Focused microwaves in electrochemical processes

Paired Electrosynthesis at Interdigitated Microband Electrodes: Exploring Diffusion and Reaction Zones in the Absence of a Supporting Electrolyte

Electrosynthesis traditionally requires dedicated reactor systems and an added electrolyte, although some paired electrosynthesis processes are possible at interdigitated microband electrodes simply immersed in solution and without an intentionally added electrolyte. Here, 1,1'-ferrocenedimethanol oxidation and activated olefin electro-hydrogenation reactions are investigated as model processes at a Pt-Pt interdigitated microband array electrode with 5 μm width and with 5 μm interelectrode gap. Voltammetric responses for electro-hydrogenation are discussed, and product yields are determined in methanol (MeOH) in the presence/absence of an added electrolyte (LiClO4). An isotope effect is observed in CH3OD solvent, leading to olefin monodeuteration linked to a fast EC-type process close to the cathode surface (in the cathode reaction zone) rather than to charge annihilation in the interelectrode zone. A finite element simulation is employed to visualize/discuss reaction zones and to contrast the rate of charge annihilation processes with/without a supporting electrolyte.

Microwave-Induced Processing of Free-Standing 3D Printouts: An Effortless Route to High-Redox Kinetics in Electroanalysis

3D-printable composites have become an attractive option used for the design and manufacture of electrochemical sensors. However, to ensure proper charge-transfer kinetics at the electrode/electrolyte interface, activation is often required, with this step consisting of polymer removal to reveal the conductive nanofiller. In this work, we present a novel effective method for the activation of composites consisting of poly(lactic acid) filled with carbon black (CB-PLA) using microwave radiation. A microwave synthesizer used in chemical laboratories (CEM, Matthews, NC, USA) was used for this purpose, establishing that the appropriate activation time for CB-PLA electrodes is 15 min at 70 °C with a microwave power of 100 W. However, the usefulness of an 80 W kitchen microwave oven is also presented for the first time and discussed as a more sustainable approach to CB-PLA electrode activation. It has been established that 10 min in a kitchen microwave oven is adequate to activate the electrode. The electrochemical properties of the microwave-activated electrodes were determined by electrochemical techniques, and their topography was characterized using scanning electron microscopy (SEM), Raman spectroscopy, and contact-angle measurements. This study confirms that during microwave activation, PLAs decompose to uncover the conductive carbon-black filler. We deliver a proof-of-concept of the utility of kitchen microwave-oven activation of a 3D-printed, free-standing electrochemical cell (FSEC) in paracetamol electroanalysis in aqueous electrolyte solution. We established satisfactory limits of linearity for paracetamol detection using voltammetry, ranging from 1.9 μM to 1 mM, with a detection limit (LOD) of 1.31 μM.

A review of microwave-assisted advanced oxidation processes for wastewater treatment

Microwave (MW) technology has gained increasing interest in wastewater treatment due to its unique properties, such as fast and uniform heating, hot spots effect, and non-thermal effect. MW enhances the production of active radicals (e.g., OH, SO₄^-), which exerts a stronger integrated treatment effect in combination with advanced oxidation processes. Over the years, microwave-assisted advanced oxidation processes (MW-AOPs) have developed rapidly to degrade pollutants as innovative treatment approaches. This paper provides a detailed classification and a comprehensive review of MW-AOPs. The latest applications of MW in different advanced oxidation systems (oxidation systems, catalytic oxidation systems, and photochemical, electrochemical and sonochemical systems) are reviewed. The reaction parameters and performance of MW-AOPs in wastewater treatment are discussed, and the enhancement of pollutant degradation by MW is highlighted. In addition, the operating costs of MW-AOPs are evaluated. Some recommendations on MW-AOPs are made for future research. This review provides meaningful information on the potential development and evolution of MW-AOPs.

Scanning Electrochemical Microscopy of Electrically Heated Wire Substrates

We report a new configuration for enhancing the performance of scanning electrochemical microscopy (SECM) via heating of the substrate electrode. A flattened Pt microwire was employed as the substrate electrode. The substrate was heated by an alternating current (AC), resulting in an increased mass transfer between the wire surface and the bulk solution. The electrochemical response of the Pt wire during heating was investigated by means of cyclic voltammetry (CV). The open circuit potential (OCP) of the wire was recorded over time, while varied heating currents were applied to investigate the time needed for establishing steady-state conditions. Diffusion layer studies were carried out by performing probe approach curves (PACs) for various measuring modes of SECM. Finally, imaging studies of a heated substrate electrode surface, applying feedback, substrate generation/tip collection (SG/TC), and the competition mode of SECM, were performed and compared with room temperature results.

