Carbon materials syntheses using dielectric barrier discharge microplasma in supercritical carbon dioxide environments

Splitting CO2 in Intense Pulsed Plasma Jets

The splitting of CO₂ was studied in a pulsed plasma discharge produced in a coaxial gun at voltages between ~1 and 2 kV and peak discharge currents of 7 to 14 kA. The plasma was ejected from the gun at a speed of a few km/s and had electron temperatures between 11 and 14 eV with peak electron densities ~2.4 × 10²¹ particles m^-3. Spectroscopic measurements were carried out in the plasma plume produced at pressures between 1 and 5 Torr, and evidence of CO₂ dissociation into oxygen and CO was found. An increased discharge current led to the observation of more intense spectra lines and the presence of new oxygen lines, which implies more dissociation channels. Several dissociation mechanisms are discussed, the main candidate being the splitting of the molecule by direct electron impact. Estimates of dissociation rates are made based on measured plasma parameters and interaction cross-sections available in the literature. A possible application of this technique is in future Mars missions where the coaxial plasma gun running in the atmosphere could be able to produce oxygen at a rate of the order of over 100 g per hour in a highly repetitive regime.

Carbon Dioxide Conversion Synergistically Activated by Dielectric Barrier Discharge Plasma and the CsPbBr3@TiO2 Photocatalyst

Carbon dioxide utilization activated by the integration of plasma and photocatalyst is a promising approach to achieve the mitigation of the greenhouse effect. In this paper, for the first time, the dielectric barrier discharge (DBD) plasma and halide perovskite photocatalysts were synergistically used to facilitate the carbon dioxide conversion. After introducing the photocatalyst into the plasma reactor, the plasma discharge characteristics were improved by the photocatalyst while the active photons, electrons, and vibrationally excited molecules in plasma also enhanced the photocatalytic activity of the photocatalyst. Compared with pure CsPbBr₃ and Al₂O₃, the CsPbBr₃@TiO₂ with the best photocatalytic activity also exhibited the best performance in plasma. The carbon dioxide conversion rate of the DBD plasma filled with CsPbBr₃@TiO₂ was found to be 29.6% higher than the sum of sole plasma and photocatalysis, illustrating the achievement of the synergistic effect between the plasma and photocatalyst. This work brings up new opportunities for efficient large-scale conversion and utilization of carbon dioxide by the coupling of nonthermal plasma and photocatalysis.

Crystalline-to-Amorphous Phase Transformation in CuO Nanowires for Gaseous Ionization and Sensing Application

We report a dramatic reduction of operation voltage of a CuO nanowire-based ionization gas sensor due to the crystalline-to-amorphous phase transformation. The structural change is attributed to the ion bombardment and heating effect during the initial discharge, which brings about the formation of abundant nanocrystallites and surface states favoring gaseous ionization. The gas-sensing properties of the CuO nanowire sensor are confirmed by differentiating various types or concentrations of volatile organic compounds diluted in nitrogen, with a low detection limit at the ppm level. Moreover, a sensing mechanism is proposed on the basis of charge redistribution by electron-gas collision related to the specific ionization energy. The insightful study of the electrode microstructure delivers an exploratory investigation to the effect of gas ionization toward the discharge system, which provides new approaches to develop advanced ionization gas sensors.

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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Nitrogen-Doped Carbon Fiber Paper by Active Screen Plasma Nitriding and Its Microwave Heating Properties

In this paper, active screen plasma nitriding (ASPN) treatment was performed on polyacrylonitrile carbon fiber papers. Electric resistivity and microwave loss factor of carbon fiber were described to establish the relationship between processing parameters and fiber's ability to absorb microwaves. The surface processing effect of carbon fiber could be characterized by dynamic thermal mechanical analyzer testing on composites made of carbon fiber. When the process temperature was at 175 °C, it was conducive to obtaining good performance of dynamical mechanical properties. The treatment provided a way to change microwave heating properties of carbon fiber paper by performing different treatment conditions, such as temperature and time parameters. Atomic force microscope, scanning electron microscope, and X-ray photoelectron spectroscopy analysis showed that, during the course of ASPN treatment on carbon fiber paper, nitrogen group was introduced and silicon group was removed. The treatment of nitrogen-doped carbon fiber paper represented an alternative promising candidate for microwave curing materials used in repairing and heating technology, furthermore, an efficient dielectric layer material for radar-absorbing structure composite in metamaterial technology.

Gas-liquid interfacial plasmas producing reactive species for cell membrane permeabilization

Gas-liquid interfacial atmospheric-pressure plasma jets (GLI-APPJ) are used medically for plasma-induced cell-membrane permeabilization. In an attempt to identify the dominant factors induced by GLI-APPJ responsible for enhancing cell-membrane permeability, the concentration and distribution of plasma-produced reactive species in the gas and liquid phase regions are measured. These reactive species are classified in terms of their life-span: long-lived (e.g., H₂O₂), short-lived (e.g., O₂^•−), and extremely-short-lived (e.g., ^•OH). The concentration of plasma-produced ^•OH_aq in the liquid phase region decreases with an increase in solution thickness (<1 mm), and plasma-induced cell-membrane permeabilization is found to decay markedly as the thickness of the solution increases. Furthermore, the horizontally center-localized distribution of ^•OH_aq, resulting from the center-peaked distribution of ^•OH in the gas phase region, corresponds with the distribution of the permeabilized cells upon APPJ irradiation, whereas the overall plasma-produced oxidizing species such as H₂O_2aq in solution exhibit a doughnut-shaped horizontal distribution. These results suggest that ^•OH_aq is likely one of the dominant factors responsible for plasma-induced cell-membrane permeabilization.

Formation of Graphene Oxide Nanocomposites from Carbon Dioxide Using Ammonia Borane

To efficiently recycle CO(2) to economically viable products such as liquid fuels and carbon nanomaterials, the reactivity of CO(2) is required to be fully understood. We have investigated the reaction of CO(2) with ammonia borane (AB), both molecules being able to function as either an acid or a base, to obtain more insights into the amphoteric activity of CO(2). In the present work, we demonstrate that CO(2) can be converted to graphene oxide (GO) using AB at moderate conditions. The conversion consists of two consecutive steps: CO(2) fixation (CO(2) pressure < 3 MPa and temperature < 100 °C) and graphenization (600-750 °C under 0.1 MPa of N(2)). The first step generates a solid compound that contains methoxy (OCH(3)), formate (HCOO) and aliphatic groups while the second graphenization is the pyrolysis of the solid compound to produce graphene oxide-boron oxide nanocomposites, which have been confirmed by micro-Raman spectroscopy, solid state (13)C and (11)B magic angle spinning-nuclear magnetic resonance (MAS-NMR), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Our observations also show that the mass of solid product in CO(2) fixation process and raw graphene oxide nanocomposites is twice and 1.2 times that of AB initially charged, respectively. The formation of aliphatic groups without using metal-containing compounds at mild conditions is of great interest to the synthesis of various organic products starting from CO(2.).