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論文

Laser heating induced spatial homogenization of phase separated Na$$_{2}$$O-B$$_{2}$$O$$_{3}$$-SiO$$_{2}$$ glass plate with bearing NiO for heat center and structural probe

富田 夏奈*; 岸 哲生*; 松村 大樹; 矢野 哲司*

Journal of Non-Crystalline Solids, 597, p.121891_1 - 121891_10, 2022/12

 被引用回数:0 パーセンタイル:0.02(Materials Science, Ceramics)

Na$$_{2}$$O-B$$_{2}$$O$$_{3}$$-SiO$$_{2}$$ glass plate phase separated in spinodal was partially remelted and homogenized by laser heating. As heat generation source, 0.8 mol% NiO was added to absorb continuous-wave laser with $$lambda$$=1064 nm. After acid leaching, borate phase with NiO was remaining partially in laser irradiated area. X-ray Absorption Fine Structure (XAFS) spectra revealed that Ni$$^{2+}$$ in laser irradiated area showed coordination change from 6 coordinated octahedral to 5 coordinated in square pyramid along with apparent color change from green to brown. Similar change was observed in water-quenched specimen from 1000$$^{circ}$$C. Ni$$^{2+}$$ transition gave additional structural information in phase separate / homogeneous glass, which was difficult to be distinguished by spectroscopy which focuses on covalent bonding of glass network.

論文

Synergistic hybrid electrocatalysts of platinum alloy and single-atom platinum for an efficient and durable oxygen reduction reaction

Liu, B.*; Feng, R.*; Busch, M.*; Wang, S.*; Wu, H.*; Liu, P.*; Gu, J.*; Bahadoran, A.*; 松村 大樹; 辻 卓也; et al.

ACS Nano, 16(9), p.14121 - 14133, 2022/09

Pt single-atom materials possess an ideal atom economy but suffer from limited intrinsic activity and side reaction of producing H$$_{2}$$O$$_{2}$$ in catalyzing the oxygen reduction reaction (ORR). Here, we demonstrate that anchoring platinum alloys on single-atom Pt-decorated carbon (Pt- SAC) surmounts their inherent deficiencies, thereby enabling a complete four-electron ORR pathway catalysis with high efficiency and durability. Pt$$_{3}$$Co@Pt-SAC demonstrates an exceptional mass and specific activities 1 order of magnitude higher than those of commercial Pt/C. They are durable throughout 50000 cycles, showing only a 10 mV decay in halfwave potential. The superior durability is attributed to the shielding effect of the Pt-SAC coating, which significantly mitigates the dissolution of Pt$$_{3}$$Co cores.

論文

Displacement of hydrogen position in di-hydride of V-Ti-Cr solid solution alloys

榊 浩司*; Kim, H.*; Majzoub, E. H.*; 町田 晃彦*; 綿貫 徹*; 池田 一貴*; 大友 季哉*; 水野 正隆*; 松村 大樹; 中村 優美子*

Acta Materialia, 234, p.118055_1 - 118055_10, 2022/08

 被引用回数:0 パーセンタイル:0(Materials Science, Multidisciplinary)

Local structure in the di-hydride phases of V-Ti-Cr solid solution alloys were investigated using synchrotron X-ray and neutron total scattering experiments. Both Rietveld refinement and pair distribution function (PDF) refinement of the X-ray scattering data indicated that the crystal structure of the metal lattice was a face centered cubic (FCC) structure and no difference between their local structure and average structure was observed. However, the CaF$$_{2}$$ structure model did not reproduce the first peak corresponding to the metal-hydrogen correlation in neutron PDF patterns. When special quasi-random structure (SQS) models are applied for the refinements, the whole neutron PDF patterns were reproduced. Distribution of interatomic distances between hydrogen and metal atoms in the relaxed SQS models showed that interatomic distance of hydrogen with Cr was shorter than that with V and that with Ti was longer than that with V, independently of the chemical compositions.

