研究者詳細 - 村上　直也

論文 - 村上　直也

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Cyclic time-separated redox reaction using accumulated electrons in titanium(iv) oxide in a two-phase system 査読有り国際誌

Suenaga M., Murakami N.

Catalysis Science and Technology 14 ( 3 ) 624 - 629 2023年12月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

A time-separated redox reaction using accumulated electrons in titanium(iv) oxide (TiO2) was cyclically repeated in order to increase the amount of the reduction product that has been limited by the saturation value of accumulated electrons in TiO2. Repetition of the reaction was carried out by utilizing an organic/aqueous two-phase system and the insolubility of substrates and target products in the aqueous phase. The reaction proceeded by repeating two steps: (1) electron accumulation in TiO2 at the bottom of the aqueous phase was induced under ultraviolet irradiation with low-speed stirring and (2) reduction by accumulated electrons in the two-phase interface was performed in the dark with high-speed stirring. Results indicated that the amount of the product monotonically increased as a function of the number of repetition cycles. The relationship of the product amount with the physical and chemical properties of TiO2 is discussed.

DOI： 10.1039/d3cy01645e

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Electron Trap Analysis of Tin(II) Niobate Photocatalyst Particles Using Photoacoustic Infrared Spectroscopy 査読有り国際誌

Tatsuki Shinoda, Toshio Hayashi, Yuichi Yamaguchi, Akihiko Kudo, Naoya Murakami

The Journal of Physical Chemistry C 127 ( 28 ) 13706 - 13711 2023年07月

Photoacoustic Spectroscopic Analysis of Electron-Trapping Sites in Titanium(IV) Oxide Photocatalyst Powder Treated by Ball Milling 査読有り国際誌

Shinoda T., Yamaguchi Y., Kudo A., Murakami N.

Journal of Physical Chemistry C 126 ( 49 ) 20975 - 20982 2022年12月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Photoabsorption of trapped electrons in rutile titanium(IV) oxide (TiO2) before and after ball-milling and annealing treatments was investigated in a wide range of light wavelengths from visible to mid-infrared (IR) regions using photoacoustic spectroscopy (PAS). In the presence of an electron donor under an inert gas atmosphere, photoacoustic signals for all of the samples were increased by ultraviolet irradiation, resulting in the appearance of broad absorption due to electron accumulation in TiO2. For ball-milled TiO2with a large specific surface area (34 m2g-1), mid-IR absorption attributed to free electrons and shallowly trapped electrons was smaller than that of the pristine sample with a small specific surface area (2.8 m2g-1), but broad absorption ascribed to deeply trapped electrons dramatically increased in the range of near-IR to visible regions. This near-IR-visible absorption was slightly observed even in the presence of oxygen, and it was divided into two parts: one was characteristic near-IR absorption of rutile TiO2having a peak at ∼1.0 eV below the bottom of the conduction band, while the other was ball-milling-induced absorption with a peak at ∼1.7 eV. By annealing treatment, absorptions of free electrons/shallowly trapped electrons and deeply trapped electrons increased and decreased, respectively, although not as much as in the pristine sample. At that time, the specific surface area also decreased to 18 m2g-1. In the evaluation of photocatalytic activity, pristine TiO2showed the highest activity for hydrogen (H2) evolution from an aqueous solution containing an electron donor, whereas the rates of H2evolution for the ball-milled and subsequently annealed samples were 0.21 and 0.34 times lower than that for the pristine sample. Thus, we found from the results of PAS measurements that the main factor governing the photocatalytic activity is not specific surface area but the presence of deeper-energy electron-trapping sites formed by pulverization with ball milling.

DOI： 10.1021/acs.jpcc.2c07064

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Elucidation of the behavior of oxygen remaining in water molecules after hydrogen atom abstraction in the plasma/liquid (P/L) interfacial reaction: improvement in the selectivity of ammonia synthesis and parallel production of hydrogen gas 査読有り国際誌

Yoshida S., Murakami N., Takatsuji Y., Haruyama T.

