Decontamination of Tritiated-Water Using Super-hydrophobic Pt-Catalyst Synthesized with Water-in-Supercritical CO{sub 2}

Conference · Tue Jan 15 04:00:00 EST 2008

OSTI ID:21144241

Enokida, Youichi; Sawada, Kayo ^[1]; Shimizu, Ryosuke ^[1]; Yamamoto, Ichiro ^[2]

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1. EcoTopia Science Institute (Japan)
2. Graduate School of Engineering, Nagoya University, 1 furo-cho, Nagoya 463-8603, Aichi-ken (Japan)

Tritium, {sup 3}H, is one of the hydrogen isotopes, created in coolant of a fission reactor and to be utilized as fuel for nuclear fusion reactors. Since a large amount of tritium will be contained in a fusion reactor or in a fission reactor, a small fraction of the tritiated chemical species, in most cases, tritiated water, may leak to the environment. Tritium is, however, a radioactive isotope whose specific radioactivity is 4 x 10{sup 17} Bq kg{sup -1}, and easy to transfer in human body, its confinement is very important from the safety aspect. One of the problems of tritium confinement and decontamination of tritiated chemical species is related with necessity of its isotope separation from lighter hydrogen isotopes, {sup 2}H and {sup 1}H. Most of principles for the isotope separations are based on fractionations of isotopes in different chemical species. A large fractionation for hydrogen isotopes is observed in a chemical exchange of hydrogen atoms between water, Q{sub 2}O, and hydrogen gas, Q{sub 2}, where 'Q' denotes one of the hydrogen isotopes. Heavier isotopes are enriched significantly into Q{sub 2}O rather than Q{sub 2}. Therefore practical method of tritium removal would be established by hydrogen isotope separation with chemical exchange of water and hydrogen gas. At first, we prepared a catalyst, by reducing Pt{sup 4+} in reversed micelles where the reducing agent, aqueous solution of sodium tetra borohydrate, NaBH{sub 4} was also contained in reversed micelles prepared separately. In this situation, micelles containing Pt{sup 4+} and reducing reagent collided and produced Pt nanoparticles, which were expected to be impregnated in the hydrophobic structure after depressurization. After this type of earlier experiment we determined a mass of impregnated Pt by total dissolution of gauze with aqua regia followed by concentration measurement of Pt with ICP-AES. We performed several trials, unfortunately, however, the mass of Pt deposited on the gauze was very small to detect, and this approach turns to be not successful. As the second approach, we utilize CO{sub 2} soluble Pt precursor, CODMe{sub 2}Pt purchased from Sigma-Aldrich Co. and H{sub 2} gas as reducing agent, which could be completely mixed with SC-CO{sub 2}. This system was well-known for Pt particle formation by auto-catalytic growth. The second approach was aiming at increasing Pt amount deposited in the gauze. This approach was successful in increasing Pt amount, but the Pt particle size also increased to be more than 50 nm, which was not suitable for catalyst. Finally, we synthesized the catalyst by the following procedure: firstly, a reducing agent of NaBH{sub 4} was deposited on the nano-textured hydrophobic layer on the gauze. This step was realized by forming reversed micelles of aqueous NaBH{sub 4} solution using a surfactant AOT and a co-surfactant 2,2,3,3,4,4,5,5,-octafluoro-1-pentanol (F-pentanol) in SC-CO{sub 2}. This system of surfactant combination of AOT and F-pentanol has been found to work successfully in recent studies. In the second step, the gauze was contacted with CODMe{sub 2}Pt dissolved in SC-CO{sub 2} to synthesize seeds of Pt particles for the auto-catalytic reaction proceeding by CODMe{sub 2}Pt with hydrogen. The seeds were formed by the reaction between deposited NaBH{sub 4} and CODMe{sub 2}Pt in SC-CO{sub 2}. The physical characterization of this catalyst was performed by SEM-EDS. By this procedure, the Pt hydrophobic catalyst where Pt nanoparticle of 10 nm in diameter was locally deposited in the nano-textured layer was successfully prepared. Hydrophobicity after the chemical Pt deposition was tested by measurement of water absorbed on the gauze and the catalyst performance was evaluated by {sup 1}H{sup 2}H formation through the scrambling reaction from {sup 1}H{sub 2} and {sup 2}H{sub 2} and the reaction was successfully observed. We demonstrated a new hydrophobic catalyst preparation using SC-CO{sub 2} effectively. We can conclude that the approach of creating Pt nanoparticles in SC-CO{sub 2} and depositing them in the super-hydrophobic structure on the metal surface is useful for synthesizing hydrophilic catalysts for the hydrogen isotope separation.

• Research Organization: American Nuclear Society, 555 North Kensington Avenue, La Grange Park, Illinois 60526 (United States)
• OSTI ID: 21144241
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
AQUEOUS SOLUTIONS
AUGER ELECTRON SPECTROSCOPY
CARBON DIOXIDE
CATALYSTS
DECONTAMINATION
DEUTERIUM
HYDROGEN 1
PLATINUM IONS
REDUCING AGENTS
SAFETY
SCANNING ELECTRON MICROSCOPY
TRITIUM
TRITIUM OXIDES