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■ SANOB・2024 (Full Paper) ETRAPD　 K. Sano, T. Ishida, T. Shimada, H. Tachibana, M. Takashima, B. Ohtani, S. Takagi and H. Inoue, Photocatalytic hydrogen evolution from transparent aqueous dispersion of quantum-sized SnO2 nanoparticles: Effect of electron trap density within one particle, J. Phys. Chem. C, published (2024). [DOI] A facile methodology of preparing a transparent aqueous dispersion of SnO2 (rutile) nanoparticles through sol/gel propagative hydrolysis/condensation of SnCl4 was reported. The transparent aqueous dispersion of SnO2 using wet nanoparticles (wet-NPs) as prepared exhibited an enormous enhancement of the photocatalytic H2 evolution reaction upon UV light irradiation, while NPs once dried from wet-NPs (dry-NPs) afforded only a turbid aqueous dispersion with completely silent reactivity against H2 evolution. Although wet- and dry-NPs of SnO2 have the same quantum-sized crystallites, the striking difference of the reactivity was ascribable to the different sizes of wet-NPs (6 nm) in a monomeric form and dry-NPs (58 nm) as agglomerated clusters in the aqueous dispersion. Detailed analysis of electron trap density by means of reversed double-beam photoacoustic spectroscopy (RDB-PAS) to reveal the energy-resolved distribution of electron traps and conduction-band bottom (ERDT/CBB) pattern indicated that the extremely small number of electron traps within one particle of wet-NPs enabled the enormous enhancement of H2 evolution, while a much larger number of electron traps within clusters of dry-NPs could efficiently capture the carrier electron to undergo dominant charge recombination, leading to being silent against H2 evolution.

■ LIBOR・2024 (Paper) ETRAPD　 M. Kajabova, T. Strysovsky, A. Bikbashev, Z. Kovarova, K. Simkovicova, R. Prucek, A. Panacek, P. Novak, J. Kopp, J. Kaslik, A. Malara, P. Frontera, S. Vajda, B. Ohtani, M. Takashima and L. Kvitek, Defect engineering in heterogeneous catalysis: CO2 hydrogenation on iron-based catalysts, J. CO2 Utilization, 85, 102863 (2024).* [DOI]

■ NATAS・2024 (Article) ETRAPD　 E. Serra-Perez, G. Drazic, M. Takashima, B. Ohtani, G. Zerjav, S. Kovacic and N. Novak Tusar, Influence of the surface structure of the TiO2 support on the properties of the Au/TiO2 photocatalyst for water treatment under visible light, Catal. Today, 437, 114264 (2024).* [DOI] Plasmonic composites combining titanium dioxide (TiO2) with highly dispersed noble metal nanoparticles have attracted great interest as they exhibit improved photocatalytic performance compared to the bare TiO2. In this article, TiO2-Au composite nanorods were synthesised by wet impregnation in combination with calcination. The obtained plasmonic composites were characterized by TEM, SEM, XRD, N2 sorption, UV-Vis diffuse reflectance spectroscopy (UV-Vis DR) and reversed double-beam photoacoustic spectroscopy (RDB-PAS) analysis. The RDB-PAS analysis revealed that the TiO2 nanorods (TNR) contain amorphous areas on the surface that influence the size of the grown gold nanoparticles. The amount of amorphous phase on the TiO2 surface of the analysed TNR samples increases from 16.4 %, 17 % and 20.2 % for TNR-A, TNR-B and TNR-C, respectively, and is closely related to the point of charge(pHPZC), which increases from the 3.9 ± 0.06, 4.7 ± 0.07 and 5.7 ± 0.04 for TNR-A, TNR-B and TNR-C, respectively. Au nanoparticle size distribution analysis obtained on the TNR surface shows that smaller Au nanoparticles are formed with pHPZC increase of the TNR support, i.e. 14.8 nm, 12.5 nm and 11.6 nm for TNR-A, TNR-B and TNR-C, respectively. This confirms that the differences in the surface charge of the TiO2 support influence the extent of hydrolysis of the Au precursor and its subsequent nucleation. Finally, the formation of OH・ radicals was monitored using fluorescence probe method with coumarin as the probe molecule. The results revealed that the TiO2/Au composites are capable of generating OH radicals under visible light illumination, with cat-C, containing the smallest Au particle sizes, being the most active among the materials tested.