論文

Operando Br K-edge dispersive X-ray absorption fine structure analysis for Br$$^{-}$$/Br$$_{3}$$$$^{-}$$ redox mediator for Li-Air batteries

伊藤 仁彦*; 松村 大樹; Song, C.*; 久保 佳美*

ACS Energy Letters (Internet), 7(6), p.2024 - 2028, 2022/06

 被引用回数:0 パーセンタイル:0.01(Chemistry, Physical)

The behavior of Br$$^{-}$$/Br$$_{3}^{-}$$ redox mediator (RM), which has been shown to suppress charging overpotential in lithium-air batteries, has been detected for the first time using operando Br K-edge dispersive X-ray absorption fine structure. Br$$_{3}^{-}$$ ions in the electrolyte increase monotonically after $$sim$$ 30% charging, which indicates that a part of Br$$_{3}^{-}$$ formed via the oxidation of Br$$^{-}$$ during charging does not oxidize Li$$_{2}$$O$$_{2}$$ as RM but gets accumulated in the cell. Consistent with this result, the O$$_{2}$$ evolution efficiency gradually decreases from the initial 100% as the charging progresses, and CO$$_{2}$$ is emitted at the end of the charging. All these results clearly show that the Br$$^{-}$$/Br$$_{3}^{-}$$ RM functions effectively at the beginning of charging but gradually loses its function as charging proceeds.

論文

Uranium chelating ability of decorporation agents in serum evaluated by X-ray absorption spectroscopy

上原 章寛*; 松村 大樹; 辻 卓也; 薬丸 晴子*; 田中 泉*; 城 鮎美*; 齋藤 寛之*; 石原 弘*; 武田(本間) 志乃*

Analytical Methods, 14(24), p.2439 - 2445, 2022/06

 被引用回数:1 パーセンタイル:77.26(Chemistry, Analytical)

Internal exposure to actinides such as uranium and plutonium has been reduced using chelating agents for decorporation because of their potential to induce both radiological and chemical toxicities. This study measures uranium chemical forms in serum in the presence and absence of chelating agents based on X-ray absorption spectroscopy (XAS). The chelating agents used were 1-hydroxyethane 1,1-bisphosphonate (EHBP), inositol hexaphosphate (IP6), deferoxamine B (DFO), and diethylenetriaminepentaacetate (DTPA). The main ligands forming complexes with uranium in the serum were estimated as follows: IP6 $$>$$ EHBP $$>$$ bioligands $$>$$ DFO $$>>$$ DTPA when the concentration ratio of the chelating agent to uranium was 10. Measurements of uranium chemical forms and their concentrations in the serum would be useful for the appropriate treatment using chelating agents for the decorporation of uranium.

論文

Influences of hydration-dehydration on local structure in layered perovskite LaSr$$_{3}$$Fe$$_{3}$$O$$_{10}$$

八木 祐太朗*; 脇田 雄大*; 籠宮 功*; 松江 郁弥*; 柿本 健一*; 松村 大樹; 米田 安宏

ChemistrySelect (Internet), 7(21), p.e202104575_1 - e202104575_7, 2022/06

 被引用回数:0 パーセンタイル:0(Chemistry, Multidisciplinary)

The layered perovskite LaSr$$_{3}$$Fe$$_{3}$$O$$_{10}$$ (LSF) easily hydrates under ambient air. The hydrated LSF transports hydroxides in the middle-temperature range of 100 $$^circ$$C - 250 $$^circ$$C. This study used X-ray absorption fine structure analysis on normal and hydrated LSF from room temperature to 350 $$^circ$$C to evaluate the relationship between local structures and ion transport characteristics. The H$$_{2}$$O molecules are mainly intercalated into rock-salt interlayers, which are close to the La1 and O3 sites. The generated OH$$^{-}$$ ions are found at O3 sites, which are closer to Sr ions than La ions. The intercalated H$$_{2}$$O molecules and formed OH$$^{-}$$ ions expand the spaces of the rock-salt interlayers. The temperature dependence of the local crystal structure was also studied in this study. According to the findings, the presence of OH$$^{-}$$ ions on the O3 sites, which are closer to Sr ions, plays a significant role in OH$$^{-}$$ transport in the medium temperature range.

