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Materials 2018, 11(7), 1202; https://doi.org/10.3390/ma11071202

Proton-Enhanced Dielectric Properties of Polyoxometalates in Water under Radio-Frequency Electromagnetic Waves

1
School of Materials and Chemical Technology Tokyo Institute of Technology, Ookayama 2-12-1 E4-3, Meguro, Tokyo 152-8550, Japan
2
Department of Marine Resource Science, Faculty of Agriculture and Marine Science, Kochi University, Monobe-otsu 200, Nankoku 783-8502, Japan
3
Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji 611-0011, Japan
4
Department of Information and Communication Systems Engineering, Okinawa National College of Technology, 905 Henoko, Nago-shi, Okinawa 905-2192, Japan
*
Author to whom correspondence should be addressed.
Received: 4 June 2018 / Revised: 5 July 2018 / Accepted: 11 July 2018 / Published: 13 July 2018
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Abstract

Electromagnetic waves, such as microwaves, have been used to enhance various chemical reactions over polyoxometalates. The dielectric properties of catalysts are among the relevant parameters facilitating catalytic reactions under electromagnetic radiation. This study describes the dielectric properties of polyoxometalate catalysts in aqueous and organic solutions to understand the mechanism of interactions between polyoxometalates and electromagnetic waves. Specific loss factors of polyoxometalates were observed at lower frequencies (<1 GHz) by the ionic conduction of the polyoxometalate solution. The evolution of ionic conduction depended strongly on cations rather than anions. Proton-type polyoxometalates exhibited significantly higher loss factors than other cations did. The activation energy for ionic conduction in protonated silicotungstic acid (H4SiW12O40) was significantly low in water (7.6–14.1 kJ/mol); therefore, the high loss factor of protonated polyoxometalates in water was attributed to the proton relay mechanism (i.e., Grotthuss mechanism). The results suggested that the proton relay mechanism at the radio-frequency band is critical for generating selective interactions of polyoxometalates with applied electromagnetic fields. View Full-Text
Keywords: polyoxometalate; dielectric spectroscopy; radio frequency; proton relay polyoxometalate; dielectric spectroscopy; radio frequency; proton relay
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Tsubaki, S.; Hayakawa, S.; Ueda, T.; Mitani, T.; Suzuki, E.-I.; Fujii, S.; Wada, Y. Proton-Enhanced Dielectric Properties of Polyoxometalates in Water under Radio-Frequency Electromagnetic Waves. Materials 2018, 11, 1202.

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