Green Chemistry 25 ( 2 ) 579 - 588 2022年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

The plasma/liquid interfacial (P/L) reaction is a non-catalytic reaction conducted at an ambient temperature and pressure. The reaction employs activated (dissociated or excited) nitrogen and abstracted hydrogen from water molecules to form ammonia. Herein we demonstrated that dissociated nitrogen (atomic nitrogen; Natom) promoted ammonia selectivity more efficiently than excited nitrogen molecules in P/L reactions. We investigated the behavior of water-derived oxygen after abstracting a hydrogen atom from a water molecule. We constructed a connecting reactor that directly connects the P/L reaction locus with a titania bead-filled packed-bed dielectric barrier discharge (PbDBD) device that exhibits high Natom generation efficiency. In this reactor, the P/L reaction produced aqueous ammonia with high selectivity and minimal aqueous nitrate ions, which are the typical by-products of the reaction. We also observed that oxygen and hydrogen atoms from water were released into the gas phase to form NO and hydrogen gases. The removal of oxygen as NO gas from the P/L reaction locus significantly improved the ammonia synthesis selectivity of the P/L reaction. Additionally, the ability to generate hydrogen gas during ammonia synthesis in the P/L reaction enables the simultaneous production of ammonia and hydrogen gas.

DOI： 10.1039/d2gc03491c

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Photoacoustic Infrared Analysis of the Reactivity of Electrons Accumulated in Titanium(IV) Oxide Particles Under a Liquid-phase Photocatalytic Condition 査読有り国際誌

Tatsuki Shinoda, Naoya Murakami

Chemistry Letters 52 ( 1 ) 13 - 16 2022年11月

Reduction of nitrate to ammonia using photocatalytically accumulated electrons on titanium(IV) oxide in a time-separated redox reaction 査読有り国際誌

Murakami N., Suenaga M., Deguchi R.

Inorganic Chemistry Communications 141 2022年07月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Reduction of nitrate (NO3−) to ammonia (NH3) was performed by a time-separated redox reaction using photocatalytically accumulated electrons in a titanium(IV) oxide (TiO2) suspension. The time-separated redox reaction uses a two-step reaction under the control of photoexcitation and an electron acceptor: (1) accumulation of electrons in TiO2 powder under photoexcitation and (2) reduction of added NO3− by accumulated electrons in the dark. Color change of TiO2 depending on the degree of electron accumulation was observed during the reaction, and 8-electron reduction of NO3− to NH3 was performed by accumulated electrons. The results of the time-separated redox reaction using 10 kinds of commercial TiO2 powder indicate that the use of a rutile sample with a large number of trivalent titanium species is a key factor for NH3 production.

DOI： 10.1016/j.inoche.2022.109585

Kyutacar

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Fe(III)-Pt(II) oxide-co-sensitized brookite TiO2 nanorods for photocatalytic degradation of acetaldehyde under visible light 査読有り国際誌

Yu Cao, Shi Nee Lou, Sicong Wang, Hui Yang, Qitao Zhang, Chengyin Wang, Naoya Murakami, Teruhisa Ohno

Applied Catalysis A: General 634 118539 2022年03月

Accumulation Process of Photogenerated Electrons in Titanium(IV) Oxide Photocatalyst Particles: Photoacoustic Infrared Spectroscopy Study 査読有り国際誌

Tatsuki Shinoda, Naoya Murakami

Journal of Physical Chemistry C 126 ( 10 ) 4889 - 4898 2022年03月

Drastically Increase in Atomic Nitrogen Production Depending on the Dielectric Constant of Beads Filled in the Discharge Space 査読有り国際誌

Yuto Tsuchida, Naoya Murakami, Tatsuya Sakakura, Yoshiyuki Takatsuji, Tetsuya Haruyama

ACS Omega 6 ( 44 ) 29759 - 29764 2021年10月

Simultaneous Measurements of Photoabsorption and Photoelectrochemical Performance for Thickness Optimization of a Semiconductor Photoelectrode 査読有り

Murakami N., Watanabe R.