論文

Repeatable photoinduced insulator-to-metal transition in yttrium oxyhydride epitaxial thin films

小松 遊矢*; 清水 亮太*; 佐藤 龍平*; Wilde, M.*; 西尾 和記*; 片瀬 貴義*; 松村 大樹; 齋藤 寛之*; 宮内 雅浩*; Adelman, J. R.*; et al.

Chemistry of Materials, 34(8), p.3616 - 3623, 2022/04

 被引用回数:3 パーセンタイル:66.25(Chemistry, Physical)

Here, we demonstrate such a highly repeatable photoinduced insulator-to-metal transition in yttrium oxyhydride (YO$$_{x}$$H$$_{y}$$) epitaxial thin films. The temperature ($$T$$) dependence of the electrical resistivity ($$rho$$) of the films transforms from insulating to metallic ($$drho/dT > 0$$) under ultraviolet laser illumination. The sample is heated (125 $$^{circ}$$C) under an Ar atmosphere to recover its original insulating state. The films recover their original metallic conductivity when subsequently subjected to ultraviolet laser illumination, showing repeatable photoinduced insulator-to-metal transition. First principles calculations show that the itinerant carriers originate from the variations in the charge states of the hydrogen atoms that occupy octahedral interstitial sites. This study indicates that tuning the site occupancy (octahedral/tetrahedral) of the hydrogen atoms exerts a significant effect on the photoresponse of metal hydrides.

論文

Selenide [Se(-II)] immobilization in anoxic, Fe(II)-rich environments; Coprecipitation and behavior during phase transformations

Francisco, P. C. M.; 松村 大樹; 菊池 亮佑*; 石寺 孝充; 舘 幸男

Environmental Science & Technology, 56(5), p.3011 - 3020, 2022/03

 被引用回数:0 パーセンタイル:0(Engineering, Environmental)

The radionuclide selenium-79 (Se-79) is predicted to be a key contributor to the long-term radiologic hazards associated with geological high-level waste (HLW) repositories, hence its release is of pertinent concern in the safety assessment of repositories. In this study, we examined the immobilization mechanisms of Se(-II)-prevalent under anoxic and reducing repository conditions-during interaction with aqueous Fe(II) and freshly precipitated Fe(OH)$$_{2}$$ at circumneutral and alkaline conditions, respectively, its response to changes in pH, and its behavior during aging at 90$$^{circ}$$C. Using microscopic and spectroscopic techniques, we observed that Se(-II) was readily immobilized via iron selenide precipitation regardless of whether Se(-II) reacts with aqueous species or solid phases and that modifying the pH following initial immobilization did not immediately remobilize Se(-II). These observations indicate that Se(-II) migration beyond the overpack can be effectively and rapidly retarded via interaction with Fe(II) species arising from overpack corrosion. Thermodynamic calculations, however, showed that at alkaline conditions, iron selenides immediately became metastable and will likely dissolve in the long term. Aging experiments at 90$$^{circ}$$C showed that Se(-II) can be completely retained via the crystallization of ferroselite at circumneutral conditions, while it will be largely remobilized at alkaline conditions. Our results show that Se(-II) mobility can be significantly influenced by its interactions with the corrosion products of the steel overpack and that these behaviors will have to be considered in repository safety assessments.

論文

Dispersive XAFS Study on the Laser-Induced Reduction of a Rh$$^{3+}$$ ion complex; Presence of a Rh$$^{+}$$ Intermediate in Direct Photoreduction

佐伯 盛久*; 松村 大樹; 中西 隆造*; 蓬田 匠; 辻 卓也; 齋藤 寛之*; 大場 弘則*

Journal of Physical Chemistry C, 126(12), p.5607 - 5616, 2022/03

 被引用回数:1 パーセンタイル:66.25(Chemistry, Physical)

