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180 results on '"Akiyama, Kazuhiko"'

9. Elucidating the Mechanistic Origin of a Spin State-Dependent FeNx–C Catalyst toward Organic Contaminant Oxidation via Peroxymonosulfate Activation

Author

Zhang, Bofan, Li, Xianquang, Akiyama, Kazuhiko, Bingham, Paul, and Kubuki, Shiro

Subjects
Environmental Chemistry, General Chemistry
Abstract

Atomically dispersed metals on nitrogen-doped carbon matrices have attracted extensive interest in the removal of refractory organic pollutants. However, a thorough exploration of the particular structure for each active site and specific effects of these sites still remains elusive. Herein, an Fe-pyridinic N4 structure in a single-atom catalyst (FeNx–C) was constructed using a facile pyrolysis strategy, and it exhibited superior catalytic activity in peroxymonosulfate (PMS) activation toward organic contaminant oxidation. The various Fe species and relative amounts of each Fe site in the FeNx–C catalyst were validated using X-ray absorption spectroscopy and 57Fe Mössbauer spectroscopy, which showed critical dependencies on the precursor ratio and calcination temperature. The positive correlations between relative content of high-spin state species (FeII and FeIII) and catalytic performance were found to determine the reactive species generation and electron transfer pathway in the FeNx–C/PMS system. Moreover, catalytic performance and theoretical calculation results revealed that FeII–N4 in the high-spin state (S = 2) tends to activate PMS to form sulfate and hydroxyl radicals via a one-electron transfer process, while the FeIII–N4 moiety (S = 5/2) is prone to high-valent iron species generation with lower free energy. Benefiting from finely tuned active sites, a single-atom FeNx–C catalyst achieved favorable applicability in actual wastewater treatment with efficient resistance of the common water matrix. The present work advances the mechanistic understanding of spin state-dependent persulfate activation in single-atom catalysts and provides guidance to design a superior catalyst based on spin state descriptions.

Published
2021

36. Elucidating the Mechanistic Origin of a Spin State-Dependent FeNx–C Catalyst toward Organic Contaminant Oxidation via Peroxymonosulfate Activation

Author

Zhang, Bofan, Li, Xianquan, Akiyama, Kazuhiko, Bingham, Paul A., and Kubuki, Shiro

Abstract

Atomically dispersed metals on nitrogen-doped carbon matrices have attracted extensive interest in the removal of refractory organic pollutants. However, a thorough exploration of the particular structure for each active site and specific effects of these sites still remains elusive. Herein, an Fe-pyridinic N4structure in a single-atom catalyst (FeNx–C) was constructed using a facile pyrolysis strategy, and it exhibited superior catalytic activity in peroxymonosulfate (PMS) activation toward organic contaminant oxidation. The various Fe species and relative amounts of each Fe site in the FeNx–C catalyst were validated using X-ray absorption spectroscopy and 57Fe Mössbauer spectroscopy, which showed critical dependencies on the precursor ratio and calcination temperature. The positive correlations between relative content of high-spin state species (FeIIand FeIII) and catalytic performance were found to determine the reactive species generation and electron transfer pathway in the FeNx–C/PMS system. Moreover, catalytic performance and theoretical calculation results revealed that FeII–N4in the high-spin state (S= 2) tends to activate PMS to form sulfate and hydroxyl radicals via a one-electron transfer process, while the FeIII–N4moiety (S= 5/2) is prone to high-valent iron species generation with lower free energy. Benefiting from finely tuned active sites, a single-atom FeNx–C catalyst achieved favorable applicability in actual wastewater treatment with efficient resistance of the common water matrix. The present work advances the mechanistic understanding of spin state-dependent persulfate activation in single-atom catalysts and provides guidance to design a superior catalyst based on spin state descriptions.

Published
2022
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37. A C82 carbon cage stable toward two different oxidation states of endohedral metal atoms

Author

Sueki, Keisuke, Akiyama, Kazuhiko, Koiuchi, Kikuchi, and Nakahara, Hiromichi

Subjects
Carbon allotropes -- Research, Radioactive decay -- Research, Isomerism -- Research, Organometallic chemistry -- Research, Chemicals, plastics and rubber industries
Abstract

The existence of a special kind of C(sub 82) carbon cage is proven experimentally. This was done through an examination of the effect of transmutation of an encaged metal atom on the stability of M(at)C(sub 82). The carbon cage, which forms chemically stable metallofullerenes with metal atoms, is the same one that commonly forms M(at)C(sub 82)(C) with M in the +3 state. It is also the one that forms the minor isomers of M(at)C(sub 82)(C) and of Tm(at)C(sub 82)(C) for M in the +2 oxidation state.

