Noriaki Sano

Properties of carbon onions produced by an arc discharge in water

A simple method to fabricate high-quality nanoparticles including spherical carbon onions and elongated fullerene-like nanoparticles similar to nanotubes in large quantities without the use of vacuum equipment is reported. The nanoparticles are obtained in the form of floating powder on the water surface following an arc discharge between two graphite electrodes submerged in water. High-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy images confirm the presence of spherical carbon onions with diameters ranging from 4 to 36 nm. The specific surface area of the floating powder was found to be very large, 984.3 m2/g, indicating that the material is promising for gas storage. From the surface area measurements, the mean particle diameter was calculated to be 3.7 nm. This value is close to the lower limit of the carbon onions observed in HRTEM. However, closer HRTEM observations also reveal that some carbon onions are not well crystallized. The large specific surface area c...

Characterisation of carbon nano-onions using Raman spectroscopy

Characteristics of the Raman spectrum from carbon onions have been identified in terms of the position of the G peak and appearance of the transverse optic phonon peaks. Five new peaks were observed in the low wavenumber region, at about 1100, 861, 700, 450 and 250 cm−1. The origins of these peaks are discussed in terms of the phonon density of states (PDOS) and phonon dispersion curves of graphite. The curvature of the graphene planes is invoked to explain the relaxation of the Raman selection rules and the appearance of the new peaks. The Raman spectrum of carbon onions is compared with that of highly oriented pyrolytic graphite (HOPG). The strain of graphene planes due to curvature has been estimated analytically and is used to account for the downward shift of the G peak.

Fabrication of inorganic molybdenum disulfide fullerenes by arc in water

Closed caged fullerene-like molybdenum disulfide (MoS2) nano-particles were obtained via an arc discharge between a graphite cathode and a molybdenum anode filled with microscopic MoS2 powder submerged in de-ionized water. A statistical study of over 150 polyhedral fullerene-like MoS2 nano-particles in plan view transmission electron microscopy revealed that the majority consisted of 2–3 layers with diameters of 5–15 nm. We show that the nano-particles are formed by seamless folding of MoS2 sheets. A model based on the agglomeration of MoS2 fragments over an extreme temperature gradient around a plasma ball in water is proposed to explain the formation of nano-particles. 2002 Elsevier Science B.V. All rights reserved.

Controlled synthesis of carbon nanoparticles by arc in water method with forced convective jet

Forced convective jet applied onto carbon arc plasma has significant effects on the formation of carbon nanoparticles (CNPs) containing multiwalled carbon nanotubes mixed with multishelled nanoparticles produced by the “arc in water” method. There is an optimized flow rate of the convective jet that leads to the highest production yield, largest hydrodynamic diameter of the products, and the reduced crystalline defects. With the convective flow rate of 1.36 dm3/min, the highest yield and production rate of CNPs could be obtained at 48.5% and 9.32 g/h, respectively. These effects of the forced convective jet originate from the enhanced quenching of carbon clusters vaporized from graphite anode. Analysis of convective flow field subjected to the arc plasma zone is conducted to indicate that synthesis of CNPs by the arc in water method can be elaborately controlled.

High-temperature simultaneous removal of acetaldehyde and ammonia gases using corona discharge

Abstract The electrostatic precipitator (ESP) is the most prevalent application for corona as ion source. ESP is widely used in industrial dust collection and home ventilation systems for cleaning gas streams. However, ESP has not been used to remove gas pollutants from a gas stream. Electron attachment is one of the promising techniques for gas purification. Electron attachment reactions occur when low-energy electrons generated in a corona-discharge reactor are captured by electronegative impurities such as acetaldehyde and fine particles to produce negative ions and charged particles. The negative ions and charged particles drift in the electric field to the anode (reactor wall) and are removed by deposition there. Moreover, O¯, O radical, ozone, and OH¯ are also generated when the carrier gas is humid air. These anions and radicals also contribute to the removal efficiency. Though acetaldehyde (CH3CHO) and ammonia (NH3) are emitted at high temperature from a crematory furnace, there is insufficient report on the effect of high temperature and simultaneous removal. The present research experimentally investigates the technical feasibility of using corona discharge reactions to treat high-temperature exhaust gas containing acetaldehyde and ammonia. The simultaneous removal efficiency of these gases from nitrogen and air is obtained experimentally. The experimental results reveal that the presence of oxygen does significantly enhance the overall removal efficiency. Similarly, it is found that the presence of water vapor also enhances the removal efficiency of the target gases from the nitrogen–oxygen mixture. The generation of undesirable byproducts such as NOx is also investigated. The present technique should be applicable to the simultaneous removal of different nanoparticles at high efficiency.