■ MT4CT・2024 (Article) ETRAPN　 Q. Xi, V. Papaefthimiou, N. Le Breton, M. Lenertz, M. Takashima, V. Keller, B. Vileno and T. Cottineau*, Influence of Nitridation Conditions on the Doping Sites and Photocatalytic Visible Light Activity of Nb,N-Codoped TiO2, Chem. Mater., published (2024). [DOI] The photocatalytic performance of Nb,N-codoped TiO2 nanoparticles obtained via the sol-gel method was compared to that of N-doped TiO2. The study focused on investigating the effects of nitridation conditions on nitrogen insertion with a highlight on the nature of the doping sites in the photocatalyst depending on the initial presence of niobium in the TiO2. The photodegradation of methylene blue in solution under UV, visible, and simulated solar light was used to evaluate the photocatalytic activity of TiO2, Nb- or N-doped TiO2, and Nb,N-codoped TiO2 nanoparticles. Codoped TiO2 produced by mild thermal nitridation exhibits the best photocatalytic activity, with a strong contribution from visible light. On the contrary, the codoped TiO2 produced by more intense thermal nitridation presents lower photocatalytic performances than TiO2 despite a small improvement of activity in the visible range. In addition to material characterization (X-ray diffraction, UV-vis spectroscopy, and X-ray photoelectron spectroscopy), electron paramagnetic resonance and reversed double-beam photoacoustic spectroscopy measurements were used to identify the respective doping sites and ultimately propose the electronic band structure for each sample of Nb:TiO2, N:TiO2, and Nb,N:TiO2. Proper thermal nitridation conditions improve the charge compensation between Nb5＋ and N3-, thereby enhancing the photocatalytic activity. However, too intense nitridation conditions led to the generation of oxygen vacancies and a large amount of Ti3＋ acting as charge recombination centers, resulting in significant deterioration of the photocatalytic performances. This study highlights the importance of understanding the intricate charge compensation process in codoped (M,N) TiO2 materials, as the photocatalytic performance cannot be elucidated solely by the cation/anion ratio but also by considering the nature of the doping sites generated during synthesis.

■ KAGES・2023 (Full Paper) ETRAPD　 Y. Kageshima*, H. Inuzuka, H. Kumagai, B. Ohtani, K. Teshima and H. Nishikiori*, Photothermal Boosting of Photocatalytic Hydrogen Evolution Induced by Defects and Cocatalysts on TiO2, J. Phys. Chem. C., 127, 18327-18339 (2023).* [DOI]

■ XINTC・2023 (Article) ETRAPD　 F. Yu, C. Wang, R. Wang, Y. Li, B. Ohtani, A. Fujishima, Y. Liu and X. Zhang, Solution Plasma Engineers the Surface of N-TiO2 for Thermal Assisted Photocatalysis, Appl. Surf. Sci., 624, 157119 (2023).* [DOI]

■ SAIME・2023 (Research paper) ETRAPD　 S. Emin, M. Machreki, T. Chouki, G. Tyuliev, D. Zigon, B. Ohtani, A. Loukanov and P. Stefanov, Defective TiO2 Nanotube Arrays for Efficient Photoelectrochemical Degradation of Organic Pollutants, ACS Omega, 8, 21605-21617 (2023).* [DOI]

■ SNFEN・2023 (Article) ETRAPD　 M. Preeyanghaa, C. Chuaicham, B. Vellaichamy, S. Shenoy, W. Li, K. Manokaran, E. Varathan, B. Neppolian, B. Ohtani, K. Sasaki and K. Sekar, Unveiling the influence of Fe2O3 nanoparticles on CuxO-TiO2(B) nanofiber for dual Z-scheme electron transfer visible light photocatalysts: investigation on local atomic structures and electronic properties, Environ. Sci. Nano, 10, 1268-1283 (2023).* [DOI]

■ SNGCS・2023 (Article) ETRAPD　 K. Sasaki, T. Inoue, C. Chuaicham, N. Saito and B. Ohtani, Z-scheme heterojunction of graphitic carbon nitride and calcium ferrite in converter slag for the photocatalytic imidacloprid degradation and hydrogen evolution, J. Photochem. Photobiol. A Chem., 440, 114644 (2023).* [DOI]

■ SZYMO・2023 (Article) ETRAPD　 S. Dudziak, E. Kowalska, K. Wang, J. Karczewski, B. Ohtani and A. Zielinska-Jurek, The interplay between dopant and a surface structure of the photocatalyst - the case study of Nb-doped faceted TiO2, Appl. Catal. B. Environ., 328, 122448 (2023).* [DOI]