Published
1999

40. Oxidation of element 102, nobelium, with flow electrolytic column chromatography on an atom-at-a-time scale

Author

Toyoshima, Atsushi, Kasamatsu, Yoshitaka, Tsukada, Kazuaki, Asai, Masato, Kitatsuji, Yoshihiro, Ishii, Yasuo, Toume, Hayato, Nishinaka, Ichiro, Haba, Hiromitsu, Ooe, Kazuhiro, Sato, Wataru, Shinohara, Atsushi, Akiyama, Kazuhiko, and Nagame, Yuichiro

Subjects
Chromatography -- Usage, Nobelium -- Chemical properties, Oxidation-reduction reaction -- Analysis, Chemistry
Abstract

A newly developed flow electrolytic column chromatography technique was used to successfully perform oxidation of element 102, nobelium (No), on an atom-at-a-time scale in 0.1 M [alpha]-hydroxyisobutyric acid ([alpha]-HIB) solution. The most stable ion, [No.sup.2+], was found to oxidize into [No.sup.3+] within 3 min and the oxidized No complex with [alpha]-HIB exhibited the trivalent state in the column above an applied potential of 1.0 V.

Published
2009

43. Absorption spectra of metallofullerenes M@C82 of lanthanoids

Author

Akiyama, Kazuhiko, Sueki, Keisuke, Kodama, Takeshi, Kikuchi, Koichi, Ikemoto, Isao, Nakahara, Hiromichi, and Katada, Motomi

Subjects
Toluene -- Chemical properties, Toluene -- Optical properties, Chemistry, Physical and theoretical -- Research, Absorption spectra -- Usage, Chemicals, plastics and rubber industries
Abstract

The UV/vis/NIR spectra of 10 kinds of dissolved in toluene and the molar absorption coefficients is determined for each absorption peak. The findings indicate that the oscillator strengths for the 986 and 1406 nm absorption are about 1 order of magnitude smaller and those of the 986 nm absorption vary appreciably as the degree of filling of the 4f orbital changes.

Published
2000

46. Synthesis of Tetra(3‐thienyl)biphenoquinone and its Charge Transfer Complex with Perylene.

Author

Fujii, Ryotaro, Hossain, Md. Awlad, Akimoto, Hisato, Hirabayashi, Kazunori, Shimizu, Toshio, Akiyama, Kazuhiko, Goto, Kenta, Nishikawa, Hiroyuki, Yamashita, Ken‐ichi, and Sugiura, Ken‐ichi

Subjects
QUINONE, OXIDATIVE coupling, HETEROCYCLIC compounds
Abstract

Abstract: Tetra(thienyl)biphenoquinones were designed and synthesized. An oxidative coupling of 2,6‐bis(3‐thienyl)phenol with PbO2 in acetic acid afforded the corresponding biphenoquinone along with 2,6‐bis(3‐thienyl)‐p‐benzoquinone. This biphenoquinone showed properties characteristic of a π‐expanded quinone, that is, positively shifted reduction potential and light absorption in the visible region. In contrast to kinetically protected biphenoquinones with bulky substituents at the ortho‐positions of carbonyls, the title compounds take a planar structure because of the small steric repulsion of the five‐membered thiophene rings. Its charge transfer complex with perylene is characterized by a well‐overlapped mixed stack. [ABSTRACT FROM AUTHOR]

Published
2018
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48. Isolation and characterization of light actinide metallofullerenes

Author

Akiyama, Kazuhiko, Zhao, Yuliang, Sueki, Keisuke, Tsukada, Kazuaki, Haba, Hiromitsu, Nagame, Yuichirou, Kodama, Takeshi, Suzuki, Shinzou, Ohtsuki, Tsutomu, Sakaguchi, Masahiko, Kikuchi, Koichi, Katada, Motomi, and Nakahara, Hiromichi

Subjects
Actinide elements -- Research, Carbon allotropes -- Research, Organometallic compounds -- Research, Chemistry
Abstract

The production of light actinide metallofullerenes is described.

Published
2001

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