Production of carbon nanoparticles using pulsed arc discharge triggered by dielectric breakdown in water

This paper describes a simple production method for carbon nanoparticles by pulsed arc discharge in water, which is triggered by the electrical breakdown of water between graphite electrodes. High-resolution transmission electron microscopy (HRTEM) observation revealed that the main products obtained by the proposed method were onion-like nanoparticles; while carbon nanotubes were not formed. The carbon nanoonions uniformly dispersed in water forming micron-sized aggregates. The effects of the arc discharge mode (dc or pulse) on the nanoparticle formation mechanism are discussed.

Synthesis of carbon nanohorns by a gas-injected arc-in-water method and application to catalyst-support for polymer electrolyte fuel cell electrodes

Single-wall carbon nanohorns (SWNHs) were synthesized by a gas-injected arc-in-water method with varied gas flow rate, arc current, and gas component to investigate their influence on the purity, the yield, and the structure of the products, in which the quenching rate of the carbon vapour in the optimized condition for SWNHs formation was revealed as order of mega-K s−1, and thereafter the characteristics of the as-grown SWNHs for the use of a fuel cell electrode were related with the arc current in their production.

Gas sensor using single-wall carbon nanohorns

We fabricated a gas sensor using single-walled carbon nanohorns (SWNHs) produced by the gas-injected arc-in-water method. This gas sensor consisted of agglomerated SWNHs as a coating film between Al electrodes on a glass substrate and the shift of the electric resistance of this coating film caused by gas adsorption was monitored. Its sensing property was examined for the detection of NH3 and O3 at room temperature. It was confirmed that the electrical resistance of the SWNHs film increases with adsorption of NH3, whereas the adsorption of O3 induced the decrease of the resistance. A model to correlate the gas concentration and the sensing property was proposed focusing on the detection of NH3 based on mono-layer adsorption and a second-order interaction of adsorbed gas molecules for charge transfer.

Gravitational Effects on Carbon Nano‐Materials Synthesized by Arc in Water

The “arc‐in‐liquid” method is a simple and inexpensive technique for the synthesis of carbon nanotubes and related nano‐materials. In this paper, we report on the synthesis of carbon nanotubes by means of the arc‐in‐water method under microgravity and normal gravity conditions. The heat of convection and two‐phase flow caused by the arc plasma are suppressed under microgravity, so the heat and fluid flow are stabilized under such conditions and a single huge bubble is generated around the electrodes. From the images captured during the experiment of the arc‐in‐liquid method, it can be observed that the bubble contained a layer of water vapor at the gas–liquid interface under microgravity conditions, and this layer blocked the carbon vapor reaching the liquid phase. Owing to this unique phenomenon, it was determined that the synthesis of carbon nanotubes by the arc‐in‐water method is strongly affected by gravity.

A Novel Rotary Drum Filtering Photoreactor for Wastewater Treatment Using Titanium Dioxide Nanoparticles

A rotary drum filtering photoreactor using titanium dioxide (TiO2) as photocatalyst could eliminate the problem of catalyst loss by elutriation with the effluent stream. The effects of operating conditions, namely, rotating speed and filtration velocity on phenol removal were investigated. The experimental results revealed that the rates of phenol decomposition and total organic carbon (TOC) depletion decreased against the increased rotating speed. The suitable speed of the drum was 5 rpm. As for the filtration velocity, the phenol decomposition and TOC depletion rates achieved their maxima when the filtration velocity was 0.73 cm min-1. To obtain the intrinsic capacity of TiO2 cake in degrading phenol, the photolysis of phenol was also studied. The results indicated that the photolysis efficiency of phenol after 360 min was 4.96% while the decomposition efficiency of phenol was 21.47%. They indicated that the presence of TiO2 cake was a key factor for degrading phenol. In addition, the dark adsorption of phenol on TiO2 cake after 30 min was insignificant at about 0.95%.