Tatsuo Kanki

Development of TiO2 photocatalyst reaction for water purification

Abstract A new type of tubular photocatalytic reactor was developed to realize practical application of TiO 2 photocatalyst for water purification. The principal part of the reactor consists of the ceramic cylindrical tube whose inner surface is coated with Pt-loaded TiO 2 film and the 30 W ultraviolet light lamp which is set longitudinally in the center of the tube. The water to be treated is circulated through the reactor via a buffer reservor for aeration. The performance of the reactor was evaluated through the experiment of decomposing aqueous phenol, tetrachloroethylene (TCE) and bisphenol A. It was shown that all the tested organic compounds are decomposed in moderately shorter time by the reactor. It would be expected that the reactor could be commercialized for its high efficiency in purifying polluted water and for its simple set up ensuring maintenance free.

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.

Photocatalytic reduction and deposition of metallic ions in aqueous phase

Experiment of photochemical reduction and deposition of cupric ion by titanium dioxide photocatalyst was carried out. The TiO2 particles were suspended in the aqueous solution of copper sulphate where sodium formate was added as a hole scavenger. It was shown that cupric ion can be reduced and deposited on TiO2 surface very rapidly when the TiO2 particles are embedded at adequately higher densities and formic acid is added at moderate concentrations comparative to or higher than that of cupric ion. The deposition rate depends strongly on the concentration of sodium formate: it increases as the concentration increases. The mechanism of reduction reaction was estimated by the elementary reactions and the adsorption of formic anion. The practical deposition rates can be successfully explained by assuming that the oxidation reaction step of adsorbed formic anion is rate controlling, with the remaining steps being all instantaneously fast. Possibility of photochemical reduction of chromium ion(VI) to nontoxic chromium ion(III) or to metal chromium was also investigated.

Photocatalytic degradation of organic compounds in aqueous solution by a TiO2-coated rotating-drum reactor using solar light

Abstract This paper deals with the degradation of aqueous phenol by a newly proposed rotating-drum reactor coated with a TiO2 photocatalyst, in which TiO2 powders loaded with Pt are immobilized on the outer surface of a glass-drum. The reactor can receive solar light and oxygen from the atmosphere effectively. It was shown experimentally that phenol can be decomposed rapidly by this reactor under solar light: with our experimental conditions the phenol with an initial concentration of 22.0 mg/dm3 was decomposed within 60 min and was completely mineralized through intermediate products within 100 min. The photonic efficiency under solar light was shown to take the value 0.00742 mol-C/Einstein. The photocatalytic decomposition processes of phenol by this reactor were also discussed on the basis of the Langmuir–Hinshelwood kinetic model.

Pressure effects on nanotubes formation using the submerged arc in water method

Synthesis of multi-walled carbon nanotubes (MWCNTs) by an arc discharge between two graphite electrodes submerged in water under controlled pressure (from 400 to 760 Torr) is reported. Transmission and scanning electron microscopy investigations of the arc discharge product collected from the bottom of the reactor revealed high concentrations of MWCNTs at all pressures. Dynamic light scattering (DLS) on suspensions containing MWCNTs showed that the mean diameter of the nanotubes increases with decreasing pressure. Raman spectroscopy analysis reveals that the relative amount of disordered carbon is significantly less in the low-pressure samples. Furthermore, the yield of the deposit was found to be independent of the pressure. These results suggest that the physical properties of MWCNTs formed by the submerged arc can be controlled by varying the pressure.

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.

Influence of dissolved inorganic additives on decomposition of phenol and acetic acid in water by direct contact of gas corona discharge

Abstract The influence of dissolved several inorganic contaminants into water was examined on the decomposition of aqueous organic compounds by direct contact of gas corona discharge. It was found that addition of 0.01 mol l −1 NaOH into water significantly improves the decomposition of aqueous phenol while the addition of HCl of the same concentration inhibits the decomposition rate. As it is known that phenol is converted to stable acetic acid during the decomposition process in the reactor, the influence of NaOH, HCl, H 3 PO 4 and NaCl was examined on the degradation of acetic acid. As a result, dissolved Cl − inhibits its decomposition efficiency. It is also found that this decomposition rate is significantly improved by raised pH which is higher than 11.

Surface active species and their reaction schemes in extraction solution systems identified from practical behaviors of interfacial tension

Abstract The interfacial tensions in two-phase solution systems for extraction of metallic ions from aqueous phase to organic phase by di(2-ethyl-hexyl) phosphoric acid were measured by the Wilhelmy plate method and partly by laser-light scattering method to confirm the accuracy. For copper and iron extraction solution systems, the surface-active species and their interfacial concentrations were identified by comparing the actual behavior of interfacial tension, the pH and extractant concentration dependencies, with the Gibbs–Langmuir equation for adsorption. It was shown that the extractant molecules should be adsorbed at the interface in the form of monomer and its dehydrogenated anion and that in copper extraction solution system non-surface-active 1:2 intermediate complexes should be formed, and in iron extraction solution system strongly surface-active 1:2 intermediate complexes should be formed at the interface. Based on the insights related to the intermediate complexes, reaction schemes at the interface are also discussed.

On thermophoresis of relatively large aerosol particles suspended near a plate

Abstract Thermal creep flow of a gas around a spherical particle of an arbitrary thermal conductivity suspended near a plate is analyzed, neglecting shear velocity slip. The thermal force acting on the particle at an arbitrary distance from the plate is given as a function of ratio of the thermal conductivity of the particle to that of the gas. Effects of the collector plate on the drift velocity of a precipitating particle are clarified.

Diffusion of rarefied gas mixtures in a circular tube under the existence of pressure gradients

A simple and general expression for nonuniform pressure diffusion of a binary mixture in a circular tube is obtained by applying locally uniform distributions of molecular velocity plus a new physical model on the molecular transport of momentum in the Knudsen layer, which is derived from the momentum balance considerations including the influence of wall interactions of molecules, to Maxwell’s transport equation. The theory predicts some striking phenomena, the Kramers–Kistemaker pressure effect, the Hoogschagen flux ratio, Knudsen minimum, and so on. In order to check the validity of the theory, the flux of a component gas in the Stefan tube and the pressure difference which accompanies it are determined experimentally for Hg‐He and Hg‐Ar mixtures and found to be in good agreement with those predicted from theory.