パルス紫外線レーザー照射によって引き起こされるRh$$^{3+}$$イオン錯体のRh$$^{0}$$種への直接光還元反応機構を、分散型X線吸収微細構造(DXAFS)分光法によって調べた。時間分解X線吸収端近傍構造(XANES)には等吸収点がなく、Rh$$^{3+}$$の直接光還元に2種類以上のRh$$^{n+}$$が寄与することを示した。時間分解XANESデータの特異値解析から、直接光還元には3つのRh$$^{n+}$$種が関与することが示唆された。時間分解XANESデータを、交互最小二乗法による多変量解析(MCR-ALS)により解析したところ、3つのRh$$^{n+}$$種の純粋なスペクトルと濃度プロファイルが得られた。Rh$$^{n+}$$種は、3つのXANESスペクトルの特徴から、Rh$$^{3+}$$, Rh$$^{+}$$, Rh$$^{0}$$種に分類できた。得られた濃度プロファイルから、Rhの直接光還元はRh$$^{3+}$$ $$rightarrow$$ Rh$$^{+}$$ $$rightarrow$$ Rh$$^{0}$$の順で進行することが示唆され、Rh$$^{3+}$$とRh$$^{+}$$の光還元、Rh$$^{3+}$$とRh$$^{+}$$の光による自己触媒的還元、Rh$$^{+}$$の光酸化による反応機構により、3種のRh$$^{n+}$$の濃度プロファイルがよく再現できることが示された。

論文

Valence control of charge and orbital frustrated system YbFe$$_{2}$$O$$_{4}$$ with electrochemical Li$$^{+}$$ intercalation

村瀬 知志*; 吉川 裕未*; 藤原 孝将*; 深田 幸正*; 寺西 貴志*; 狩野 旬*; 藤井 達生*; 稲田 康宏*; 片山 真祥*; 吉井 賢資; et al.

Journal of Physics and Chemistry of Solids, 162, p.110468_1 - 110468_6, 2022/03

 被引用回数:0 パーセンタイル:0(Chemistry, Multidisciplinary)

混合原子価系YbFe$$_{2}$$O$$_{4}$$における原子価制御の可能性を検討するため、電荷化学的手法によりLi$$^{+}$$イオンの挿入を試みた。対象物質をLiイオンバッテリー類似のセル状にして実験を行い、Li$$^{+}$$の挿入による格子定数および原子間距離の系統的変化を観測した。イオンの挿入は、電荷量に換算し300mAh/g以上であった。放射光吸収分光による局所構造観測を行ったところ、Li$$^{+}$$はYb層とFe層の間に挿入されることが分かった。本測定からは、金属鉄の微粒子が析出することも示唆された。このため、Li$$^{+}$$の挿入による鉄イオンの原子価の系統的な変化は明瞭に観測されなかった。メスバウア分光法などからは、Li$$^{+}$$は空間的に不均一に挿入されることが示唆されたものの、本研究の結果は、YbFe$$_{2}$$O$$_{4}$$の原子価や物性が電気化学的手法によって制御できる可能性を示すものである。

論文

Activity enhancement of platinum oxygen-reduction electrocatalysts using ion-beam induced defects

木全 哲也*; 垣谷 健太*; 山本 春也*; 下山 巖; 松村 大樹; 岩瀬 彰宏*; Mao, W.*; 小林 知洋*; 八巻 徹也*; 寺井 隆幸*

Physical Review Materials (Internet), 6(3), p.035801_1 - 035801_7, 2022/03

 被引用回数:2 パーセンタイル:0(Materials Science, Multidisciplinary)

High activity is one of the primary requirements for the catalysts in proton exchange membrane fuel cell applications. Previous computational studies suggested that the catalytic activity of Pt nanoparticles could be enhanced by a Pt-carbon (C) support interaction. We have recently found that an enhanced electronic interaction occurs at the interface between an argon-ion (Ar$$^{+}$$)-irradiated glassy carbon (GC) surface and Pt nanoparticles. Here, we report a more than two-fold increase in specific activity (SA) for the Pt nanoparticles on the Ar$$^{+}$$-irradiated GC substrate compared to that on the non-irradiated GC substrate. The mechanism of this activity enhancement was investigated by local structure analysis of the interface. Ar$$^{+}$$ irradiation of the carbon support led to the formation of the Pt-C bonding, thus protecting the deposited Pt nanoparticles from oxidation.

