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Journal Articles

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

Saeki, Morihisa*; Matsumura, Daiju; Nakanishi, Ryuzo*; Yomogida, Takumi; Tsuji, Takuya; Saito, Hiroyuki*; Oba, Hironori*

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

The reaction mechanism of the direct photoreduction of a Rh$$^{3+}$$ ion complex to a Rh$$^{0}$$ species induced by pulsed ultraviolet laser irradiation was studied using dispersive X-ray absorption fine structure (DXAFS) spectroscopy. The time-resolved X-ray absorption near edge structure (XANES) showed the absence of isosbestic points and suggested that more than two Rh$$^{n+}$$ species contribute toward the direct photoreduction of Rh$$^{3+}$$. Analysis of the time-resolved XANES data by singular value deposition showed that the direct photoreduction involves three Rh$$^{n+}$$ species. Multivariate curve resolution by alternating least-squares analysis (MCR-ALS) of the time-resolved XANES data gave pure spectra and concentration profiles of the three Rh$$^{n+}$$ species. The Rh$$^{n+}$$ species were assigned to Rh$$^{3+}$$, Rh$$^{+}$$, and Rh$$^{0}$$ species based on the features of the pure XANES spectra. The concentration profiles suggested that the direct photoreduction proceeds in the order of Rh$$^{3+}$$ $$rightarrow$$ Rh$$^{+}$$ $$rightarrow$$ Rh$$^{0}$$. A reaction mechanism, which was proposed involving photoreductions of Rh$$^{3+}$$ and Rh$$^{+}$$, photoinduced autocatalytic reductions of Rh$$^{3+}$$ and Rh$$^{+}$$, and photooxidation of Rh$$^{+}$$, well reproduced the concentration profiles of three Rh$$^{n+}$$ species.

Journal Articles

Crystalline fully carboxylated polyacetylene obtained under high pressure as a Li-ion battery anode material

Wang, X.*; Tang, X.*; Zhang, P.*; Wang, Y.*; Gao, D.*; Liu, J.*; Hui, K.*; Wang, Y.*; Dong, X.*; Hattori, Takanori; et al.

Journal of Physical Chemistry Letters (Internet), 12(50), p.12055 - 12061, 2021/12

Substituted polyacetylene is expected to improve the chemical stability, physical properties, and additional functions of the polyacetylene backbones, but its diversity is very limited. Here, by applying external pressure on solid acetylenedicarboxylic acid, we report the first crystalline poly-dicarboxylacetylene with every carbon on the trans-polyacetylene backbone bonded to a carboxyl group, which is very hard to synthesize by traditional methods. This unique structure combines the extremely high content of carbonyl groups and high conductivity of a polyacetylene backbone, which exhibits a high specific capacity and excellent cycling/rate performance as a Li-ion battery (LIB) anode. We present a completely functionalized crystalline polyacetylene and provide a high-pressure solution for the synthesis of polymeric LIB materials and other polymeric materials with a high content of active groups.

Journal Articles

Dynamics of water in a catalyst layer of a fuel cell by quasielastic neutron scattering

Ito, Kanae; Yamada, Takeshi*; Shinohara, Akihiro*; Takata, Shinichi; Kawakita, Yukinobu

Journal of Physical Chemistry C, 125(39), p.21645 - 21652, 2021/10

 Times Cited Count:0

Journal Articles

Electrochemically driven specific alkaline metal cation adsorption on a graphene interface

Yasuda, Satoshi; Tamura, Kazuhisa; Kato, Masaru*; Asaoka, Hidehito; Yagi, Ichizo*

Journal of Physical Chemistry C, 125(40), p.22154 - 22162, 2021/10

Understanding electrochemical behavior of the alkaline metal cation-graphene interface in electrolyte is essential for understanding the fundamental electrochemical interface and development of graphene-based technologies. We report comprehensive analysis of the electrochemical behavior of both alkaline metal cations and graphene using electrochemical surface X-ray diffraction (EC-SXRD) and Raman (EC-Raman) spectroscopic techniques in which the interfacial structure of cations and the charging state and mechanical strain of the graphene can be elucidated. EC-SXRD and cyclic voltammetry demonstrated electrochemically driven specific adsorption and desorption of cations on the graphene surface involved in the dehydration and hydration process. This study provides new insight for understanding fundamental electrochemical behavior of the alkaline metal cation-graphene interface and contributes to the development of carbon-based novel applications.

