Atsushi Toyoda

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.

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.

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.