ACS Combinatorial Science 22 ( 12 ) 791 - 795 2020年12月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

© We established a system for simultaneous measurements of photoelectrochemical (PEC) reaction and photoabsorption in a semiconductor photoelectrode. This system uses a photoacoustic technique and photoelectrodes with a film-thickness gradient that was prepared by electrophoretic deposition of tungsten(VI) oxide particles while pulling up a substrate. The system enabled high-throughput determination of optimum film thickness, and the results showed that irradiation direction has a significant influence on PEC performance for a photoelectrode with a thick film. Furthermore, the mechanism of enhancement of PEC performance by postnecking treatment was discussed.

DOI： 10.1021/acscombsci.0c00113

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In situ photoacoustic analysis of near-infrared absorption of rhodium-doped strontium titanate photocatalyst powder 査読有り

Shinoda T., Yamaguchi Y., Kudo A., Murakami N.

Chemical Communications 56 ( 91 ) 14255 - 14258 2020年11月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

© The Royal Society of Chemistry. Near-infrared absorption of strontium titanate (SrTiO3) doped with rhodium (Rh) was investigated by photoacoustic (PA) Fourier transform infrared spectroscopy. In the absence of an electron acceptor and the presence of a hole scavenger, the largest absorption change in the Rh valence state from tetravalent to trivalent was observed in Rh-doped SrTiO3 prepared at 1473 K, which showed the highest activity for hydrogen evolution. PA measurements revealed the effective redox cycle mechanism between tetravalent and trivalent Rh ions in Rh-doped SrTiO3.

DOI： 10.1039/d0cc06414a

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Determination of the internal quantum efficiency for photoelectrochemical reaction in a semiconductor photoelectrode by photoacoustic detection 査読有り

Murakami N., Okuzono K.

Chemical Communications 56 ( 40 ) 5417 - 5420 2020年05月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

© The Royal Society of Chemistry 2020. We showed for the first time the validity of photothermal measurement for determination of internal quantum efficiency, which is one of the most fundamental parameters for energy conversion systems. The measurement method using photoacoustic detection in the present study can be applied to a wide variety of samples and measurement conditions.

DOI： 10.1039/d0cc01911a

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Nitrogen Fixation in a Plasma/Liquid Interfacial Reaction and Its Switching between Reduction and Oxidation 査読有り

Sakakura T., Murakami N., Takatsuji Y., Haruyama T.

Journal of Physical Chemistry C 124 ( 17 ) 9401 - 9408 2020年04月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2020 American Chemical Society. There are multiple active species at the interface between the discharged gas phase and the water phase. Activated nitrogen species are generated in the nitrogen plasma gas by dielectric barrier discharge (DBD). The reaction at the interface between the gas phase containing the activated nitrogen species and water phase (P/L reaction) can produce nitrogen-derived compounds (N-compounds) in water. We have already clarified the mechanism of the P/L reaction focusing on highly active atomic nitrogen in a previous study. In this study, we report the mechanism of the P/L reaction by excited but metastable nitrogen molecules. Involving excited nitrogen molecules [N2(A3ςu+)] with a long lifetime, the reaction selectivity of N-compounds was clarified by quantitative analysis. Moreover, the active species in the water phase (H·, HO·, H2O2) of the P/L reaction were measured, and the involvement of the reaction in the generation of N-compounds was confirmed. The findings clarify that each activated nitrogen species reacts differently with H2O. These results suggest that the occurrence of either an oxidation reaction or a reduction reaction can be regulated by controlling the activated nitrogen species.

DOI： 10.1021/acs.jpcc.0c02392

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Development of Plasmonic Photocatalyst by Site-selective Loading of Bimetallic Nanoparticles of Au and Ag on Titanium(IV) Oxide 査読有り

Zheng Z., Murakami N., Liu J., Teng Z., Zhang Q., Cao Y., Cheng H., Ohno T.