論文

An Automotive intelligent catalyst that contributes to hydrogen safety for the Decommissioning of Fukushima Daiichi Nuclear Power Station (1FD)

田中 裕久*; 正木 清香*; 青谷 拓朗*; 稲川 康平*; 岩田 宗悟*; 相田 樹哉*; 山本 忠亮*; 喜多 知輝*; 大野 瞳*; 竹中 啓恭*; et al.

SAE Technical Paper 2022-01-0534 (Internet), 10 Pages, 2022/03

The catalyst called a Passive Autocatalytic Recombiner (PAR) is required to have robustness that can maintain its activity for more than 30 years in an environment where temperature, humidity, gas concentration, etc. cannot be controlled. Here, it is expected that "An Intelligent Catalyst" for automotive emissions control exhibits excellent performance even in such a harsh environment. The intelligent catalyst is the nanostructure designed perovskite catalyst that has the rejuvenating function instead of preventing aging. The authors emphasize that the technology developed as a catalyst for automobiles is expected to be useful not only in other industries but also as a relief technology from the national crisis.

論文

プルトニウムの体外排出に向けたキレート剤による除染に関する基礎検討; X線吸収分光法によるプルトニウム模擬元素とキレート剤との結合性評価

上原 章寛*; Shuhui, X.*; 佐藤 遼太朗*; 松村 大樹; 辻 卓也; 薬丸 晴子*; 城 鮎美*; 齋藤 寛之*; 田中 泉*; 石原 弘*; et al.

X線分析の進歩,53, p.223 - 229, 2022/03

体内にアクチニドなどの放射性物質が取り込まれると、生体内配位子がアクチニドと化合物を生成し、体内滞留の原因となりうる。本研究では、アクチニドを体外に排出させるためのキレート剤の結合性評価を行うため、キレート剤と結合した元素の局所構造をX線吸収分光法によって解析し結合力を評価した。プルトニウム模擬元素としてジルコニウム(Zr),キレート剤として、EHBP(1-hydroxyethylidene-1,1-diphosphonate)およびDTPA (diethylenetriaminepentaacetate)を用いた。ZrはEHBPと八面体構造の錯体を形成するとともに、Zr-EHBP錯体はZr-DTPA錯体より強い結合を有することが分かった。これらの知見は、放射性元素による内部被ばく線量評価や、放射性元素を体外に取り除くための適切な除染方法の提案につながる。

論文

Bayesian sparse modeling of extended X-ray absorption fine structure to determine interstitial oxygen positions in yttrium oxyhydride epitaxial thin film

熊添 博之*; 五十嵐 康彦*; Iesari, F.*; 清水 亮太*; 小松 遊矢*; 一杉 太郎*; 松村 大樹; 齋藤 寛之*; 岩満 一功*; 岡島 敏浩*; et al.

AIP Advances (Internet), 11(12), p.125013_1 - 125013_5, 2021/12

 被引用回数:1 パーセンタイル:22.97(Nanoscience & Nanotechnology)

This letter presents a Bayesian sparse modeling method to analyze extended X-ray absorption fine structure (EXAFS) data with basis functions built on two-body signals. This method allows us to evaluate regression coefficients proportional to the radial distribution functions of the respective elements and their errors and is very effective for analysis of EXAFS with weak absorption intensity and severe signal-to-noise ratio. As an application example, we used it to analyze EXAFS of an yttrium oxyhydride (YO$$_{x}$$H$$_{y}$$) epitaxial thin film. This EXAFS data shows weak absorption intensity due to the small amount of X-ray absorption in the thin film sample. However, this approach revealed that the radial distance ratio of the second neighbor yttrium to the first neighbor oxygen coincides with that of a tetrahedral configuration. This result demonstrates that the interstitial oxygen position is tetrahedral in the YO$$_{x}$$H$$_{y}$$ thin film.

