is quantitatively measured by a novel opto-electrochemical instrument for both electrochemical and structural information. The instrument called, the Scanning Electrometer for electrical Double-layer (SEED) allows local measurement of redox on a 10 micron laser spot to exclusively measure redox signal away from the edges of graphene. Two distinct peaks for both reduction and oxidation during conventional cyclic voltametric (CV) waveform are observed by SEED (Figure 1). The two peaks were attributed to two distinct orientation of MB chemisorption on graphene and subsequent electron transfer. One of the peak depended on precise orientation of the MB on single crystal graphene surface indicating pi-pi interaction mediated chemisorption (Figure 2). The other peak is independent of graphene orientation. MB redox on Au showed a single peak (Figure 1) and was independent of orientation (Figure 2). The effect of the two modes of chemisorption on ionic strength was studied and compared with MB redox on pure gold performed on the same chip. The two peaks were not distinguishable by CV or differential pulse voltammetry (DPV) measured on the same sample under similar conditions. This indicated the sensitivity of SEED to obtain structural information and its ability to measure electrochemical activity on micro-spot. All the three measurements, SEED, DPV and CV were performed without taking the sample out of the solution. The redox of non-aromatic compounds showed no orientation effect. The distinct van der Waals interaction mediated chemisorption by pi-pi stacking on graphene electrode may have distinct advantage to design highly sensitive and specific sensors and biosensors in future, for example, in DNA and RNA sensing. Figure 1

Tracking Localized Degradation of Solid Oxide Cells Via Multi-Physics Modelling of Impedance Spectroscopy

The global, macro-scale description of degradation phenomena in solid oxide cells (SOC) reaches limitations when dealing with localized, micro-scale processes. For example, it is established that carbon deposition and transformation of the active area in nickel containing electrodes in electrolysis mode depend strongly on the local overpotential and gas composition. The state-of-the-art long-term characterization of a full SOC however relies on macroscopic measurements of DC polarization and electrochemical impedance spectroscopy (EIS), which are capturing the average response of the entire cell. The deconvolution of impedance spectra allows to separate the electrolyte resistance from electrode electrochemistry, gas conversion, and diffusion contributions. Nonetheless, heterogeneous, and local degradation cannot be described deploying commonly used tools of EIS analysis, such as equivalent electric circuit models, transmission line models, or the analysis of distribution of relaxation times.Multi-physics based numerical models on the other hand open new opportunities in gaining advanced insights into the complex degradation mechanisms in SOCs. In the model proposed here, combining simulations of transient and frequency domain into one framework allows the description of measured long-term durability of an SOC in terms of voltage-current and impedance characteristic. In addition, the framework enables a local, micro-scale description of the degradation process based upon physical properties confirmable in experiments.The modelling framework is validated with the durability measurements of the SOC in Sun et al. [1]. In this study, a fuel electrode supported cell with an active area of 16 cm2 was tested in galvanostatic operating conditions as an electrolysis cell with the constant current of -1 A/cm2 over 4383 h. Simultaneously to the voltage measurements over the test duration, the impedance response of the cell was tracked every eight hours. The evolution of the measured impedance spectra of the cell can be seen in the attached figure.Comparing the outcomes of the model to the experimental data showcases the benefits of the model in describing the degradation induced increase in voltage over time and the evolution of impedance spectra. In particular, the effect of higher activation overpotential at the fuel inlet to the outlet of the cell is analyzed enabling the generation of local insights concerning the observed degradation. The model establishes an improved validation of equations describing degradation of SOCs encompassing overpotential gradients and relating to postmortem observed micro-structural changes. Reference [1] Sun, X., et al. "Degradation in solid oxide electrolysis cells during long term testing." Fuel Cells 19.6 (2019): 740-747. Figure 1

From Ideal to Stack-like Contacting of an SOC

The cell performance of a solid oxide cell strongly depends on the testing environment and conditions. In case of an inert testing set-up with ceramic (Al2O3) flow fields and gold (cathode) and nickel (anode) contact grids the losses inside the cell determine the performance [1]. For an electrolyte-supported cell with a nickel / gadolinium-doped ceria (Ni/CGO) fuel electrode and LSCF air electrode, the ideal cell behavior has been characterized by electrochemical impedance spectroscopy (EIS) and the subsequent analysis of the distribution of relaxation times (DRT) considering technically meaningful operating conditions. Furthermore, the deconvolution and quantification of the gas diffusion polarization has been shown with the help of ternary fuel gas mixtures with different gas diffusion coefficients. [2-4]In this contribution, the electrochemical characterization is now extended to a stack-like contacting of the solid oxide cell with different metallic interconnectors, protective coatings and contact layers. The resulting contact loss is quantified with a method by Kornely et al. [5] using potential probes at the interconnector and the air electrode in order to enable voltage loss measurements. The stack-like contacting leads to gas transport conditions different from the ideal case which is investigated at the fuel and air side with modified gas diffusion coefficients by using gas mixtures containing nitrogen and helium as well [2].The positive effect of the protective coating towards the cell performance is evaluated by current-voltage characteristics and EIS measurements. Further, the electrode electrochemistry influenced by effects like chromium-poisoning will be shown and compared to the ideal contact set-up [2].

