Discharges In Aqueous Solutions Research Articles

Obtaining Tungsten, Titanium, and Molybdenum Powders during their Dispersion in Pulsed Discharges in Aqueous Solutions

Obtaining Tungsten, Titanium, and Molybdenum Powders during their Dispersion in Pulsed Discharges in Aqueous Solutions

Insight on Solution Plasma in Aqueous Solution and Their Application in Modification of Chitin and Chitosan.

Sustainability and environmental concerns have persuaded researchers to explore renewable materials, such as nature-derived polysaccharides, and add value by changing chemical structures with the aim to possess specific properties, like biological properties. Meanwhile, finding methods and strategies that can lower hazardous chemicals, simplify production steps, reduce time consumption, and acquire high-purified products is an important task that requires attention. To break through these issues, electrical discharging in aqueous solutions at atmospheric pressure and room temperature, referred to as the “solution plasma process”, has been introduced as a novel process for modification of nature-derived polysaccharides like chitin and chitosan. This review reveals insight into the electrical discharge in aqueous solutions and scientific progress on their application in a modification of chitin and chitosan, including degradation and deacetylation. The influencing parameters in the plasma process are intensively explained in order to provide a guideline for the modification of not only chitin and chitosan but also other nature-derived polysaccharides, aiming to address economic aspects and environmental concerns.

Chemical transformations initiated by gas discharges in aqueous solutions

The kinetic regularities of the processes of oxidation-reduction of chromium ions under the action of a direct current discharge of atmospheric pressure in air, oxygen and argon on an aqueous solution of potassium dichromate at currents of 20–60 mA and concentrations 0.092–0.4 mmol·l−1 are investigated. The solution served as the cathode of the discharge. It was found that the effect of a discharge in any gas on a solution stimulates the reversible Cr6+↔Cr3+ reactions of oxidation-reduction of chromium ions. The apparent constants of the rates of oxidation and reduction and their dependence on the discharge current and initial concentration are found. The energy efficiency of the process is estimated. It is shown that the discharge in argon is most effective for carrying out the reduction process.

OXIDATIVE-REDUCING PROCESSES WITH PARTICIPATION OF MANGANESE IONS INITIATED BY AN ELECTRIC DISCHARGE IN AQUEOUS SOLUTION

The results of experimental studies of the kinetics of oxidation-reduction of Mn7+ ions (MnO4-) in aqueous solutions initiated by the action of a discharge of a direct current of atmospheric pressure in air are analyzed in the article. A solution of potassium permanganate served as a discharge cathode. The range of initial solution concentrations for Mn7+ ions was (0.44-2.5) mmol/l, and discharge currents (20-60) mA. It was found that the discharge action leads to the reduction of Mn7+ ions and discoloration of the solution. At the same time, dark solid particles with a size of 0.1 μm to 20 μm are formed. X-ray diffraction analysis showed that the particles are amorphous, and energy dispersive X-ray analysis showed that the powder is manganese oxide (IV). The kinetics of reduction-oxidation of Mn7+ ions is measured. It is shown that the obtained data on the kinetics of the reduction of Mn7+ ions in the best way (the determination coefficient R2≈0.99) can be described by the scheme X↔Y↔Z, where X is the starting material, and Y and Z are the reaction products. The processing of kinetic curves on the basis of this scheme found the effective rate constants of the corresponding stages. It was found that the effective rate constants depend on the initial concentration of the solution. At a discharge current of 20 mA, an increase in the concentration from 0.44 to 2.5 mol/l led to a decrease in the rate constant for the reduction of Mn7+ ions from (2.48 ± 0.5) ·10-2 to (7.2 ± 1.5) ·10-3 s-1, respectively. Possible mechanisms of processes are discussed. It is assumed that the main particles involved in the oxidation reactions of the reduction of manganese ions are H2O2, HO2, OH and solvated electrons that are formed in the solution under the action of a discharge.
 For citation:
 Shutov D.A., Sungurova A.V., Smirnova K.V., Manukyan A.S., Rybkin V.V. Oxidative-reducing processes with participation of manganese ions initiated by electric discharge in aqueous solution. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 9-10. P. 23-29

Air-supplied pinhole discharge in aqueous solution for the inactivation of Escherichia coli

An air-supplied pinhole discharge in aqueous solution has been developed to provide a short-lived and odorless bactericide to replace current conventional disinfectants such as O3, ClO−, HClO, and ClO2. The pinhole discharge that was initiated inside a water bubble generated hydrogen peroxide (H2O2) and nitrous acid (HNO2) simultaneously. The concentrations of H2O2, HNO2, and HNO3 were 16.3, 13.9, and 17.4 mg/L, respectively when flow rates of NaCl solution and air were 72 and 12.5 mL/min, respectively. The pH value of the solution was 3.87, and HO2 radicals were generated from the reaction of H2O2 with HNO2. The efficacy of sterilization of discharge-treated water was evaluated by changing the acetic solutions. A 4-orders-of-magnitude decrease in Escherichia coli survival rate was observed after treatment with a sodium citrate solution of pH 3.2 for 60 s.