論文

Distinct variation of electronic states due to annealing in $$T'$$-type La$$_{1.8}$$Eu$$_{0.2}$$CuO$$_{4}$$ and Nd$$_{2}$$CuO$$_{4}$$

浅野 駿*; 石井 賢司*; 松村 大樹; 辻 卓也; 工藤 康太*; 谷口 貴紀*; 齋藤 真*; 春原 稔樹*; 川股 隆行*; 小池 洋二*; et al.

Physical Review B, 104(21), p.214504_1 - 214504_7, 2021/12

 被引用回数:0 パーセンタイル:0(Materials Science, Multidisciplinary)

We performed Cu K-edge X-ray absorption fine-structure measurements on $$T'$$-type La$$_{1.8}$$Eu$$_{0.2}$$CuO$$_{4}$$ (LECO) and Nd$$_{2}$$CuO$$_{4}$$ (NCO) to investigate the variation in the electronic state associated with the emergence of superconductivity due to annealing. The X-ray absorption near-edge structure spectra of as-sintered (AS) LECO are quite similar to those of AS NCO, indicating that the ground state of AS LECO is a Mott insulator. The electron density after annealing $$n_{rm AN}$$ was evaluated for both superconducting LECO and nonsuperconducting NCO and was found to be 0.40 and 0.05 electron per Cu atom, respectively. In LECO but not in NCO, extended X-ray absorption fine-structure analysis revealed a reduction in the strength of the Cu-O bond in the CuO$$_{2}$$ plane due to annealing, which is consistent with the screening effect on phonons in the metallic state. The origin of the difference in doping processes due to annealing is discussed in relation to the size of the charge-transfer gap.

論文

Chromium(VI) adsorption-reduction using a fibrous amidoxime-grafted adsorbent

林 菜月*; 松村 大樹; 保科 宏行*; 植木 悠二*; 辻 卓也; Chen, J.*; 瀬古 典明*

Separation and Purification Technology, 277, p.119536_1 - 119536_8, 2021/12

 被引用回数:5 パーセンタイル:60.29(Engineering, Chemical)

To develop a safe and simple method for the reduction of toxic chromium(VI) to the less harmful chromium(III), we proposed using radiation-induced graft polymerization. This method allows for any functional group to be introduced into conventional polymeric materials. Herein, we synthesized a fibrous adsorbent with amidoxime functional groups that have a high affinity for chromium, and investigated the changes in the chromium valence state over time in the amidoxime-grafted adsorbent. In situ X-ray absorption fine structure analysis revealed that most of the chromium(VI) was reduced to chromium(III) relatively early during the adsorption process, followed by gradual changes in the bonding structure of the amidoxime-chromium complex. It is expected to contribute to the development of practical technologies for wastewater treatment.

論文

Carbonated nanohydroxyapatite from bone waste and its potential as a super adsorbent for removal of toxic ions

関根 由莉奈; 南川 卓也; 山田 鉄兵*; 松村 大樹; 根本 善弘*; 竹口 雅樹*; 杉田 剛; 下山 巖; 香西 直文; 諸岡 聡

Journal of Environmental Chemical Engineering, 9(2), p.105114_1 - 105114_12, 2021/04

 被引用回数:6 パーセンタイル:66.56(Engineering, Environmental)

有害金属除去は安心安全社会構築のために必要な技術である。本研究では、骨の有するイオン交換能を最大限に活用して廃材を用いた有害金属除去材料の開発を行った。炭酸塩水溶液に骨を浸漬することで高炭酸含有ナノアパタイトが形成することを見出した。この材料は、通常の骨、また合成アパタイトに比べて約250、4500倍高いストロンチウム吸着性能を示した。本材料は廃材を利用していることから、低コストかつ高性能な吸着剤として活用が期待できる。

論文

Mechanistic study on the removal of Cs from contaminated soil by rapid ion exchange in subcritical water