Two-step pyrolysis-hydrothermal synthesis of hierarchical nickel‑cobalt phosphate nanoflakes decorated on g-C3N4 nanosheets for high-performance hybrid supercapacitors

Ni-Co phosphate (NCP) nanoflakes and graphitic carbon nitride (g-CN) nanosheets are combined to fabricate a composite electrochemical electrode via a two-step pyrolysis-hydrothermal process. Physicochemical characterizations reveal the proper formation of the target material with highly porous morphology and crumpled nanostructures with highly active surface sites. The electrochemical properties of the NCP/g-CN composite in a three-electrode system depict excellent pseudocapacitive performance due to the faradaic behavior and redox activities of both NCP and g-CN with a very high capacitive value of 2000 F/g (242 mAh/g) @ 1 A/g current density. The charge storage behavior is mainly dominated by the surface-controlled (capacitive) process at higher scan rates, which is mostly dominated by surface pseudocapacitance, whereas, at low scan rates both surface-controlled and diffusion-controlled processes are equally active to provide a combined battery-capacitor behavior. Due to this, a hybrid supercapacitor device, fabricated with NCP/g-CN as positive and activated carbon (AC) as a negative electrode, showed excellent energy density (50 Wh/kg) along with exceptional cyclability (∼90 % capacity retention over 5000 cycles). Additionally, the redox-rich g-CN matrix within the composite dominates the sluggish diffusion-controlled process at higher scan rates to enhance the capacitive process without compromising the charge storage kinetics, thus enhancing the power density to ∼7.0 kW/kg. This excellent energy-power performance of the NCP/g-CN//AC hybrid supercapacitor cell (HSC) is better than some of the commercial devices like lead-acid, Ni-Cd, and Ni-MH batteries, indicating potential applications in next-generation charge storage devices.

Electrochemical supercapacitor based on polyaniline/bismuth-doped zinc oxide (PANI/Bi–ZnO) composite for efficient energy storage

The performance of high-rate supercapacitors is greatly controlled by the electrical and morphological properties of electrodes. Owing to its unique behavior, polyaniline (PANI) is considered one of the best materials for storing energy. This study emphasizes the fabrication of PANI and PANI/bismuth-doped zinc oxide (PANI/Bi–ZnO) as electrode materials for high-efficiency supercapacitors. The pure PANI and its composite were synthesized through inverse emulsion polymerization and investigated for structural and morphological characterization using UV/Vis spectroscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. These characterization techniques showed that the fabricated materials were suitable for supercapacitor electrodes with improved structural, thermal, and morphological properties. Electrochemical impedance spectroscopy, galvanostatic charging–discharging, and cyclic voltammetry were used to investigate the electrochemical properties. The PANI-based electrode showed ∼564.23 F/g charge storage capacity with ∼60% of capacitance retention, which correspondingly increased to ∼914.05 F/g and ∼88% in PANI/Bi–ZnO composite even after 10,000 charge–discharge cycles. The PANI/Bi–ZnO composite also displayed remarkably high energy density (∼2189.90 Wh/kg) and power density (∼38480.42 W/kg) values. The fabricated electrode is expected to have a large capacity for storing energy and power in commercial electrochemical electrodes.

Zeolitic Imidazolate Framework-Derived Zn/Co-S@Ni(OH)2 Nanoarrays with Excellent Energy Storage and Electrocatalytic Performance.

The design and development of high-performance electrochemical electrode materials are crucial for energy storage and conversion systems. This work reports a facile preparation of a self-supported Zn/Co-S@Ni(OH)2 array electrode in which a Zn/Co-S nanosheet is derived from a leaf-like zeolitic imidazolate framework (Zn/Co-ZIF-L). The core-shell structure provides multiple benefits such as enhanced electrical conductivity, an abundance of exposed active sites, and strong electronic interactions between Zn/Co-S and ultra-thin Ni(OH)2 nanosheets, facilitating faster charge transfer. Consequently, Zn/Co-S@Ni(OH)2 demonstrates remarkable electrochemical characteristics as an electrode material for supercapacitors with an area capacitance of 12.9 F cm-2 at a current density of 2 mA cm-2 in 2 M KOH. The assembled asymmetric supercapacitor device achieves a high energy density of 0.95 mW h cm-2, while showing excellent longevity with a retention of 90.9% over 5000 cycles. Additionally, the Zn/Co-S@Ni(OH)2 arrays demonstrate significant oxygen evolution reaction activity with an overpotential of 242 mV at 10 mA cm-2 in 1 M KOH and significant stability for more than 100 h. This work provides a valuable approach for synthesizing bifunctional electrode materials for both energy storage and electrocatalysis applications.

