关键词： Nozzles  

摘要： In hybrid laser-electrochemical micromachining, both laser and electrochemical process energies act along the same machining axis and thus both influence material removal by their interaction. The traditional nozzle based laser assisted jet-ECM concepts require laser to be focused on workpiece surface in an electrochemical environment and are limited in aspect ratios as the nozzle stays above the workpiece surface. In this work, a hybrid tooling concept is proposed for a novel process scheme of precision hybrid laser-electrochemical micromachining. The tool serves the function of both an ECM electrode as well as a leaky-type multimode waveguide for the laser and delivers laser homogeneously together with the electrolyte on the workpiece surface without requiring laser to be focused on the workpiece surface. A precision prototype hybrid machine-tool is developed which employs short pulsed nano-second laser and micro-second pulsed voltage source for precision micromachining. For this system, ray tracing and detailed multiphysics electrochemical micromachining process simulations are carried out to demonstrate the applicability of this hybrid tooling concept and explain the shape evolution. Successful experimental realization of coaxial and concurrent application of electrochemical and laser processes is presented. Prototype tool electrodes are fabricated and experiments are carried out on an in-house developed prototype hybrid machine tool. The results reveal that the proposed hybrid tool is successfully capable of concentrating laser and electrochemical process energies simultaneously in the same machining zone. However, with the initial design of this hybrid tool, a maximum of 30-40% of laser power is available in the machining zone. Some suggestions for further research will be presented.

关键词： Ferro-cerium oxide   Nanocomposite   Sol-gel combustion method   Cadmium ions   Square wave anode stripping voltammetry  

摘要： Cd(II) is a biologically active element that requires rapid and reliable monitoring for its pollution control. We designed the electrochemical sensing nanocomposite with enhanced adsorption followed by redox processes, which was synthesized by incorporating ferric ions into cerium oxide substrate (hereafter CeFe2O5) via the sol-gel combustion method. The CeFe2O5 nanocomposite modified glassy carbon electrode (CeFe2O5/GCE) was used for selective detection of Cd(II) by square wave anode stripping voltammetry (SWASV). At optimal experimental conditions, the observed sensitivity and detection limits of CeFe2O5/GCE are 31.68 mu A/mu M and 0.94 nM, respectively. Our CeFe2O5/GCE exhibits excellent stability (RSD 3.34%) and analytical precision for Cd(II). The CeFe2O5/GCE can also be used in trace detection of heavy metal ions spiked in environmental samples. The nanocomposites with high electrochemical performance would be of great interest for constructing novel sensing platforms for monitoring heavy metal ions in environment. (C) 2020 Elsevier B.V. All rights reserved.

关键词： Yttria stabilized zirconia  

摘要： Solid oxide cells (SOCs) have important applications as fuel cells and electrolyzers. The application for storage of renewable electricity is also becoming increasingly relevant;however, it is difficult to meet stringent area-specific resistance (ASR) and long-term stability targets needed to achieve required efficiency and cost. Here we show a new SOC that utilizes a very thin Gd-doped ceria (GDC)/yttria-stabilized zirconia (YSZ) bi-layer electrolyte, Ni-YSZ cell support with enhanced porosity, and electrode surface modification using PrO(x)and GDC nanocatalysts to achieve unprecedented low ASR values < 0.1 omega cm(2), fuel cell power density similar to 3 W cm(-2), and electrolysis current density similar to 4 A cm(-2)at 800 degrees C. Besides this exceptionally high performance, fuel cell and electrolysis life tests suggest very promising stability in fuel cell and steam electrolysis modes. Electrochemical impedance spectroscopy analysis done using a novel impedance subtraction method shows how rate-limiting electrode processes are impacted by the new SOC materials and design.

关键词： Porosity  

摘要： A large variety of synthetic methods have been developed for hierarchically porous materials by which the performance of a wide range of applications can be dramatically enhanced. Herein, hierarchically porous micropillar arrays are demonstrated by employing electrochemical etching to silicon micropillars. The approach relies on the steering of current flow through the three-dimensional silicon-electrolyte interface to enable nanopores to grow on the entire surface of the micropillars, simultaneously. The pores grow perpendicular to the surface of the micropillars, whereas the pore diameter and porosity vary depending on the locations of the surfaces. The finite element analysis shows that the spatial variation of the pore diameter and porosity is determined by the distribution of current density. Further, the thickness of the porous layer can be tuned by etching time so that sponge-like porous structures are conveniently obtained by regulating the etching time. In addition to the effect of current density flowing through the etched surfaces, the growth of pores also depends on the crystal orientations of the etched surfaces. The etching results on square micropillar arrays and microgroove arrays show that the growth direction and rate of nanopores inside the microstructure also depend on the exposed crystal planes. The facile characteristics of the fabrication method can serve as an effective route for a wide range of applications of porous materials with enhanced capabilities.