ChemCatChem 2020年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Morphology-controlled rutile titanium(IV) oxide (TiO2) and anatase TiO2 were prepared by a hydrothermal method and their surfaces were selectively loaded with Au, Ag and AuAg bimetallic nanoparticles (NPs) by photo-deposition in order to obtain visible-light responsive photocatalysts. With the help of local surface plasmon resonance (LSPR) of noble metal NPs, the photocatalytic activity of noble metal-loaded TiO2 under visible-light irradiation was improved compared to that of bare TiO2. The enhancement of LSPR on the photocatalytic activity of rutile TiO2 was larger than that of anatase TiO2 with optimum amount of Au or AuAg. In addition, the reusability (stability) of AuAg-loaded TiO2 was much better than that of Ag-loaded TiO2. Double-beam photoacoustic results confirmed different trap energy level distribution lead to different electron transfer ways, resulting in different oxidizing capabilities and they gave one of important strategies for designing visible-light responsive TiO2.

DOI： 10.1002/cctc.202000366

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Photoacoustic Fourier Transform Near- and Mid-Infrared Spectroscopy for Measurement of Energy Levels of Electron Trapping Sites in Titanium(IV) Oxide Photocatalyst Powders 査読有り

Shinoda T., Murakami N.

Journal of Physical Chemistry C 123 ( 19 ) 12169 - 12175 2019年05月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2019 American Chemical Society. Electron trapping sites in titanium(IV) oxide photocatalyst powders were investigated by photoacoustic (PA) Fourier transform near-infrared spectroscopy (FT-NIR) and mid-infrared spectroscopy (FT-MIR). PA measurements using FT-NIR and FT-MIR enabled in situ observation of the energy levels of electron trapping sites in wide energy levels (0.1-1.9 eV) below the bottom of the conduction band. During ultraviolet (UV) irradiation, PA intensity increased depending on the wavenumber, and changes in the PA spectra were observed as a result of the trivalent titanium species generated by accumulation of electrons at trapping sites. Moreover, the PA spectral shape during UV irradiation was essentially different between the crystal structures, and it greatly depended on the crystal structure rather than other properties such as specific surface area and particle size. The results for various samples suggest that anatase has shallower energy levels of electron trapping sites than those of rutile and brookite, with the main energy level of the trapping sites being deep in the order of brookite > rutile > anatase. Thus, the PA technique using FT-NIR and FT-MIR is an effective method for measurements of energy levels of electron trapping sites in semiconductor photocatalysts.

DOI： 10.1021/acs.jpcc.9b02876

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Improvement of photocatalytic activity of high specific surface area graphitic carbon nitride by loading a co-catalyst 査読有り

Chen Y., Murakami N., Chen H.Y., Sun J., Zhang Q.T., Wang Z.F., Ohno T., Zhang M.

Rare Metals 38 ( 5 ) 468 - 474 2019年05月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2014, The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg. Graphitic carbon nitride (g-C3N4) was synthesized by heating melamine and was then treated with sodium hydroxide solution under a hydrothermal condition to obtain g-C3N4 with a large specific surface area (HSSA). HSSA shows higher photocatalytic activity for decomposition of acetaldehyde than that of original g-C3N4. HSSA was modified with RuO2 as a co-catalyst by the impregnation method. HSSA loaded with 0.05 wt% RuO2 shows the highest photocatalytic activity for acetaldehyde decomposition under visible light (λ = 455 nm).

DOI： 10.1007/s12598-014-0327-y

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Synthesis of anatase TiO#D2#DR with exposed {001} and {101} facets and photocatalytic activity 査読有り

Sun J., Zhang M., Wang Z.F., Chen H.Y., Chen Y., Murakami N., Ohno T.