■ MAMAT・2023 (Short Communication) ETRAPD　 M. Musa, M. H. b. Mamat, N. Vasimalai, M. Malek, M. Ahmad, A. Suriani, A. Mohamed, H. Hassan, A. Subki, B. Ohtani and M. Rusop, Formation of a Novel Nanorod-Assembled TiO2 Actinomorphic-Flower-Like-Microsphere Film via Ta doping using a Facile Solution Immersion Method, Nanomaterials, 13, 256 (2023).* [DOI] A novel tantalum (Ta)-doped titanium dioxide with unique nanorod-assembled actinomorphic-flower-like-microsphere structured film (TTD) has been fabricated via the solution immersion method in a Schott bottle with improvised clamp. The samples were characterised using FESEM, HRTEM, XRD, Raman, and Hall effect measurements for their structural and electrical properties. Compared to the undoped sample, the rutile-phased TTD sample has higher electron concentration and mobility, and finer nanorods with an average diameter of 100nm that assembled to form microsphere-like structures. In addition, a reversed double-beam photoacoustic spectroscopy measurement has been performed for TTD which reveals that the sample has a high electron trap density up to 2.5μmolg -1 . The TTD showed promising results when employed as the sensing material for a resistive-type humidity sensor with the highest sensitivity of 310 obtained at 3 at.% Ta doping.

■ TKCNO・2022 (full paper) ETRAPD　 T. Khedr, S. M. El-Sheikh, M. Endo-Kimura, K. Wang, B. Ohtani and E. Kowalska, Development of sulfur-doped graphitic carbon nitride for hydrogen evolution under visible light irradiation, Nanomaterials, 13, 62 (2022).* [DOI]

■ BLACK・2022 (Article) ETRAPD　 M. Janczarek*, M. Endo-Kimura, K. Wang, Z. Wei, M. A. Akanda, A. Markowska-Szczupak, B. Ohtani and E. Kowalska*, Is black titania a promising photocatalyst?, Catalysts, 12, 1320 (2022).* [DOI]

■ XINTB・2022 (Research Article) ETRAPD　 R. Wang, G. Che, C. Wang, C. Liu, B. Liu, B. Ohtani, Y. Liu and X. Zhang, Alcohol plasma processed surface amorphization for highly efficient photocatalysis, ACS Catal., 12, 12206-12216 (2022).* [DOI]

■ SNFET・2022 (article) ETRAPD　 L. Zhang, C. Chuaicham, V. Balakumar, K. Sekar, B. Ohtani and K. Sasaki, Determination of the roles of FeIII in the interface between titanium dioxide and montmorillonite in FeIII-doped montmorillonite/titanium dioxide composites as photocatalysts, Appl. Clay Sci., 227, 106577 (2022).* [DOI]

■ CSOKC・2022 (Report) ETRAPD　 L. Csoka, W. Hosakun, O. Kolonics and B. Ohtani, Reversed double-beam photoacoustic spectroscopic analysis of photoinduced change in absorption of cellulose fibres, Sci. Rep., 12, 12475 (2022).* [DOI] [LINK]

■ SNGBI・2022 (Article) ETRAPD　 C. Chuaicham, K. Sekar, B. Vellaichamy, J. Uchida, T. Katsurao, H. Sakabe, B. Ohtani and K. Sasaki*, Efficient photocatalytic degradation of emerging ciprofloxacin under visible light irradiation using BiOBr/carbon quantum dot/saponite composite, Environ. Res., 113635 (2022).* [DOI] The use of visible-driven photocatalysts has fascinated attention as a capable and sustainable approach for wastewater remediation. In this work, BiOBr/carbon quantum dot (CQDs)/saponite composites (CQDs/Clay@BiOBr) were fabricated via hydrothermally using two different CQDs/Clay precursors (in-situ synthesis (IS) and physical mixing (PM)). The obtained products were characterized, and the photocatalytic performances of the prepared samples were evaluated in the photocatalytic decomposition of emerging ciprofloxacin (CIP) pharmaceutical waste. The highest CIP mineralization performance was achieved when a combination of BiOBr and CQDs/Clay (IS) with the appropriate proportion because the strong adhesion between CQDs and clay generate a great heterojunction in the composite. The stronger interaction of CQDs and better distribution of CQDs on the surface of clay in the CQDs/Clay (IS) enhanced the interaction of BiOBr and CQDs, and avoided the re-agglomeration of excess of CQDs on surface of BiOBr which reduce the active surface to receive the light and react with CIP. The ultrafast degradation rate of the optimized CQDs/Clay@BiOBr composite was better compared to others. The significant improvement in the CIP degradation efficiency of the CQDs/Clay@BiOBr composite was attributed to the excellent separation and transportation of photogenerated electrons and holes, as confirmed by photoluminescence, photocurrent density, and electrochemical impedance spectroscopy results. Moreover, the photocatalytic degradation mechanism of CIP in the CQDs/Clay@BiOBr composite was proposed based on the electronic states of each material in the composite and on a scavenger test. Thus, the proposed CQDs/Clay@BiOBr composite can be employed as a potential visible-light-driven photocatalyst for the decomposition of organic contaminants in wastewater.

