Employing Plasmas as Gaseous Electrodes at the Free Surface of Ionic Liquids: Deposition of Nanocrystalline Silver Particles

Probing time-resolved plasma-driven solution electrochemistry in a falling liquid film plasma reactor: Identification of HO2- as a plasma-derived reducing agent

Many applications involving plasma-liquid interactions depend on the reactive processes occurring at the plasma-liquid interface. We report on a falling liquid film plasma reactor allowing for in situ optical absorption measurements of the time-dependence of the ferricyanide/ferrocyanide redox reactivity, complemented with ex situ measurement of the decomposition of formate. We found excellent agreement between the measured decomposition percentages and the diffusion-limited decomposition of formate by interfacial plasma-enabled reactions, except at high pH in thin liquid films, indicating the involvement of previously unexplored plasma-induced liquid phase chemistry enabled by long-lived reactive species. We also determined that high pH facilitates a reduction-favoring environment in ferricyanide/ferrocyanide redox solutions. In situ conversion measurements of a 1:1 ferricyanide/ferrocyanide redox mixture exceed the measured ex situ conversion and show that conversion of a 1:1 ferricyanide/ferrocyanide mixture is strongly dependent on film thickness. We identified three dominant processes: reduction faster than ms time scales for film thicknesses >100 µm, •OH-driven oxidation on time scales of <10 ms, and reduction on 15 ms time scales for film thickness <100 µm. We attribute the slow reduction and larger formate decomposition at high pH to HO2- formed from plasma-produced H2O2 enabled by the high pH at the plasma-liquid interface as confirmed experimentally and by computed reaction rates of HO2- with ferricyanide. Overall, this work demonstrates the utility of liquid film reactors in enabling the discovery of new plasma-interfacial chemistry and the utility of atmospheric plasmas for electrodeless electrochemistry.

Ionic Liquids and Deep Eutectics as a Transformative Platform for the Synthesis of Nanomaterials

Ionic liquids (ILs) are becoming a revolutionary synthesis medium for inorganic nanomaterials, permitting more efficient, safer and environmentally benign preparation of high quality products. A smart combination of ILs and...

Aqueous Gold Nanoparticles Generated by AC and Pulse-Power-Driven Plasma Jet

In this study, we developed a simple-to-use approach based on an atmospheric pressure plasma jet to synthesize aqueous Au nanoparticles (AuNP). Special attention was paid to the different reaction dynamics and AuNP properties under AC and pulse-power-driven plasma jets (A-Jet and P-Jet, respectively). The morphology of the AuNP, optical emissions, and chemical reactions were analyzed. Further, a copper mesh was placed above the reaction cell to evaluate the role of electrons and neutral species reduction. A visible color change was observed after the A-Jet treatment for 30 s, while it took 3 min for the P-Jet. The A-Jet treatment presented a much higher AuNP growth rate and a smaller AuNP diameter compared with the P-Jet treatment. Further analysis revealed an increase in chemical concentrations (Cl⁻ and H₂O₂) and liquid conductivity after plasma treatment, with a higher increased amplitude for the A-Jet case. Moreover, the electrons alone had little effect on AuNP generation, while neutral species showed a clear Au⁺ reduction effect, and a unique coupling effect between both reactions was observed. The different reaction dynamics between the A-Jet and P-Jet were attributed to their different local heating effects and different discharge power during the reaction.

Applications of Plasma-Liquid Systems: A Review

Plasma-liquid systems have attracted increasing attention in recent years, owing to their high potential in material processing and nanoscience, environmental remediation, sterilization, biomedicine, and food applications. Due to the multidisciplinary character of this scientific field and due to its broad range of established and promising applications, an updated overview is required, addressing the various applications of plasma-liquid systems till now. In the present review, after a brief historical introduction on this important research field, the authors aimed to bring together a wide range of applications of plasma-liquid systems, including nanomaterial processing, water analytical chemistry, water purification, plasma sterilization, plasma medicine, food preservation and agricultural processing, power transformers for high voltage switching, and polymer solution treatment. Although the general understanding of plasma-liquid interactions and their applications has grown significantly in recent decades, it is aimed here to give an updated overview on the possible applications of plasma-liquid systems. This review can be used as a guide for researchers from different fields to gain insight in the history and state-of-the-art of plasma-liquid interactions and to obtain an overview on the acquired knowledge in this field up to now.