Rare Metals 38 ( 4 ) 287 - 291 2019年04月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2014, The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg. Anatase titanium(IV) oxide (TiO2) particles with exposed {001} and {101} facets were prepared by hydrothermal treatment of amorphous TiO2 with H2O2–NH3 solution. Crystal phase, shape, and size of TiO2 particles are found to be greatly dependent on the ratio of H2O2–NH3 solution. The prepared TiO2 particles with specific exposed crystal faces show higher photocatalytic activity for acetaldehyde decomposition than commercial spherical TiO2 particles. This result implies that recombination is prevented by spatial separation of redox sites in the particles because of selective migration of electrons and positive holes to specific exposed crystal faces and/or different reactivity of electrons and positive holes on the specific exposed crystal face.

DOI： 10.1007/s12598-014-0329-9

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Contribution of Discharge Excited Atomic N, N#D2#DR*, and N#D2#DR#U+#UR to a Plasma/Liquid Interfacial Reaction as Suggested by Quantitative Analysis 査読有り

Sakakura T., Murakami N., Takatsuji Y., Morimoto M., Haruyama T.

ChemPhysChem 20 1467 - 1474 2019年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electric-discharge nitrogen comprises three main types of excited nitrogen species-atomic nitrogen (N atom ), excited nitrogen molecules (N 2 *), and nitrogen ions (N 2+ ) – which have different lifetimes and reactivities. In particular, the interfacial reaction locus between the discharged nitrogen and the water phase produces nitrogen compounds such as ammonia and nitrate ions (denoted as N-compounds generically); this is referred to as the plasma/liquid interfacial (P/L) reaction. The N atom amount was analyzed quantitatively to clarify the contribution of N atom to the P/L reaction. We focused on the quantitative relationship between N atom and the produced N-compounds, and found that both N 2 * and N 2+ , which are active species other than N atom , contributed to P/L reaction. The production of N-compounds from N 2 * and N 2+ was enhanced upon UV irradiation of the water phase, but the production of N-compounds from N atom did not increase by UV irradiation. These results revealed that the P/L reactions starting from N atom and those starting from N 2* and N 2+ follow different mechanisms.

DOI： 10.1002/cphc.201900212

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光音響分光法による光触媒反応の解析

村上直也

化学と教育 ( 公益社団法人日本化学会 ) 67 ( 8 ) 342 - 345 2019年01月

担当区分：責任著者記述言語：日本語掲載種別：記事・総説・解説・論説等（学術雑誌）

<p>光音響分光法は，光吸収によって生じた励起種（例えば，励起状態にある電子など）が基底状態に戻る際に放出される熱を，物質の熱膨張によって生じた圧力変化（音波）として検出する手法であり，音の大きさによって光吸収量を評価する。そのため，微粒子の分光測定の際に問題となる光散乱の影響を受けることなく，そのままの状態での測定が可能である。本稿では，光音響分光法の概要と，これを光触媒反応に適用した著者らの取り組みについて紹介する。</p>

DOI： 10.20665/kakyoshi.67.8_342

CiNii Article

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Operando Analysis of Electron Accumulation in Titanium(IV) Oxide Particles in an Aqueous Suspension Using a Photoacoustic Spectroscopic Method 査読有り

Murakami N., Shinoda T.

Journal of Physical Chemistry C 123 ( 1 ) 222 - 226 2018年12月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Copyright © 2018 American Chemical Society. The time course of photoabsorption of an aqueous suspension of titanium(IV) oxide (TiO2) particles was studied using photoacoustic (PA) spectroscopy. In the absence of an electron acceptor and the presence of an electron donor, ultraviolet irradiation increased PA intensity because photoabsorption of the suspension increased due to trivalent titanium (Ti3+) species generated by electron accumulation in TiO2 particles. In contrast, the addition of methylene blue (MB) as an acceptor caused a decrease in PA intensity, indicating that accumulated electrons were consumed by reduction of MB to colorless leuco-MB. The results for various TiO2 particles indicated that Ti3+ density is determined by this method. Moreover, the measurement can be applicable to quantitative operando analysis for accumulated electrons in a photocatalytic reaction. ©

DOI： 10.1021/acs.jpcc.8b10566

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