关键词： Electro-Fenton   Electroperoxidation   Trifluralin   Kinetic model   Industrial wastewater   Faradaic yield  

摘要： The aim of this manuscript was to investigate indirectly the kinetics of formation of hydroxyl/hydroperoxyl radicals responsible for the degradation of persistent pollutants by electrochemical peroxidation. Experiments involving iron electrodes with and without H2O2 were initially carried out in a batch reactor at 0.2-0.6 A and 25 degrees C in the absence of any pollutants. Concentrations of Fe2+, H2O2, Fe3+, and H+ were determined experimentally as a function of time, and from them a detailed kinetic model comprising 25 electrolysis, dissociation, flotation and Fenton reactions was established. The tuned parameters were only the Faradaic yields for the reactions on the anode, the rate constant for the forward reaction of water dissociation, and flotation of Fe3+. A set of three kinetic experiments of electroperoxidation of trifluralin performed at 0.2 to 0.6 A and 25 degrees C was correctly described by the already presented subset of reactions, plus two others involving trifluralin and hydroxyl/hydroperoxyl radicals. (C) 2020 Elsevier B.V. All rights reserved.

关键词： Reactive electrochemical membrane   Advanced wastewater treatment   Antibiotics removal   Transformation products   Energy consumption  

摘要： The ozone-reactive electrochemical membrane (O-3-REM) coupled process for tetracycline (TC) removal was developed by coupling ozonation and electrochemical oxidation in a substoichiometric titanium dioxide (Ti4O7) REM reactor. To achieve concurrent and efficient degradation-mineralization, TC was treated by ozonation and electrochemical oxidation over the Ti4O7 REM anode in a sequent manner. TC was nearly completely removed within 20 min, while the total organic carbon (TOC) removal efficiency attained 9.1% in 20 min, and then reached 77.1% in 80 min under optimal conditions of 2 mg/min ozone dosage and 2 mA/cm(2) current density. TC was suspected to be oxidized into some four- and three-ring intermediates within 20 min, some two- and one-ring intermediates within 80 min, and eventually carboxylic acids, CO2 and H2O. The concentrations of NO3-, NO2- and NH4+ increased slightly in the first 20 min and then elevated significantly from 20 to 80 min, indicating an enhanced denitrification rate via electrochemical oxidation. Besides, the bioluminescence inhibition ratio exhibited a slight decrease from 54.5% to 50.6% in the first 20 min and then significantly decreased to 14.5% in 80 min, suggesting an augmented toxicity reduction simultaneously by the coupled technology. Overall, the O-3-REM coupled process demonstrated higher TC degradation and TOC removal efficiencies, enhanced toxicity-reduction capability, and lower energy consumption for TC removal compared to individual O-3 or Ti4O7 REM processes. By comprehensively analyzing the performance, mechanism and energy consumption of TC removal by the O-3-REM coupled process, our research provides insights into the application potential of the coupled process to efficiently eliminate the amount and toxicity of various pharmaceuticals from wastewater.

关键词： MgFe2O4 nanoparticles   Alcohol combustion   Reactive red   Adsorption kinetics   Adsorption isotherm  

摘要： Magnetic MgFe2O4 nanoparticles were prepared successfully via a facile alcohol combustion process and applied to remove the reactive red (RR) from aqueous solution. Characterizations of the as-prepared MgFe2O4 nanoparticles were performed by the scanning electron microscopy (SEM), the transmission electron microscope (TEM), the X-ray diffraction (XRD), the vibrating sample magnetometer (VSM), and the Brunauer-Emmett-Teller (BET) measurement. The adsorption characteristics of RR onto MgFe2O4 nanoparticles at room temperature were investigated. Compared with the pseudo-first-order and intraparticle diffusion model, the pseudo-second-order kinetic model could be applied to evaluate the adsorption performance of RR onto MgFe2O4 nanoparticles in a range of initial concentration of 100-400 mg/L. Based on the values of the correlation coefficients, the equilibrium experimental data related to the adsorption of RR showed that the adsorption performance followed the Langmuir isotherm model with maximum adsorption capacity of 119.07 mg/g. The obtained results implied that the adsorption mechanism of RR onto MgFe2O4 nanoparticles at room temperature was the monolayer adsorption. Magnetic MgFe2O4 nanoparticles were prepared via the facile alcohol combustion process, and the magnetic MgFe2O4 nanoparticles were applied to remove the reactive red (RR) from aqueous solution, the adsorption kinetics and adsorption isothermals of RR onto MgFe2O4 nanoparticles at room temperature were investigated. [GRAPHICS] Highlights. MgFe2O4 nanoparticles were prepared via the facile alcohol combustion process.. The pseudo-second-order kinetics model can explain the adsorption process of RR onto them.. The adsorption isotherm of RR onto them at room temperature conformed to Langmuir model.