Synthesis of metallic nanoparticles by microplasma

The synthesis of metallic nanoparticles has been of long standing interest, primarily induced by their novel and unique properties that differ considerably from bulk materials. Despite various methods have been developed, it is still a challenge to produce high-quality metallic nanoparticles with controllable properties in a simple, cost-effective and environmentally benign manner. However, the development of the microplasma-assisted technology can bring an answer to this formidable challenge. In the present work, four main microplasma configurations used for metallic synthesis of metallic nanoparticles are reviewed.  These are  hollow-electrode microdischarges, microplasma jets with external electrodes, microplasma jets with consumable electrodes and plasma–liquid systems. The state of the art characterization methodologies and diagnostic techniques for in situ microplasma-assisted precursor dissociation as well as ex situ metallic nanoparticles analysis is also summarized. Further, a broad category of representative examples of microplasma-induced metallic nanoparticle fabrication is presented, together with the discussion of possible synthesis mechanisms. This is followed by a brief introduction to related safety considerations. Finally, the future perspectives, associated challenges and feasible solutions for scale-up of this technique are pointed out.

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In-liquid plasma: a novel tool in the fabrication of nanomaterials and in the treatment of wastewaters

Attempts to generate plasma in liquids have been successful and various devices have been proposed.

Mesoporous Face-Centered-Cubic In4Ni Alloy Nanorices: Superior Catalysts for Hydrazine Dehydrogenation in Aqueous Solution

Mesoporous face-centered-cubic (fcc) In4Ni alloy nanorices (NRs) were successfully synthesized as superior catalysts for N2H4 dehydrogenation in aqueous solution via a facile solution plasma technique (SPT) in an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). This incorporation introduces basic sites for dehydrogenation. Also, the synthesis of In and Ni weakens the interactions among generated adspecies such as H2 and NHx and surface metal atoms. Alongside their unique NR structure, the as-prepared fcc-In4Ni alloy NRs exhibited superior performance for N2H4 dehydrogenation in aqueous solution. The activation energy of the fcc-In4Ni alloy NRs was 38.9 ± 1.0 kJ mol(-1). The NRs were also found to be stable for catalytic N2H4 dehydrogenation in aqueous solution, providing an average TOF value of 82.0 (mol of H2 (mol of active In4Ni min)(-1)) over 30 h reaction. These fcc-In4Ni alloy NRs have demonstrated exceptional performance, which indicates that the construction of hydrogen-producing systems from N2H4, capable of matching the performance of NaBH4 and NH3BH3 hydrogen-producing systems for fuel-cell applications, is a promising possibility.

Influence of reactive oxygen species on the enzyme stability and activity in the presence of ionic liquids

In this paper, we have examined the effect of ammonium and imidazolium based ionic liquids (ILs) on the stability and activity of proteolytic enzyme α-chymotrypsin (CT) in the presence of cold atmospheric pressure plasma jet (APPJ). The present work aims to illustrate the state of art implementing the combined action of ILs and APPJ on the enzyme stability and activity. Our circular dichroism (CD), fluorescence and enzyme activity results of CT have revealed that buffer and all studied ILs {triethylammonium hydrogen sulphate (TEAS) from ammonium family and 1-butyl-3-methyl imidazolium chloride ([Bmim][Cl]), 1-methylimidazolium chloride ([Mim][Cl]) from imidazolium family} are notable to act as protective agents against the deleterious action of the APPJ, except triethylammonium dihydrogen phosphate (TEAP) ammonium IL. However, TEAP attenuates strongly the deleterious action of reactive oxygen species (ROS) created by APPJ on native structure of CT. Further, TEAP is able to retain the enzymatic activity after APPJ exposure which is absent in all the other systems.This study provides the first combined effect of APPJ and ILs on biomolecules that may generate many theoretical and experimental opportunities. Through this methodology, we can utilise both enzyme and plasma simultaneously without affecting the enzyme structure and activity on the material surface; which can prove to be applicable in various fields.

Plasma electrochemistry: development of a reference electrode material for high temperature plasma

This report describes the development of a high temperature reference electrode material for gas phase electrochemistry investigations. The electrode is constructed by careful assessment of different metal/metal oxide materials and operational stability in flame electrolyte medium. This will enable reliable dynamic electrochemistry investigations into redox reactions at the solid/gas interface, free of any solvent defined potential window restrictions.

