Effect of pH on Hydrogen Evolution Yield from Water Dispersing Titania Nanoparticles Enhanced by Gamma Ray
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Effect of pH on Hydrogen Evolution Yield from Water Dispersing Titania Nanoparticles Enhanced by Gamma Ray
Satoshi Seino, Takao A. Yamamoto, Ryosuke Fujimoto, Kensuke Hashimoto, Masahiro Katsura, Shuichi Okuda1, Kenji Okitsu2 Department of Nuclear Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan. 1 Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan 2 Japan Science and Technology Corporation, 4-1-8 Hon-cho, Kawaguchi, Saitama 332-0012, Japan
ABSTRACT Hydrogen gas evolution from water dispersing nanoparticles induced by 60Co gamma-ray irradiation was studied. Nanoparticle of TiO 2 with average size of 30 nm was examined. It was indicated that the hydrogen yields were affected significantly by pH of the dispersion. Difference in agglomeration could explain the difference in hydrogen yields. Reactions that enhance the hydrogen yields were discussed, and it was concluded that the radiolysis process is dominant in the total enhancement mechanism. INTRODUCTION Hydrogen evolution yield from water irradiated with γ-ray is drastically enhanced by addition of some kinds of nanoparticles, e.g., TiO2 and Al2O2 [1-6]. However, the enhancement mechanism is not thoroughly understood yet, and is of much interest from scientific viewpoint. We have reported effects of total absorbed dose, dose rate, chemical species of nanoparticle material, sizes of primary particle and agglomerate on the hydrogen evolution yield [1-5]. On the basis of these experimental results, the enhancement mechanism was discussed taking account of radiolysis process and photocatalytic process, and the former seemed to participate much more in the enhancement [5]. In this paper, we report on results of experiments performed for investigating effect of pH on the hydrogen yield. We also investigated effect of agglomeration. These results are discussed by checking their consistency with the mechanism that we have proposed. EXPERIMENTAL Nanoparticle material of TiO2 produced with the physical vapor synthesis method was supplied by Nanophase Tech. Corp. (abbreviated as NT below). Shape and size of the primary particles were investigated with a transmission electron microscope (TEM) and found to be practically of spherical shape and obey the log-nominal distribution, reflecting its processing procedure [3]. Average diameter of primary particle was 30 nm. X-ray diffraction measurements indicated that NT-TiO2 was mainly of anatase and few % of rutile. Generally, nanoparticles in water dispersion are not necessarily monodispersive and usually form agglomerates composed of many primary particles. We evaluated average diameter of the
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agglomerates by an analyzer, based on the laser-doppler method, Microtrac UPA 150. The nanoparticle material was dispersed in distilled water in a glass vial. In advance to γray irradiation Ar gas purged gaseous species in the free space in the vial and dissolved in water. The pH of the dispersion was controlled by addition of phosphoric acid o
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