Green Prospective Approach of Chromium Zinc Oxide Nanoparticles for Highly Ultrasensitive Electrochemical Detection of Anti-hypotensive Medication in Various Matrices.

A highly ultrasensitive sensor that relied on Cr/ZnO-NPs was developed to detect etilefrine hydrochloride (ETF) in different matrices via a particular green voltammetric technique. The X-ray diffraction pattern showed the nanomaterials of the polycrystalline hexagonal structure. The energy-dispersive X-ray spectrum approved the presence of Cr3+ inside the host zinc oxide framework. The morphological and topological characteristics were visualized using transmission electron microscopy and atomic force microscopy micrographs describing the nanoparticles in spherical-like shape with large-surface area. The energy gap (Eg) was evaluated from transmittance (T %) and reflectance (R %) spectra within the visible region. The optimization study indicated that the Cr/ZnO-NP/CPE sensor has high sensitivity, thanks to the distinctive physical and chemical properties of the fabricated electrode. A new approach showed a great selectivity for determining ETF in different matrices in the presence of other interferents like levodopa. Under optimal circumstances, the square-wave voltammetry revealed a linear response to ETF from 0.01 to 10 μmol L-1 (r = 0.9996) with quantification and detection limits of 9.11 and 2.97 nmol L-1, respectively. Finally, the proposed approach was effectively applied to estimate ETF in pharmaceutical dosage forms and biological fluids using simple, accurate, and selective electrochemical electrode. The greenness profile assessment of the developed method was performed using the Eco-Scale and green analytical procedure index. These tools indicated that the proposed method is an eco-friendly technique for the determination of ETF in different matrices.

Electrochemical reservoir computing based on surface-functionalized carbon nanotubes

Reservoir computing, a type of neural network computing, is an energy-efficient and fast machine learning method, expected to realize low-power edge processing in sensor devices. This study constructs an electrochemical reservoir using carbon nanotube (CNT) thin-film electrodes on flexible plastic and proves the capability of the electrochemical functionalization of CNT thin films to improve the reservoir's performance. The performance of the time-series data prediction task, called the nonlinear autoregressive moving average (NARMA) task, can be improved using multiple CNT electrodes functionalized under different conditions. Based on the correlation coefficient analysis of the reservoir output, we illustrate that the reservoir dimensionality is enhanced by combining CNT electrodes with different functionalization conditions. Furthermore, the dimensionality and memory capacity of the reservoir can be improved using the displacement current of the electric double layer and the redox current in the electrochemical electrode. We demonstrate the time-series data prediction of blood glucose levels in patients with type 1 diabetes using a physical reservoir for the first time. The use of functionalized CNTs enables flexible and high-performance reservoir computing, leading to the low-power in-sensor edge processing of wearable sensors.

All-Optical Electrochemiluminescence.

Electrochemiluminescence (ECL) is widely employed for medical diagnosis and imaging. Despite its remarkable analytical performances, the technique remains intrinsically limited by the essential need for an external power supply and electrical wires for electrode connections. Here, we report an electrically autonomous solution leading to a paradigm change by designing a fully integrated all-optical wireless monolithic photoelectrochemical device based on a nanostructured Si photovoltaic junction modified with catalytic coatings. Under illumination with light ranging from visible to near-infrared, photogenerated holes induce the oxidation of the ECL reagents and thus the emission of visible ECL photons. The blue ECL emission is easily viewed with naked eyes and recorded with a smartphone. A new light emission scheme is thus introduced where the ECL emission energy (2.82 eV) is higher than the excitation energy (1.18 eV) via an intermediate electrochemical process. In addition, the mapping of the photoelectrochemical activity by optical microscopy reveals the minority carrier interfacial transfer mechanism at the nanoscale. This breakthrough provides an all-optical strategy for generalizing ECL without the need for electrochemical setups, electrodes, wiring constraints, and specific electrochemical knowledge. This simplest ECL configuration reported so far opens new opportunities to develop imaging and wireless bioanalytical systems such as portable point-of-care sensing devices.

Vertical Graphene-Based Printed Electrochemical Biosensor for Simultaneous Detection of Four Alzheimer's Disease Blood Biomarkers.