Aqueous Plasma Pharmacy: Preparation Methods, Chemistry, and Therapeutic Applications.

Plasma pharmacy is a subset of the broader field of plasma medicine. Although not strictly defined, the term aqueous plasma pharmacy (APP) is used to refer to the generation and distribution of reactive plasma-generated species in an aqueous solution followed by subsequent administration for therapeutic benefits. APP attempts to harness the therapeutic effects of plasma-generated oxidant species within aqueous solution in various applications, such as disinfectant solutions, cell proliferation related to wound healing, and cancer treatment. The subsequent use of plasma-generated solutions in the APP approach facilitates the delivery of reactive plasma species to internal locations within the body. Although significant efforts in the field of plasma medicine have concentrated on employing direct plasma plume exposure to cells or tissues, here we focus specifically on plasma discharge in aqueous solution to render the solution biologically active for subsequent application. Methods of plasma discharge in solution are reviewed, along with aqueous plasma chemistry and the applications for APP. The future of the field also is discussed regarding necessary research efforts that will enable commercialization for clinical deployment.

Facile synthesis of Pt–Pd bimetallic nanoparticles by plasma discharge in liquid and their electrocatalytic activity toward methanol oxidation in alkaline media

The Pt–Pd bimetallic nanoparticles for direct methanol fuel cell applications were successfully prepared by plasma discharge in aqueous solution. The obtained nanoparticles were characterized by energy dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, and transmission electron microscopy. During plasma discharge, the nanoparticles were produced from the erosion of electrodes. It was noted that the erosion amount of anode electrodes was much greater than that of cathode electrodes so that the composition of Pt–Pd bimetallic nanoparticles could be changed with different power types and electrode configurations. Diffraction patterns fitted from Gaussian devolution indicated that the crystalline phase of Pt40Pd60 products was composed of pure Pt, pure Pd and Pt–Pd alloy phases. The morphology of synthesized nanoparticles showed that nanowires connected with quasi-spherical nanoparticles with 2–3nm in diameter were observed and large spherical particles with >50nm in diameter were also detected intermittently. The cyclic voltammetric measurement and continuous potential scan demonstrated that Pt40Pd60 had much higher catalytic activity and better resistance to CO poisoning than Pt94Pd6 and Pt1Pd99 for methanol oxidation. These results indicate that the Pt40Pd60 could be an excellent candidate for the direct methanol fuel cell applications.

Synthesis Process of Cobalt Nanoparticles in Liquid-Phase Plasma

In this work, the liquid phase plasma reduction method was applied to prepare cobalt nanoparticles from the cobalt chloride solution. A bipolar pulsed power supply was used to generate discharges in aqueous solutions. The excited states of atomic hydrogen and atomic oxygen as well as the molecular bands of the hydroxyl radical OH were detected in emission spectra. The duration of plasma treatment affected not only size and number of produced particles but also the particle shape. Many spots could be seen in the Electron diffraction pattern of polycrystalline particles.

Formation of Active Species by Bipolar Pulsed Discharge in Water

Water treatment by the direct electrical discharge in aqueous solution is an innovative advanced oxidation technology of water treatment. During the discharge processes, a large amount of high-energy electrons and active species, such as H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , are produced. Those active species directly react with organic molecules dissolved in water and oxidize them or even get them completely mineralized. In this paper, the concentrations of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> in a gas-liquid-solid mixture treated by bipolar pulsed discharges were measured. The effect of different experiment conditions on the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> concentration was investigated. Experimental results prove that bipolar pulsed discharges in a packed bed reactor have a better performance on H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> generation than unipolar pulsed discharges. Besides, parameters, such as the discharge time, the applied voltage, the characteristics of the solid packing, and the gas flow rate, were positively correlated with the generation of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> . Essentially, the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> concentrations were mainly influenced by the single pulse energy that was also verified by experiments.