Journal Articles

Stoichiometry of lanthanide-phosphate complexes at the water surface studied using vibrational sum frequency generation spectroscopy and DFT calculations

Kusaka, Ryoji; Watanabe, Masayuki

Journal of Physical Chemistry B, 125(24), p.6727 - 6731, 2021/06

 Times Cited Count:0 Percentile:0(Chemistry, Physical)

Journal Articles

Kinetic and Fourier transform infrared studies on the thermal decomposition of sodium hydride

Kawaguchi, Munemichi

Journal of Physical Chemistry C, 125(22), p.11813 - 11819, 2021/06

 Times Cited Count:0 Percentile:0(Chemistry, Physical)

Isothermal and constant heating thermogravimetry-differential thermal analysis (TG-DTA) and Fourier transform infrared spectrometer (FTIR) measurements have been performed for pre- and post-fired sodium hydride (NaH) in the temperature range of 500-700 K, respectively. Temperature dependence of NaH thermal decomposition rates obtained by the isothermal TGs showed an inflection point at around 620 K, which was caused by two kinds of hydrogen states (rapid diffusing and immobile hydrogen). In the FTIR spectra for the NaH and sodium (Na), the specific signals were observed at around 873.4, 1010.4, 1049.5 and 1125.7 cm$$^{-1}$$, and the integrated values of FTIR signals for post-fired NaH at below 550K and at above 698 K were comparable to those for pre-fired NaH and Na, respectively. Those for post-fired NaH at 602-667 K were the intermediate values of the pre-fired NaH and Na, which denoted that the Na-Na bonds haven't grown sufficiently and the hydrogen coexisted in metallic Na. In order to predict the practical kinetics of NaH thermal decomposition reaction, we suggested the simple kinetics model which assumed two kinds of rapidly diffusing and immobile hydrogen states. The simulation results revealed the inflection point in temperature dependence of the thermal decomposition rates accordingly because the transition from immobile hydrogen to rapid diffusing hydrogen crosses over at around 620 K.

Journal Articles

Freezable and unfreezable hydration water; Distinct contributions to protein dynamics revealed by neutron scattering

Yamamoto, Naoki*; Kofu, Maiko; Nakajima, Kenji; Nakagawa, Hiroshi; Shibayama, Naoya*

Journal of Physical Chemistry Letters (Internet), 12(8), p.2172 - 2176, 2021/03

 Times Cited Count:0 Percentile:0.01(Chemistry, Physical)

Hydration water plays a crucial role for activating the protein dynamics required for functional expression. Yet, the details are not understood about how hydration water couples with protein dynamics. A temperature hysteresis of the ice formation of hydration water is a key phenomenon to understand which type of hydration water, unfreezable or freezable hydration water, is crucial for the activation of protein dynamics. Using neutron scattering, we observed a temperature-hysteresis phenomenon in the diffraction peaks of the ice of freezable hydration water, whereas protein dynamics did not show any temperature hysteresis. These results show that the protein dynamics is not coupled with freezable hydration water dynamics, and unfreezable hydration water is essential for the activation of protein dynamics.

Journal Articles

Neutron spin-echo studies of the structural relaxation of network liquid ZnCl$$_2$$ at the structure factor primary peak and prepeak

Luo, P.*; Zhai, Y.*; Leao, J. B.*; Kofu, Maiko; Nakajima, Kenji; Faraone, A.*; Zhang, Y.*

Journal of Physical Chemistry Letters (Internet), 12(1), p.392 - 398, 2021/01

 Times Cited Count:1 Percentile:70.6(Chemistry, Physical)

Using neutron spin-echo spectroscopy, we studied the microscopic structural relaxation of a prototypical network ionic liquid ZnCl$$_2$$ at the structure factor primary peak and prepeak. The results show that the relaxation at the primary peak is faster than the prepeak and that the activation energy is $$sim 33$$% higher. A stretched exponential relaxation is observed even at temperatures well-above the melting point $$T_{rm m}$$. Surprisingly, the stretching exponent shows a rapid increase upon cooling, especially at the primary peak, where it changes from a stretched exponential to a simple exponential on approaching the $$T_{rm m}$$. These results suggest that the appearance of glassy dynamics typical of the supercooled state even in the equilibrium liquid state of ZnCl$$_2$$ as well as the difference of activation energy at the two investigated length scales are related to the formation of a network structure on cooling.

