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Journal Articles

Application of high-energy-resolution X-ray absorption spectroscopy at the U L$$_{3}$$-edge to assess the U(V) electronic structure in FeUO$$_{4}$$

Yomogida, Takumi; Akiyama, Daisuke*; Ouchi, Kazuki; Kumagai, Yuta; Higashi, Kotaro*; Kitatsuji, Yoshihiro; Kirishima, Akira*; Kawamura, Naomi*; Takahashi, Yoshio*

Inorganic Chemistry, 61(50), p.20206 - 20210, 2022/12

 Times Cited Count:1 Percentile:39.57(Chemistry, Inorganic & Nuclear)

FeUO$$_{4}$$ was studied to clarify the electronic structure of U(V) in a metal monouranate compound. We obtained the peak splitting of HERFD-XANES spectra utilizing high-energy-resolution fluorescence detection-X-ray absorption near edge structure (HERFD-XANES) spectroscopy at the U L$$_{3}$$-edge, which is a novel technique in the U(V) compounds. Theoretical calculations revealed that the peak splitting was caused by splitting the 6d orbital of U(V). Such distinctive electronic states are of major interest to researchers and engineers working in various fields, from fundamental physics to the nuclear industry and environmental sciences for actinide elements.

Journal Articles

Electronic effects of nitrogen atoms of supports on Pt-Ni rhombic dodecahedral nanoframes for oxygen reduction

Kato, Masaru*; Nakahoshiba, Ryota*; Ogura, Kazuya*; Tokuda, Shoichi*; Yasuda, Satoshi; Higashi, Kotaro*; Uruga, Tomoya*; Uemura, Yohei*; Yagi, Ichizo*

ACS Applied Energy Materials (Internet), 3(7), p.6768 - 6774, 2020/07

To understand electronic effects of nitrogen-doped and polymer-coated carbon supports on the catalytic activity of Pt-based nanostructured catalysts, we prepared Pt$$_{3}$$Ni nanoframes (NFs) supported on polybenzimidazole (PBI)-coated and uncoated carbon nanotubes for the oxygen reduction reaction (ORR), and then compared their catalytic activities and electronic properties with those of NFs immobilized on nitrogen-doped and undoped carbon supports. Although both PBI-coating and nitrogen-doping approaches improved the catalytic activity of NFs, ${it ex situ}$ X-ray photoelectron spectroscopy and ${it in situ}$ X-ray absorption spectroscopy revealed that nitrogen doping showed electronic effects on NFs, whereas PBI-coating showed almost no impact on the electronic state of NFs but stabilized Pt(OH)$$_{rm ad}$$ species under electrochemical conditions. Our studies demonstrate that difference in microscopic environments of nitrogen atoms at the catalyst/support interface is highly sensitive to the electronic effects of supports on Pt-based electrocatalysts.

Oral presentation

Elucidation of the reduction of uranium in biotite by advanced X-ray spectroscopy

Yomogida, Takumi; Yamada, Shinya*; Ichinohe, Yuto*; Sato, Toshiki*; Hayakawa, Ryota*; Okada, Shinji*; Toyama, Yuichi*; Hashimoto, Tadashi; Noda, Hirofumi*; Isobe, Tadaaki*; et al.

no journal, , 

The reduction of uranium on biotite was studied to obtain insight into the immobilization of uranium in the environment. The chemical species of uranium in biotite were studied using a superconducting transition edge sensor and an X-ray emission spectrometer to remove interference from rubidium in biotite. As a result, the speciation of uranium in biotite collected from former uranium deposits was possible. The XANES spectra of the biotite indicated that the uranium in the biotite was partially reduced.

Oral presentation

Speciation of uranium in artificially weathered mica by X-ray absorption spectroscopy

Yomogida, Takumi; Higashi, Kotaro*; Kawamura, Naomi*; Kitatsuji, Yoshihiro; Takahashi, Yoshio*

no journal, , 

Biotite, a layered silicate mineral, is known to be a host phase for uranium(U) in U mines. There are still many unclear factors regarding its U accumulation mechanism. In this study, U adsorption experiment was conducted on artificially weathered biotite by removing interlayer potassium. The results showed that the ratio of reduced species of U increased with increasing the K loss ratio in interlayer, indicating that U reduction occurred at cleavages developed by weathering of the biotite.

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