Qiang Chen

A review of plasma–liquid interactions for nanomaterial synthesis

Over the past few decades, a new branch of plasma research, nanomaterial (NM) synthesis through plasma–liquid interactions (PLIs), has been developing rapidly, mainly due to the various, recently developed plasma sources operating at low and atmospheric pressures. PLIs provide novel plasma–liquid interfaces where many physical and chemical processes take place. By exploiting these physical and chemical processes, various NMs ranging from noble metal nanoparticles to graphene nanosheets can easily be synthesized. The currently rapid development and increasingly wide utilization of the PLI method has naturally lead to an urgent need for the presentation of a general review. This paper reviews the current status of research on PLIs for NM synthesis. The focus is on a comprehensive understanding of the synthesis process and perceptive opinions on current issues and future challenges in this field.

The characterization of radio-frequency discharge using electrolyte solution as one electrode at atmospheric pressure

Atmospheric pressure discharges driven by radio-frequency source were generated using electrolyte solution as one electrode. The electron density calculated from the Stark broadening of Hβ (486.1u2009nm) was in the order of 1015u2009cm−3 and showed a parabolic shape with the pH value of the solution. The simulated gas temperature increased from 950 to 2750u2009K as the input power increased from 12 to 40u2009W. We found that the plasma exposure was accompanied with the acidification of the solution electrode; it was ascribed to the dissolution of nitrogen-related compounds, such as HNO2, HNO3 and NxOy which originate from the oxidation of nitrogen in air. Also, solute atom line emission was observed in the plasma zone and evaporation was demonstrated to play an important role in the solute transport.

Deposition of controllable preferred orientation silicon films on glass by inductively coupled plasma chemical vapor deposition

An inductively coupled plasma (ICP) system with the adjustable distance between the inductance coil and substrates was designed to effectively utilize the spatial confinement of ICP discharge, and then control the gas-phase transport process. The effects of the gas phase processes on the crystallinity and preferred orientation of silicon films deposited on glass were systematically investigated. The investigation was conducted in the ICP-chemical vapor deposition process with the precursor gas of a SiH4∕H2 mixture at a substrate temperature of 350°C. Highly crystallized silicon films with different preferred orientations, (111) or (220), could be selectively deposited by adjusting the SiH4 dilution ratio [R=[SiH4]∕([SiH4]+[H2])] or total working pressure. When the total working pressure is 20Pa, the crystallinity of the silicon films increases with the increase of the SiH4 dilution ratio, while the preferred orientation was changed from (111) to (220). In the case of the fixed SiH4 dilution (10%), the sil...

Synergistic Effect of Atmospheric-pressure Plasma and TiO2 Photocatalysis on Inactivation of Escherichia coli Cells in Aqueous Media.

Atmospheric-pressure plasma and TiO2 photocatalysis have been widely investigated separately for the management and reduction of microorganisms in aqueous solutions. In this paper, the two methods were combined in order to achieve a more profound understanding of their interactions in disinfection of water contaminated by Escherichia coli. Under water discharges carried out by microplasma jet arrays can result in a rapid inactivation of E. coli cells. The inactivation efficiency is largely dependent on the feed gases used, the plasma treatment time, and the discharge power. Compared to atmospheric-pressure N2, He and air microplasma arrays, O2 microplasma had the highest activity against E. coli cells in aqueous solution, and showed >99.9% bacterial inactivation efficiency within 4u2009min. Addition of TiO2 photocatalytic film to the plasma discharge reactor significantly enhanced the inactivation efficiency of the O2 microplasma system, decreasing the time required to achieve 99.9% killing of E. coli cells to 1u2009min. This may be attributed to the enhancement of ROS generation due to high catalytic activity and stability of the TiO2 photocatalyst in the combined plasma-TiO2 systems. Present work demonstrated the synergistic effect of the two agents, which can be correlated in order to maximize treatment efficiency.

Effect of rGO Coating on Interconnected Co3O4 Nanosheets and Improved Supercapacitive Behavior of Co3O4/rGO/NF Architecture

AbstractIn this study, the effect of reduced graphene oxide (rGO) on interconnected Co3O4 nanosheets and the improved supercapacitive behaviors is reported. By optimizing the experimental parameters, we achieved a specific capacitance of ~1016.4xa0Fxa0g−1 for the Co3O4/rGO/NF (nickel foam) system at a current density of 1xa0Axa0g−1. However, the Co3O4/NF structure without rGO only delivers a specific capacitance of ~520.0 Fxa0g−1 at the same current density. The stability test demonstrates that Co3O4/rGO/NF retains ~95.5% of the initial capacitance value even after 3000 charge–discharge cycles at a high current density of 7xa0Axa0g−1. Further investigation reveals that capacitance improvement for the Co3O4/rGO/NF structure is mainly because of a higher specific surface area (~87.8xa0m2xa0g−1) and a more optimal mesoporous size (4–15xa0nm) compared to the corresponding values of 67.1xa0m2xa0g−1 and 6–25xa0nm, respectively, for the Co3O4/NF structure. rGO and the thinner Co3O4 nanosheets benefit from the strain relaxation during the charge and discharge processes, improving the cycling stability of Co3O4/rGO/NF.n