Journal Articles

Dynamic observation and theoretical analysis of initial O$$_{2}$$ molecule adsorption on polar and $$m$$-plane surfaces of GaN

Sumiya, Masatomo*; Sumita, Masato*; Asai, Yuya*; Tamura, Ryo*; Uedono, Akira*; Yoshigoe, Akitaka

Journal of Physical Chemistry C, 124(46), p.25282 - 25290, 2020/11

The initial oxidation of different GaN surfaces [the polar Ga-face (+c) and N-face (-c) and the nonpolar (10$$bar{1}$$0) ($$m$$)plane] under O$$_{2}$$ molecular beam irradiation was studied by real-time synchrotron radiation X-ray photoelectron spectroscopy and DFT molecular dynamics calculation. The results predict that triplet O$$_{2}$$ either dissociates or chemisorbs at the bridge position on the +c-surface, while on N-terminated -c-surface the O$$_{0}$$2 molecule only undergoes dissociative chemisorption. On the $$m$$-GaN surface, although the dissociation of O$$_{2}$$ is dominant, the bond length and angle were found to fluctuate from those of O$$_{2}$$ molecules adsorbed on the polar surfaces. The computational model including both the surface spin and polarity of GaN is useful for understanding the interface between GaN and oxide layers in metal-oxide electronic.

Journal Articles

Gas barrier properties of chemical vapor-deposited graphene to oxygen imparted with sub-electronvolt kinetic energy

Ogawa, Shuichi*; Yamaguchi, Hisato*; Holby, E. F.*; Yamada, Takatoshi*; Yoshigoe, Akitaka; Takakuwa, Yuji*

Journal of Physical Chemistry Letters (Internet), 11(21), p.9159 - 9164, 2020/11

 Times Cited Count:2 Percentile:42.52(Chemistry, Physical)

Atomically thin layers of graphene have been proposed to protect surfaces through the direct blocking of corrosion reactants such as oxygen with low added weight. The long term efficacy of such an approach, however, is unclear due to the long-term desired protection of decades and the presence of defects in as-synthesized materials. Here, we demonstrate catalytic permeation of oxygen molecules through previously-described impermeable graphene by imparting sub-eV kinetic energy to molecules. These molecules represent a small fraction of a thermal distribution thus this exposure serves as an accelerated stress test for understanding decades-long exposures. The permeation rate of the energized molecules increased 2 orders of magnitude compared to their non-energized counterpart. Graphene maintained its relative impermeability to non-energized oxygen molecules even after the permeation of energized molecules indicating that the process is non-destructive and a fundamental property of the exposed material.

Journal Articles

Nanoscale relaxation in "Water-in-Salt" and "Water-in-Bisalt" electrolytes

Gonzal$'e$z, M. A.*; Borodin, O.*; Kofu, Maiko; Shibata, Kaoru; Yamada, Takeshi*; Yamamuro, Osamu*; Xu, K.*; Price, D. L.*; Saboungi, M.-L.*

Journal of Physical Chemistry Letters (Internet), 11(17), p.7279 - 7284, 2020/09

 Times Cited Count:6 Percentile:81.96(Chemistry, Physical)

Journal Articles

Unusual redox behavior of ruthenocene confined in the micropores of activated carbon

Itoi, Hiroyuki*; Ninomiya, Takeru*; Hasegawa, Hideyuki*; Maki, Shintaro*; Sakakibara, Akihiro*; Suzuki, Ryutaro*; Kasai, Yuto*; Iwata, Hiroyuki*; Matsumura, Daiju; Owada, Mao*; et al.

Journal of Physical Chemistry C, 124(28), p.15205 - 15215, 2020/07

 Times Cited Count:4 Percentile:61.86(Chemistry, Physical)

Journal Articles

Segmental motions of proteins under non-native states evaluated using quasielastic neutron scattering

Fujiwara, Satoru*; Matsuo, Tatsuhito*; Sugimoto, Yasunobu*; Shibata, Kaoru

Journal of Physical Chemistry Letters (Internet), 10(23), p.7505 - 7509, 2019/12

 Times Cited Count:0 Percentile:0.01(Chemistry, Physical)

Characterization of the dynamics of disordered polypeptide chains is required to elucidate the behavior of intrinsically disordered proteins and proteins under non-native states related to the folding process. Here we develop a method using quasielastic neutron scattering, combined with small-angle X-ray scattering and dynamic light scattering, to evaluate segmental motions of proteins as well as diffusion of the entire molecules and local side-chain motions. We apply this method to RNase A under the unfolded and molten-globule (MG) states. The diffusion coefficients arising from the segmental motions are evaluated and found to be different between the unfolded and MG states. The values obtained here are consistent with those obtained using the fluorescence-based techniques. These results demonstrate not only feasibility of this method but also usefulness to characterize the behavior of proteins under various disordered states.