福田 達弥*; 高橋 亮*; 原 卓飛*; 尾原 幸治*; 加藤 和男*; 松村 大樹; 稲葉 優介*; 中瀬 正彦*; 竹下 健二*

Journal of Nuclear Science and Technology, 58(4), p.399 - 404, 2021/04

 被引用回数:3 パーセンタイル:51.02(Nuclear Science & Technology)

As a result of the Fukushima nuclear power plant accident in March 2011, massive amounts of soil were contaminated with radioactive Cs. To remediate the contaminated soil, we are developing a desorption technique for removing Cs from soil using subcritical water. We found that rapid ion exchange of Cs with multivalent cations in subcritical water is an effective desorption technique. To understand the mechanism and structural aspects of this process, in situ observations of the soil layer in subcritical water were carried out by high-energy X-ray diffraction together with pair distribution function analysis, and extended X-ray absorption fine structure analysis. Both the desorption experiments and structural studies indicated that conformational changes of the layer containing Cs$$^{+}$$ under subcritical water conditions promoted intercalation of the hydrated Mg and trapped Cs$$^{+}$$, which facilitated a rapid ion-exchange reaction of Mg$$^{2+}$$ and Cs$$^{+}$$.

論文

Local Ir dedimerization followed by ligand-hole hopping in X-ray irradiated thiospinel

平賀 晴弘*; 松村 大樹; 堀金 和正*; 水木 純一郎*

Journal of Physics and Chemistry of Solids, 150, p.109870_1 - 109870_8, 2021/03

 被引用回数:0 パーセンタイル:0(Chemistry, Multidisciplinary)

The extended X-ray-absorption fine structure of a spinel CuIr$$_{2}$$(S$$_{0.95}$$Se$$_{0.05}$$)$$_{4}$$ powder sample, which has the charge-ordered temperature $$T_{rm{CO}}$$ = 190 K, was determined at the Ir $$L_{3}$$ edge for a wide temperature range. All the local structure parameters on the Ir-Ir bonds signified the second structural change at $$T^{*} sim$$ 70 K. Remarkably, the number of Ir dimers decreased by $$sim$$ 10% below $$T^{*}$$, which indicates partial dedimerization by X-ray irradiation. We also reanalyzed the resistance data of CuIr$$_{2}$$S$$_{4}$$ with the variable-range hopping model by focusing on the density of states. The X-ray-induced decrease in resistance was quantitatively explained as a result of the increase in the density of states, which was attributed to the release of holes from the 10%-dedimerized Ir ions. We suppose that the released holes hop over the ligand chalcogen site.

論文

Coordination number regulation of molybdenum single-atom nanozyme peroxidase-like specificity

Wang, Y.*; Jia, G.*; Cui, X.*; Zhao, X.*; Zhang, Q.*; Gu, L.*; Zheng, L.*; Li, L. H.*; Wu, Q.*; Singh, D. J.*; et al.

Chem, 7(2), p.436 - 449, 2021/02

 被引用回数:84 パーセンタイル:99.79(Chemistry, Multidisciplinary)

Nanozymes are promising alternatives to natural enzymes, but their use remains limited owing to poor specificity. Overcoming this is extremely challenging due to the intrinsic structural complexity of these systems. We report theoretical design and experimental realization of a series of heterogeneous molybdenum single-atom nanozymes (named Mo$$_{rm{SA}}$$-N$$_{x}$$-C), wherein we find that the peroxidase-like specificity is well regulated by the coordination numbers of single Mo sites. The resulting Mo$$_{rm{SA}}$$-N$$_{3}$$-C catalyst shows exclusive peroxidase-like behavior. It achieves this behavior via a homolytic pathway, whereas Mo$$_{rm{SA}}$$-N$$_{2}$$-C and Mo$$_{rm{SA}}$$-N$$_{4}$$-C catalysts have a different heterolytic pathway. The mechanism of this coordination-number-dependent enzymatic specificity is attributed to geometrical structure differences and orientation relationships of the frontier molecular orbitals.

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