关键词： Sodium hydroxide  

摘要： This paper reports the comparison of the electrochemical properties of 3D PLA-graphene electrodes (PLA-G) under different activation conditions and through different processes. In this work, the performance of the electrodes was evaluated after polishing, electrochemical and chemical treatments and a combination of them. The best results were obtained with hydroxide activation using 1.0 mol L-1 NaOH for 30 min of immersion, which promoted the saponification of PLA exposing the graphene nanoribbon structures. The improvement was more evident also after electrochemical activation, which led to a great increase in surface area, defects, electron transfer rate and amount of edge sites. The analytical performance of the proposed PLA-G(NaOH-30-EC) electrode was evaluated in the presence of dopamine (DA) by three electrochemical techniques, presenting a broad linear range, and limits of detection of 3.49, 2.17 and 1.67 mu mol L-1 were obtained by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV), respectively. The separation and quantification of DA in the presence of AA and UA was also reported. The sensor showed good repeatability and reproducibility and was successfully applied to DA determination in synthetic urine and human serum, showing good recovery, from 88.8 to 98.4%. Therefore, the activation methods were essential for the improvement in the 3D PLA-G electrode properties, allowing graphene surface alteration and electrochemical enhancement in the sensing of molecular targets.

关键词： Heterogeneous electro-Fenton   Heterogeneous Fenton   Mineral catalyst   Heterogeneous photoelectro-Fenton   Ponceau SS   Water treatment  

摘要： Modified sodium vermiculite, an iron-rich clay mineral, has been used in novel heterogeneous electro-chemical Fenton-based treatments, so-called electro-Fenton (EF)-vermiculite, UVA photoelectro-Fenton (PEF)-vermiculite and solar photoelectro-Fenton (SPEF)-vermiculite. Tests were made with 130 mL of 0.150 mM Ponceau SS diazo dye in 0.050 M Na2SO4 at pH 3.0, in the presence of 1.0 g L-1 catalyst microparticles. The electrolyses were performed in an undivided cell with a boron-doped diamond anode (BDD) and air-diffusion cathode for H2O2 production, at 33.3 mA cm(-2). Decolorization and mineralization were upgraded in the sequence: EF-vermiculite < PEF-vermiculite < SPEF-vermiculite. The removal of organics occurred by the combined action of center dot OH oxidant formed at the BDD surface and homogeneous and heterogeneous Fenton's reactions, along with the photolysis caused by UVA light or sunlight. The homogeneous Fenton's reaction resulted from iron ions leaching, but the heterogeneous mechanism was prevalent. Comparative treatments by anodic oxidation in the presence of H2O2 and homogeneous EF were less effective than EF-vermiculite. The diazo dye absorbance decays agreed with a pseudo-firstorder kinetics. SPEF-vermiculite was the most powerful process, yielding total decolorization and 84.1% mineralization after 300 and 360 min, respectively. The influence of catalyst concentration, current density and diazo dye content on PEF-vermiculite performance was examined. Oxalic, oxamic, malic, tartronic and acetic acids were detected as final short-linear carboxylic acids. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Oxidation  

摘要： The effect of process parameters on the electrochemical performance of a glutamate (Glu) microbiosensor was studied. Glu is a major excitatory neurochemical that is essential for regulation of several brain functions. Glu dysregulation is associated with several neuropathological conditions such as epilepsy, Parkinson's and Alzheimer's disease. Here, an enzymatic microbiosensor in the form of a ceramic-shank substrate enabled platinum (Pt) microelectrode array (MEA) was employed to investigate the effect of key process parameters such as MEA surface cleaning methods, the effects of GluOx concentration, GluOx loading and size-exclusion layer thicknesses on Glu sensitivity and selectivity towards common interferents. A two-step cleaning procedure demonstrated a 57.4% increase in hydrogen peroxide sensitivity, which is due to 80-fold and 2-fold reductions respectively in the charge transfer resistances of the Pt microelectrode grains and grain boundaries. The microbiosensor demonstrated an excellent combination of sensitivity (530 +/- 34 nA cm(-2)mu M-1), selectivity (841 +/- 54) and long-term stability (2 months). These results provide a detailed account of changes in electrochemical properties and sensitivities of Pt microelectrodes toward peroxide, the rationale for choosing a higher GluOx concentration (0.4 U/mu l) instead of 0.1 U/mu l, which is the most commonly used concentration in the literature and recommendations on the enzyme loading and placement of size-exclusion coatings and their deposition conditions, which significantly affects the biosensor performance. (c) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.