Journal Articles

Impact of stoichiometry on the mechanism and kinetics of oxidative dissolution of UO$$_{2}$$ induced by H$$_{2}$$O$$_{2}$$ and $$gamma$$-irradiation

Kumagai, Yuta; Fidalgo, A. B.*; Jonsson, M.*

Journal of Physical Chemistry C, 123(15), p.9919 - 9925, 2019/04

 Times Cited Count:8 Percentile:50.98(Chemistry, Physical)

Radiation-induced oxidative dissolution of uranium dioxide (UO$$_{2}$$) is one of the most important chemical processes of U driven by redox reactions. We have examined the effect of UO$$_{2}$$ stoichiometry on the oxidative dissolution of UO$$_{2}$$ induced by hydrogen peroxide (H$$_{2}$$O$$_{2}$$) and $$gamma$$-ray irradiation. By comparing the reaction kinetics of H$$_{2}$$O$$_{2}$$ between stoichiometric UO$$_{2.0}$$ and hyper-stoichiometric UO$$_{2.3}$$, we observed a significant difference in reaction speed and U dissolution kinetics. The stoichiometric UO$$_{2.0}$$ reacted with H$$_{2}$$O$$_{2}$$ much faster than the hyper-stoichiometric UO$$_{2.3}$$. The U dissolution from UO$$_{2.0}$$ was initially much lower than that from UO$$_{2.3}$$, but gradually increased as the oxidation by H$$_{2}$$O$$_{2}$$ proceeded. The $$gamma$$-ray irradiation induced the U dissolution that is analogous to the kinetics by the exposure to a low concentration (0.2 mM) of H$$_{2}$$O$$_{2}$$. The exposure to higher H$$_{2}$$O$$_{2}$$ concentrations caused lower U dissolution and resulted in deviation from the U dissolution behavior by $$gamma$$-ray irradiation.

Journal Articles

Development of the ReaxFF methodology for electrolyte-water systems

Fedkin, M. V.*; Shin, Y. K.*; Dasgupta, N.*; Yeon, J.*; Zhang, W.*; van Duin, D.*; Van Duin, A. C. T.*; Mori, Kento*; Fujiwara, Atsushi*; Machida, Masahiko; et al.

Journal of Physical Chemistry A, 123(10), p.2125 - 2141, 2019/03

 Times Cited Count:15 Percentile:89.91(Chemistry, Physical)

no abstracts in English

Journal Articles

Understanding competition of polyalcohol dehydration reactions in hot water

Chang, Y. L.*; Sasaki, Takehiko*; Ribas-Ari$~n$o, J.*; Machida, Masahiko; Shiga, Motoyuki

Journal of Physical Chemistry B, 123(7), p.1662 - 1671, 2019/02

 Times Cited Count:2 Percentile:12.44(Chemistry, Physical)

Dehydration of biomass-derived polyalcohols has recently drawn attention in green chemistry as a prototype of selective reactions controllable in hot water or hot carbonated water, without any use of organic solvents or metal catalysts. Here, we report a free-energy analysis based on first-principles metadynamics and blue-moon ensemble simulations to understand the mechanism of competing intramolecular dehydration reactions of 1,2,5-pentanetriol in hot acidic water. The simulations consistently predict that the most dominant mechanism is the proton-assisted S$$_{rm N}$$2 process, where the protonation of the hydroxyl group by water and the C-O bond breaking and formation occur in a single step. The detailed mechanism found from the simulations shows how the reaction paths are selective in hot water and why the reaction rates are accelerated in acidic environments, thus giving a clear explanation of experimental findings for a broad class of competing dehydration processes of polyalcohols.