Enhanced catalytic performance of reduced graphene oxide-TiO2 hybrids for efficient water treatment using microwave irradiation

Towards achieving efficient waste water treatment, the degradation of a common water pollutant, Orange G azo dye, was studied using a new hybrid catalyst and microwave irradiation. The fabrication of a hybrid catalyst based on reduced graphene oxide-titania (rGO-TiO2), was first achieved in a single mode microwave cavity by reducing the precursor consisting of graphene oxide (GO) and titania. Catalytic performance was then assessed in both microwave assisted and conventional heat treatment conditions. The hybrid catalyst showed significant improvement under microwave irradiation, with more than 88% dye degradation after 20 minutes of treatment at 120 °C. The microwave effect was found to be more dominant in the early stages of the catalysis - the hybrid catalyst decomposed ∼65% of the dye in just 5 minutes of microwave treatment compared to only 18% degradation obtained during conventional heating. The improved performance with microwaves is mainly attributed to the formation of the hot spots at the surface of the hybrid catalyst which ultimately results in higher degradation rates. The morphological and catalytic properties of the hybrid catalyst are investigated using High Resolution Transmission Electron Microscopy (HRTEM) and UV-Vis Spectroscopy, respectively. Successful reduction of GO to rGO was confirmed using Raman spectroscopy and X-ray diffraction. The outstanding performance of microwave irradiated hybrids offers a viable low energy, low carbon footprint process with a new catalyst for wastewater treatment and for highly polluted wastewater conditions where photocatalysis is deemed not feasible.

Electrochemical incineration of high concentration azo dye wastewater on the in situ activated platinum electrode with sustained microwave radiation

In this study, an in situ microwave activated platinum electrode was developed for the first time to completely incinerate the azo dye simulated wastewater containing methyl orange. The experiments were carried out in a circulating system under atmospheric pressure. Azo bond of methyl orange was partly broken on Pt, certain decoloration was reached, and the total organic carbon was not removed effectively without microwave activation. However, methyl orange was mineralized completely and efficiently on the in situ microwave activated Pt. 2,5-Dinitrophenol, p-nitrophenol, hydroquinone, benzoquinone, maleic and oxalic acids are the main intermediates during degradation of methyl orange. Aromatic products are the main substances leading to the poisoning of Pt and decrease of electrochemical oxidation efficiency, so methyl orange removal can not be carried out thoroughly. However, the intermediates were broke down quickly with in situ microwave activation promoting the mineralization of methyl orange on Pt.

Microwave activated electrochemical degradation of 2,4-dichlorophenoxyacetic acid at boron-doped diamond electrode

A method for improving the oxidation ability of the electrode is proposed by using microwave activation in electrochemical oxidation. The electrochemical degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) with microwave radiation (MW-EC) was carried out in a continuous flow system under atmospheric pressure. In 3 h the removal of COD, ACE (average current efficiency) and Cl(-) concentration was 1.63, 2.25 and 1.67 times as that without microwave radiation, respectively. The high degradation ability was resulted from the more active centers at the electrode surface due to the microwave radiation. The decay kinetics of 2,4-D followed a pseudo first-order reaction. The rate constant was increased to 2.16x10(-4) s(-1) with the microwave radiation, while it was 8.52x10(-5) s(-1) with electrochemical treatment only (EC). Under both conditions, the main intermediates were identified and quantified by High Performance Liquid Chromatography (HPLC). The formation rate of intermediate products and further degradation rate were increased by about 50-120% with the microwave radiation. The activation of electrochemical oxidation by microwave was discussed from the diffusion process, adsorption and the temperature at boron-doped diamond (BDD) electrode.

Microwave Induced Jet Boiling Investigated via Voltammetry at Ring−Disk Microelectrodes

High intensity microwave radiation is (self-)focused at metal electrodes immersed in aqueous electrolyte solutions to generate highly localized superheating and convection effects. It is shown that, for an electrode pointing downward, low intensity microwave radiation causes density driven convective flow (upward), which at the onset of boiling abruptly switches to a fast jet of liquid moving away from the electrode surface (downward). This "jet-boiling" phenomenon allows extremely high rates of mass transport and mixing to be realized at the electrode surface. Cyclic voltammograms obtained at electrodes placed into a microwave field show very strong mass transport enhancement effects. Cyclic voltammograms recorded at a Pt/Pt ring-disk electrode system (r(1) = 25 microm, r(2) = 32 microm, r(3) = 32.4 microm) in the presence of microwave radiation are employed to further explore mass transport effects under microwave conditions. Mass transport coefficients, collection efficiencies, and temperatures are determined as a function of microwave intensity.

Capillary electrophoresis with microwave-enhanced electrochemical detection

A new experimental development concerning microwave-assisted electrochemical detection in conjunction with capillary electrophoresis is presented. Focused microwaves are readily incorporated into end-column detection systems for capillary electrophoresis, they induce strong localised thermal activation at microelectrodes, and they affect and modulate, in particular, signals for chemically irreversible redox processes.