FORMATION OF CARBON NANOTUBES IN IRON-CATALYZED LIQUID ARCING METHOD: EFFECT OF IRON-ION CHARGE IN THE AQUEOUS MEDIUM

Carbon nanotubes (CNTs) were synthesized via arc discharge in aqueous solutions containing ferrous and ferric irons to reveal the effect of iron-charge mole ratio, R = [ Fe 2+]/[ Fe 3+], on the purity of CNTs and the process yield. Raman spectroscopy and transmission electron microscopy were used to analyze the cathodic deposits. It is shown that the nucleation of multi-walled CNTs is catalyzed by ferric irons while their growth is affected by ferrous ions. Well-graphitized CNTs with a high-yield are obtained at R = 1 and total iron concentration of 0.05 M. The effect of iron charge is described based on the two-stage formation mechanism.

The electrochemical discharges for the synthesis of nickel oxide nanoparticles: Characterization and mechanism

Electrochemical discharges in aqueous solution of sulphuric acid and ethanol as scavenger of hydroxyl radicals, in addition to polyvinylpyrrolidone as stabilizing agent are used for the synthesis of nano-sized nickel oxide colloids. Morphological characterization by electron microscopy and powder X-ray diffraction has been performed to examine the obtained particles at different terminal voltages and experiment durations. From the qualitative resemblance of the electrochemical discharges to the radiolysis technique, a microscopic mechanistic model is proposed giving an overall picture of the physicochemical phenomenon for the synthesis of fine particles.

Solution Plasma Process for Template Removal in Mesoporous Silica Synthesis

The plasma discharge in aqueous solution was scientifically studied and applied to template removal in mesoporous silica synthesis. Highly dispersed spherical mesoporous silica particles were synthesized by the ternary surfactant system containing the Pluronic P123 copolymer (EO20PO69EO20), sodium dodecylbenzene sulfonate, and 1,1,2,2,3,3,4,4,4-nonafluoro-1-butane sulfonate, via the sol–gel method in acid solutions. The solution plasma process (SPP), instead of conventional thermal calcinations, was used to remove the template. The mechanism of the removal of the organic template occurred via oxidation by the hydroxyl radicals generated during discharge. The transformation of a mesopore structure from a disordered wormlike structure to a hexagonally arranged structure was observed by X-ray diffraction analysis and was confirmed by transmission electron microscopy. The results of the thermal analysis and functional group identification of mesoporous silica after SPP showed evidence of organic template removal. The surface area calculated using the Brunauer–Emmett–Teller (BET) theory and the mean pore diameter results could be used to evaluate the plasma efficiency, demonstrating that this method does not affect the pore size in the case of discharge in a solution of pH 3 compared with the results of thermal calcination. Hence, SPP was proved to be highly efficient for organic template removal, exhibiting short consumption time and less contamination.

Effect of Fe 3+ concentration on MWCNTs formation in liquid arcing method

The formation of multi-walled carbon nanotubes (MWCNTs) during arc discharge in aqueous solutions of Fe 2(SO 4) 3 and FeCl 3 was studied. The concentration of iron ions changed from zero (deionized water) to 0.25 M and the cathodic products were examined by transmission electron microscopy, Raman spectrometry, and thermal gravimetric analysis. The experimental results showed that the crystallinity of MWCNTs is improved by increasing the concentration of iron ions. Nevertheless, the process yield and overall quality of the produced CNTs were significantly affected by iron concentration in the aqueous solution. This observation suggested that there should be an optimum iron concentration at which the formation of MWCNTs is favored. As compared with the sulfate solution, a higher process yield is obtained in the presence of chloride ions in agreement with previous reports.

Continuous synthesis of colloidal silver nanoparticles by electrochemical discharge in aqueous solutions

This article presents an electrochemical discharge (ECD) method that consists of a combination of chemical methods and electric arc discharges. In the method, 140 V is applied to an Ag electrode from a DC power supply. The arc-discharge between the electrodes produces metallic silver nanoparticles and silver ions in the aqueous solution. Compared with the original arc discharge, this ECD method creates smaller nanoparticles, prevents clumping of the nanoparticles, and shortens the production time. The citrate ions also reduce the silver ions to silver nanoparticles. In addition, the citrate ions cap the surface of the produced silver nanoparticles and the zeta potential increases. In this article, the weight loss of the electrodes and the reduction of silver ions to silver nanoparticles as a function of citrate concentration and electric conductivity of the medium are discussed. Furthermore, the properties of the colloidal silver prepared with ECD are analyzed by UV–Vis spectroscopy, dynamic light scattering, electrophoresis light scattering, and scanning electron microscopy. Finally, a continuous production apparatus is presented for the continuous production of colloidal silver.