Journal Articles

In Situ Time-Resolved XAFS Studies on Laser-induced Particle Formation of Palladium Metal in an Aqueous/EtOH solution

Saeki, Morihisa*; Matsumura, Daiju; Yomogida, Takumi; Taguchi, Tomitsugu*; Tsuji, Takuya; Saito, Hiroyuki*; Oba, Hironori*

Journal of Physical Chemistry C, 123(1), p.817 - 824, 2019/01

 Times Cited Count:6 Percentile:37.24(Chemistry, Physical)

Reaction kinetics of laser-induced particle formation in an aqueous solution of PdCl$$_{4}$$$$^{2-}$$ was investigated by transmission electron microscope (TEM) and dispersive X-ray absorption fine structure (DXAFS). The Pd particle was generated by irradiation of nanosecond pulsed 266-nm laser. The TEM observation showed dependence of the particle size on the laser fluence and promotion of the particle growth by irradiation of high-fluence laser. The DXAFS data give us the Pd$$^{2+}$$ concentration. Temporal changes of the Pd$$^{2+}$$ concentration analyzed based on Finke-Watzky two step mechanism. The analysis elucidates that the laser photon contributes to the reduction of the PdCl$$_{4}$$$$^{2-}$$ ion by the one-photon process and to the autocatalytic growth of the Pd particles by the multi-photon process.

Journal Articles

New insights into the Cs adsorption on montmorillonite clay from $$^{133}$$Cs solid-state NMR and density functional theory calculations

Okubo, Takahiro*; Okamoto, Takuya*; Kawamura, Katsuyuki*; Gu$'e$gan, R.*; Deguchi, Kenzo*; Oki, Shinobu*; Shimizu, Tadashi*; Tachi, Yukio; Iwadate, Yasuhiko*

Journal of Physical Chemistry A, 122(48), p.9326 - 9337, 2018/12

 Times Cited Count:6 Percentile:45.29(Chemistry, Physical)

The structures of Cs adsorption on montmorillonite were investigated by the nuclear magnetic resonance (NMR) spectroscopy. The NMR spectra of Cs adsorbed on montmorillonite samples were measured under different Cs contents and relative humidity levels. NMR parameters were evaluated by the first principle calculations in order to identify the relationship between adsorbed Cs structures and NMR parameters. The comparisons between experimental and theoretical NMR spectra revealed that Cs is preferentially adsorbed at sites near Al for low Cs substituted montmorillonites, and that non-hydrated Cs present in partially Cs substituted samples, even after being hydrated under high relative humidity.

Journal Articles

Finding free-energy landmarks of chemical reactions

Shiga, Motoyuki; Tuckerman, M. E.*

Journal of Physical Chemistry Letters (Internet), 9(21), p.6207 - 6214, 2018/11

 Times Cited Count:4 Percentile:30.21(Chemistry, Physical)

Predicting reaction pathways is one of the most important goals in theoretical and computational chemistry. In this paper, we propose a novel approach to search for free-energy landmarks, i.e., minima and the saddle points, of chemical reactions in an automated manner using a combination of steepest descent and gentlest ascent methods. As demonstrations, we present applications to the ring-opening reaction of benzocyclobutene and an SN2 reaction in aqueous solution.

Journal Articles

Preliminary evaluation of local structure and speciation of lanthanoids in aqueous solution, iron hydroxide, manganese dioxide, and calcite using the L$$_{3}$$-Edge X-ray absorption near edge structure spectra

Ota, Atsuyuki*; Tanaka, Kazuya; Tsuno, Hiroshi*

Journal of Physical Chemistry A, 122(41), p.8152 - 8161, 2018/10

 Times Cited Count:1 Percentile:5.88(Chemistry, Physical)

We investigated the application of L$$_{3}$$-edge XANES spectra to the local structural analysis of lanthanoids in aqueous solution, iron hydroxide, manganese dioxide, and calcium carbonate. For each lanthanoid, the full width at half maximum (FWHM) values of lanthanoid compounds roughly decreased with increasing coordination numbers. However, they did not strictly reflect the local coordination sphere of the lanthanoid complex, but were rather sensitive to their chemical forms. The relationship between the magnitude of the FWHM values was determined by the crystal field splitting or degeneracy of 5d orbitals. The systematic variation of FWHM can be explained by the ligand strength of the ligand molecules (-H$$_{2}$$O$$^{0}$$, -O$$^{-}$$, -OH$$^{-}$$, -CO$$_{3}$$$$^{2-}$$, -Cl$$^{-}$$, and -O$$^{2-}$$) that cause the crystal field splitting. Therefore, the FWHM values of L$$_{3}$$-edge XANES of lanthanoid compounds may be more useful in speciation analysis rather than structural analysis such as EXAFS.

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