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巻・号	3巻3号	ページ	235
記事分類・特集	原報
題目(和文)	酸化亜鉛の光触媒能の研究
著者	藤田勇三郎
要旨(英文)	The effect of illumination on the oxygen adsorbed on various zinc oxide samples was investigated using near ultra-violet light. Reversible photodesorption of oxygen was found to occur on highly outgassed zinc oxide which was prepared by igniting zinc carbonate and denoted as ZnO I. On the other hand, the photoresponse turned to be an irreversible photoadsorption when the zinc oxide sample was subjected to oxidation in an oxygen atmosphere. In either case, the effective wave length of the light nearly coincided with that of the characteristic absorption of zinc oxide. Initial rates of these photoresponses were observed against light intensity, oxygen pressure and temperature.The mechanism of the photoresponse was investigated after Wolkenstein's method with particular interest in the reversal effect, i. e., photoresponses were discussed in connection with recombination processes of optically created charge carriers through the surface level of adsorbed oxygen. Thus, it became apparent that the relative height of Fermi level of a given zinc oxide sample to the surface level of adsorbed oxygen is important as to whether photodesorption or photoadsorption should appear on illumination. Additional experiments were carried out on the basis of the mechanism using zinc oxide samples doped with impurities such as alumina or lithium oxide, and found to be compatible with the theoretical expectation.The effect of illumination on the catalytic oxidation of carbon monoxide was investigated. A zinc oxide sample supplied by Kanto Kagaku K.K. was used throughout experiments, the sample being denoted as ZnO 2. Photocatalytic oxidation of carbon monoxide was found to occur with the light near ultra-violet at 100-200℃ while no reaction was perceptible in the absence of light in this tem-perature interval. The rate of the photocatalytic reaction was expressed by ν= k PO2 0.6 Pco0. The temperature coefficient was found to be 2.3 kcal. The photocatalytic oxidation of carbon monoxide was described to appear via photoenhanced adsorption of oxygen on the catalyst surface since the photoeffect on the present ZnO 2-O2 system turned out always to be adsorption. Neither outgassing nor reduction in a carbon monoxide atmosphere below 500℃ gave rise to photodesorption in contrast with ZnO I. The pretreatment of the zinc oxide sample was found, however, to affect the photocatalytic activity toward the oxidation of carbon monoxide. Based on such photokinetic behavior, photo-catalytic mechanism of the oxidation of carbon monoxide was postulated and discussed.The liquid phase oxidation of isopropyl alcohol was investigated in the presence of ZnO 2. The oxidation reaction conducted at 65℃ was markedly accelerated when illuminated by the light near ultra-violet, the products being exclusively acetone and hydrogen peroxide. The photocatalytic ultra-violet, the products being exclusively acetone and hydrogen peroxide. The photocatalytic avtivity was sensitively dependent again on the pretreatment of the zinc oxide sample. On outgassed ZnO 2, the consumption of oxygen took place on illumination while it stopped on interrupting the light. On untreated ZnO 2, on the other hand, the consumption of oxygen did not stop on interrupting the light. Moreover, it continued rather acceleratingly with the progress of the reaction. This apparently peculiar phenomena were interpreted as that adsorbed oxygen produced by the decomposition of hydrogen peroxide takes part simultaneously in the chain initiation of the reaction in the case of untreated ZnO 2 while photoadsorbed oxygen was the sole chain initiator on outgassed ZnO 2. Adsorbed oxygen produced from the decomposition of hydrogen peroxide was considered to prevail in a later stage of the reaction, hence giving rise to dark reaction.
発行年月日	2016-12-01	公開日	2016-12-01
パーマリンク	https://catsj.jp/jnl/pageview?articlecd=0303023500j