(Invited) Microscale Plasma Discharges in Aqueous Solutions: New Technique for Localized Synthesis of Nanoparticles

not Available.

Preparation of diamond-like carbon films by cathodic micro-arc discharge in aqueous solutions

Diamond-like carbon films (DLC) and silicon doped diamond-like carbon films were deposited on Ni substrate by cathodic micro-arc discharge at room temperature in aqueous solutions. The deposit potential was 130 V. The structure of the films was characterized by a scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Raman spectra and XPS analysis demonstrated that the films were diamond-like carbon clearly. SEM observation showed that the DLC films were uniform and the thickness was about 200 nm. Potentiodynamic polarization curve indicated the corrosion resistance of the Ni substrate was markedly improved by DLC films.

Localized Synthesis of Metal Nanoparticles Using Nanoscale Corona Discharge in Aqueous Solutions

Highly localized and controlled metal nanoparticle synthesis using nanoscale corona discharge in aqueous solutions is illustrated. As a case study, gold nanoparticles are successfully deposited at the very tip of carbon nanopipettes to act as surface-enhanced Raman spectroscopy (SERS) probes.

Synthesis process of gold nanoparticles in solution plasma

We describe the dynamics of the synthesis of gold nanoparticles by a glow discharge in aqueous solutions. A pulsed power supply was used to generate discharges in the aqueous solutions. The initial [AuCl 4] − ion concentration and the voltage applied between the electrodes were varied. The [AuCl 4] − ion was reduced by the H radicals generated in the discharge. The reduction rates were calculated from the changes in the [AuCl 4] − ion concentration during the discharge time. Dendrite-shaped nanoparticles of about 150 nm size were formed in discharge during 1 min. The pH of the solution decreased gradually with the increase of the discharge time. The decrease in pH led to the dissolution of gold nanoparticles. The reduction and the dissolution rates increased proportionately with the applied voltage. The size of the gold nanoparticles decreased at 20 nm after running the discharge during 45 min. Moreover gold nanoparticles with exotic shapes, such as triangle, pentagon, and hexagon were also observed. The particles were confirmed to be as polycrystalline gold nanoparticles by electron diffraction patterns. In summary, when the reduction rate lowered as a result of dissolution, anisotropic nanoparticles were formed and continued to grow in size in the solution.

Gas film formation time and gas film life time during electrochemical discharge phenomenon

The formation of a gas film around an electrode is at the origin of the electrochemical discharges in aqueous solutions and in molten salts. The study of the electrochemical discharge phenomenon from the current signal point of view is conducted to identify the gas film formations and the following discharges. This is performed using the wavelet analysis as a denoising tool with the discrete Meyer wavelet as base function. The proposed algorithm allows to measure experimentally the gas film life time and its necessary building time prior to each series of discharges. The accuracy of the algorithm is evaluated using generated signals and its application to real data is demonstrated. From the experimental data, it is concluded that the gas film is more stable at high terminal voltages whereas its formation time decreases with it. Electrochemical and thermal interpretations for the measured statistics are proposed.

Exotic shapes of gold nanoparticles synthesized using plasma in aqueous solution

Gold nanoparticles with exotic shapes, such as triangle, pentagon, and hexagon, have been synthesized by glow discharge in aqueous solutions. A pulsed power supply was used to generate discharges in the aqueous solutions. Pulse width and frequency were 2 μs and 15 kHz, respectively. Discharges were generated at applied voltages of 1600 and 3200 V. The shapes of the gold nanoparticles and electron diffraction patterns were observed by transmission electron microscopy. The nanoparticles obtained were about 20 nm in diameter. In particular, at the higher voltage of 3200 V, nanoparticles with anisotropic shapes were synthesized. In the initial stages of synthesis, diameter decreased with discharge time as the nanoparticles redissolved in the solution. After discharge for 25 min, nanoparticles with anisotropic shapes appeared. This discharge led to the generation of H2O2 and a decrease in pH as a result of the consumption of OH radicals during the generation of H2O2 and electron donation of H radicals to the solution. After the pH stopped decreasing, H radicals mainly reacted as a reducing agent. The decrease in pH allowed redissolution of the gold nanoparticles. The gold dust particles that were not completely dissolved acted as new seeds for nucleation. Thus, the two reaction steps, nucleation and nuclear growth, occur during the formation of gold nanoparticles with exotic shapes.