Reduction and removal of aqueous Cr(VI) by glow discharge plasma at the gas-solution interface

Aqueous chromium(VI) reduction and removal induced by glow discharge taking place at the gas-solution interface in an argon atmosphere was studied. The effect of initial pH and hydroxyl radical scavenger (ethanol) on the reduction efficiency was examined. High reduction efficiency was obtained when initial pH ≤ 2.0 or ≥ 8.0. In particular, addition of ethanol into the solution substantially increased the reduction efficiency and facilitated chromium removal from the solution in the form of sediment after discharge. The optimum pH values for Cr(VI) removal were within 6.0-7.0. Fourier transform-infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analysis confirmed that the main constituent of the sediment is chromium hydroxide.

Growth of sputter-deposited gold nanoparticles in ionic liquids

The growth of gold nanoparticles (NPs) synthesized by sputter deposition on an ionic liquid surface is studied in situ in the bulk phase of the ionic liquids (ILs) 1-butyl-3-methylimidazolium dicyanamide [C(1)C(4)Im][N(CN)(2)], 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [C(1)C(4)Im][Tf(2)N], 1-butyl-3-methylimidazolium tetrafluoroborate [C(1)C(4)Im][BF(4)], 1-butyl-3-methylimidazolium hexafluorophosphate [C(1)C(4)Im][PF(6)] and 1-butyl-3-methylimidazolium triflate [C(1)C(4)Im][TfO]. It is found that primary nanoparticles with a diameter smaller than 2.5 nm are present in the sample immediately after sputtering. Growth of these primary particles proceeds after the end of the sputtering process and stops when the nanoparticles reach a certain size. Depending on the viscosity of the ionic liquid this growth process can proceed several hours to several days. The growth speed is fastest for the least viscous ionic liquid and follows the trend [C(1)C(4)Im][N(CN)(2)] > [C(1)C(4)Im][Tf(2)N] > [C(1)C(4)Im][TfO] > [C(1)C(4)Im][BF(4)] > [C(1)C(4)Im][PF(6)]. It is also found that a higher concentration of sputtered gold results in faster growth of the gold nanoparticles. A discussion on the growth mechanism of sputtered gold NPs is included.

New frontiers in materials science opened by ionic liquids

Ionic liquids (ILs) including ambient-temperature molten salts, which exist in the liquid state even at room temperature, have a long research history. However, their applications were once limited because ILs were considered as highly moisture-sensitive solvents that should be handled in a glove box. After the first synthesis of moisture-stable ILs in 1992, their unique physicochemical properties became known in all scientific fields. ILs are composed solely of ions and exhibit several specific liquid-like properties, e.g., some ILs enable dissolution of insoluble bio-related materials and the use as tailor-made lubricants in industrial applications under extreme physicochemical conditions. Hybridization of ILs and other materials provides quasi-solid materials, which can be used to fabricate highly functional devices. ILs are also used as reaction media for electrochemical and chemical synthesis of nanomaterials. In addition, the negligible vapor pressure of ILs allows the fabrication of electrochemical devices that are operated under ambient conditions, and many liquid-vacuum technologies, such as X-ray photoelectron spectroscopy (XPS) analysis of liquids, electron microscopy of liquids, and sputtering and physical vapor deposition onto liquids. In this article, we review recent studies on ILs that are employed as functional advanced materials, advanced mediums for materials production, and components for preparing highly functional materials.

Synthesis and characterization of nickel nanoparticles dispersed in imidazolium ionic liquids

The diameter and size-distribution of Ni nanoparticles prepared by the decomposition of [bis(1,5-cyclooctadiene)nickel(0)] organometallic precursor dissolved in 1-alkyl-3-methylimidazolium N-bis(trifluoromethanesulfonyl) amide ionic liquids depend on the length of the alkyl side-chain of the imidazolium ring. The increase of the organization range order of the ionic liquid that increases with that of the alkyl side-chain (from n-butyl to n-hexadecyl) induces the formation of nanoparticles with a smaller diameter and size-distribution. The cubic fcc Ni nanoparticles with 4.9 +/- 0.9 to 5.9 +/- 1.4 nm in mean diameter and monomodal size-distribution thus prepared are probably composed of a small cap layer of NiO around a core of Ni metal. The contribution of the oxide layer also depends on the medium i.e. the metal oxide ratio increases in salts containing four to eight carbons on their side-chains and then decreases as the number of carbons increases. The Ni nanoparticles dispersed in the ionic liquids are active catalysts for the hydrogenation of olefins under relatively mild reaction conditions.