Direct synthesis of hydrogen peroxide from plasma-water interactions

Hydrogen peroxide (H2O2) is usually considered to be an important reagent in green chemistry since water is the only by-product in H2O2 involved oxidation reactions. Early studies show that direct synthesis of H2O2 by plasma-water interactions is possible, while the factors affecting the H2O2 production in this method remain unclear. Herein, we present a study on the H2O2 synthesis by atmospheric pressure plasma-water interactions. The results indicate that the most important factors for the H2O2 production are the processes taking place at the plasma-water interface, including sputtering, electric field induced hydrated ion emission, and evaporation. The H2O2 production rate reaches ~1200u2009μmol/h when the liquid cathode is purified water or an aqueous solution of NaCl with an initial conductivity of 10500u2009μS cm−1.

Nanostructured semiconductor solar absorbers with near 100% absorption and related light management picture

Optical behaviors of both polycrystalline silicon (Si) and gallium arsenide (GaAs) nanocone (NC)-capped nanowire (NW) arrays are systematically investigated and a full light management picture is presented. The study demonstrates that compared to shape-and environment-sensitive optical resonance modes, including leaky modes and guided longitudinal resonances, optimization of light harvesting based on light scattering is more operable to guide related device fabrication. Under this consideration, near 100% absorption above the bandgap energy is realized for GaAs NC-capped NW arrays with an effective thickness of only similar to 1000 nm through balancing antireflection and light scattering in the optical systems. Further study under oblique incidence shows that light absorption for the optimized NC-capped NW arrays is almost insensitive to the incident angle, indicating excellent omnidirectional light management in the NC-capped NW configuration.

Vertical graphene nanosheets synthesized by thermal chemical vapor deposition and the field emission properties

In this paper, we explored synthesis of vertical graphene nanosheets (VGNs) by thermal chemical vapor deposition (CVD). Through optimizing the experimental condition, growth of well aligned VGNs with uniform morphologies on nickel-coated stainless steel (SS) was realized for the first time by thermal CVD. In the meantime, influence of growth parameters on the VGN morphology was understood based on the balancing between the concentration and kinetic energy of carbon-containing radicals. Structural characterizations demonstrate that the achieved VGNs are normally composed of several graphene layers and less corrugated compared to the ones synthesized by other approaches, e.g. plasma enhanced (PE) CVD. The field emission measurement indicates that the VGNs exhibit relatively stable field emission and a field enhancement factor of about 1470, which is comparable to the values of VGNs prepared by PECVD can be achieved.

CuCr2O4@rGO Nanocomposites as High-Performance Cathode Catalyst for Rechargeable Lithium–Oxygen Batteries

Rechargeable lithium–oxygen batteries have been considered as a promising energy storage technology because of their ultra-high theoretical energy densities which are comparable to gasoline. In order to improve the electrochemical properties of lithium–oxygen batteries (LOBs), especially the cycling performance, a high-efficiency cathode catalyst is the most important component. Hence, we aim to demonstrate that CuCr2O4@rGO (CCO@rGO) nanocomposites, which are synthesized using a facile hydrothermal method and followed by a series of calcination processes, are an effective cathode catalyst. The obtained CCO@rGO nanocomposites which served as the cathode catalyst of the LOBs exhibited an outstanding cycling performance for over 100 cycles with a fixed capacity of 1000xa0mAhxa0g−1 at a current density of 200xa0mAxa0g−1. The enhanced properties were attributed to the synergistic effect between the high catalytic efficiency of the spinel-structured CCO nanoparticles, the high specific surface area, and high conductivity of the rGO.

Facile synthesis of cuprous oxide nanoparticles by plasma electrochemistry

We report on a simple plasma electrochemistry method for synthesizing cuprous oxide (Cu2O) nanoparticles in the presence of glucose. In this system, Ar plasma in contact with a NaCl solution was used as one electrode, and a Cu plate was immersed in the solution as the counter electrode. The plasma-solution interaction produced many reducing and oxidizing species which can react with the Cu ions released from the Cu electrode. Cu2O nanoparticles, with an average diameter of 22 +/- 6 nm, were formed under the competition of reducing and oxidizing reactions in the solution. The results show that the glucose added in the electrolyte strongly influences the properties of the products. Corresponding to high, medium, and low concentrations of glucose, the products were nanoparticles from amorphous Cu2O, polycrystalline Cu2O, and a mixture of polycrystalline Cu2O and Cu2Cl(OH)(3), respectively.