Early detection and timely intervention play a vital role in the effective management of Alzheimer's disease. Currently, the diagnostic accuracy for Alzheimer's disease based on a single blood biomarker is relatively low, and the combined use of multiple blood biomarkers can greatly improve diagnostic accuracy. Herein, we report a printed electrochemical biosensor based on vertical graphene (VG) modified with gold nanoparticles (VG@nanoAu) for the simultaneous detection of four Alzheimer's disease blood biomarkers. The printed electrochemical electrode array was constructed by laser etching and inkjet printing. Then gold nanoparticles were modified onto the working electrode surface via electrodeposition to further improve the sensitivity of the sensor. In addition, the entire printed electrochemical sensing system incorporates an electrochemical micro-workstation and a smartphone. The customized electrochemical micro-workstation incorporates four electro-chemical control chips, enabling the sensor to simultaneously analyze four biomarkers. Consequently, the printed electrochemical sensing system exhibits excellent analytical performance due to the large surface area, biocompatibility, and good conductivity of VG@nanoAu. The detection limit of the sensing system for Aβ40, Aβ42, T-tau, and P-tau181 was 0.072, 0.089, 0.071, and 0.051 pg/mL, respectively, which meets the detection requirements of Alzheimer's disease blood biomarkers. The printed electrochemical sensing system also exhibits good specificity and stability. This work has great value and promising prospects for early Alzheimer's disease diagnosis using blood biomarkers.

In-depth investigation on the self-catalyzed growth of W2N/In2O3 composite nanowires synthesized via nitrogen plasma assisted in-situ thermal annealing for boosting photoelectrochemical performance

Enhancing the charge separation efficiency through interface engineering of In2O3-based photoanodes represents a critical and complex research endeavor in the field of water splitting. Herein, we report a self-catalyzed growth of intrinsic Indium oxide (In2O3) Nanowires (NWs) and Tungsten nitride/Indium oxide (W2N/In2O3) composite nanowires (CNWs) on c-Si substrates by plasma assisted reactive thermal evaporation (PARTE) and nitrogen plasma assisted in-situ thermal annealing, respectively. The nitrogen plasma assisted in-situ thermal annealing effectively transforms the intrinsic In2O3 NWs to W2N/In2O3 CNWs. The optical energy gap, Eg gradually decreases from 2.49 to 2.40 eV when combine with W2N nanostructures. Decrease in the Eg simultaneously increases the photocurrent density of W2N/In2O3 CNWs at V = 0.4 V from 1.9 to 3.8 mA/cm2. This could attribute to the effective electron−hole separations at the interfaces of the heterojunction CNWs. The correlation between the substantially prolonged lifetime of charge carriers and narrowing the bandgap of the composite NWs could be feasible as a good electrochemical electrode. Moreover, the self-catalyzed and secondary growth mechanisms of hierarchically branched In2O3 NWs and W2N/In2O3 CNWs are discussed.

Electrochemical treatment of wastewater containing urea-formaldehyde and melamine-formaldehyde

The wastewater containing urea-formaldehyde (UF) and melamine-formaldehyde (MF) from the medium-density fiberboard (MDF) lamination factory disposed into the waterbodies adversely affects human health and aquatic life. Therefore, its treatment before discharge is necessary. Researchers have used various techniques to treat this type of wastewater in the past, but none have tried electrochemical (EC). However, EC can potentially remove pollutants such as chemical oxygen demand (COD), total organic carbon (TOC), formaldehyde (FA), total nitrogen (TN), nitrogen nitrate (NO3–N), and other hydrocarbons. Hence, this study uses the EC technique to treat wastewater containing UF and MF with aluminium electrodes. The experiments were run in batch mode with a 250 mL working volume in a 500 mL Pyrex glass beaker using a variable DC power supply (0–30 V and 0–5 A). The impacts of various parameters, including reaction time (RT) 30–240 min, current density (CD) 8.66–51.94 mA/cm2, inter-electrode distance (IED) 1–2 cm, and mixing speed in the range of 60–120 rpm were examined to achieve the best pollutant removals. The best removal percentage was reached at the optimized conditions of 150 min RT, 43.28 mA/cm2 CD, 1.5 cm IED, and 80 rpm: 81.1% TOC, 61.5% COD, 76.7% TN, 28.3% NO3–N, and 55.2% FA. During the EC process, electrodes and energy consumption were estimated at around 2.367 (g/L) and 0.18 (kWh/L), respectively. A kinetic analysis was also carried out to determine the pollutant's removal trend. This study concluded that the pseudo-first-order kinetic model was the best fit for removing TOC and FA with regression coefficients of 0.96 and 0.83, respectively.