■ ZESPC・2022 (特集) ETRAPR　 大谷文章，光触媒の構造−活性相関解析の課題と展望，Electrochemistry，90，107-114（2022）* [DOI]

■ TKBWO・2022 (Review) ETRAPR　 T. Khedr, K. Wang, D. Kowalski, S. M. El-Sheikh, H. M. Abdeldayem, B. Ohtani and E. Kowalska, Bi2WO6‐based Z-scheme photocatalysts: Principles, mechanisms and photocatalytic applications, Chem. Eng. J., 10, 107838 (2022).* [DOI]

■ ZCCVO・2022 (フォーラム（会員の声）) ETRAPR　 大谷文章，現地・対面信仰をのりこえろ！，触媒，64，130-131（2022） [LINK]

■ NUTCN・2022 (Original Research Article) ETRAPD　 P. Sakuna, P. Ketwong, B. Ohtani, J. Trakulmututa, T. Kobkeatthawin and S. M. Smith, Surface and Bulk Structures of Metal Doped and Co-doped Graphitic Carbon Nitride Particles Influences on Acetic Acid Photooxidation, Front. Chem., 10, 825786 (2022).* [DOI]

■ SNETS・2022 (Research Paper) ETRAPD　 C. Chuaicham, K. Sekar, V. Balakumar, Y. Mittraphab, K. Shimizu, B. Ohtani and K. Sasaki, Fabrication of graphitic carbon nitride/ZnTi-mixed metal oxide heterostructure: Robust photocatalytic decomposition of ciprofloxacin, J. Alloy Comp., 906, 164294 (2022).* [DOI] Photocatalytic treatment is a remarkable process that is popular for the degradation of several organic contaminants in wastewater. In this work, a series of graphitic carbon nitride/ZnTi-mixed metal oxide (CN/ ZnTi-MMO) composites were prepared as photocatalysts through simple calcination. The CN-MMO samples were characterized and applied for photocatalytic degradation of ciprofloxacin (CIP), which is an antibiotic model pollutant. The optimized CN/ZnTi-MMO composite showed complete degradation of CIP within 20 min, leading to a rate constant that is approximately 6 times that of pristine CN and 7 times that of ZnTi- MMO. The increase in the degradation rate of the optimized CN/ZnTi-MMO composite was attributed to the excellent separation and transportation of photogenerated electron-holes pairs, as proven by the photo-luminescence, photocurrent density, and electrochemical impedance spectroscopy results. Moreover, the energy-resolved distribution of the electron trap (ERDT) pattern of the composite sample suggests the formation of an interfacial electron trap state due to interfacial contraction in the composite, resulting in the excited electrons being trapped and avoiding charge recombination. Based on the optical properties, ERDT results, and activity test, a photocatalytic degradation mechanism of CIP over a CN/ZnTi-MMO composite was proposed. Additionally, the degraded solution showed less bio-toxicity than the original CIP solution. Thus, the CN/ZnTi-MMO composite can be employed as a potential visible-light-driven photo-catalyst for the detoxification of pharmaceutical wastewater.

■ ZSPPC・2022 (講座［1］) ETRAPR　 大谷文章，逆二重励起光音響分光法による光機能材料の同定と解析，分光研究，71，28-35（2022）* [LINK]

■ AKSOT・2022 (full paper) ETRAPD　 R. Kojima, B. Ohtani and H. Tada*, Photocatalytic Activity of Radial Rutile Titanium(IV) Oxide Microspheres for Aerobic Oxidation of Organics, ChemPhysChem, 23, e202100793 (2022).* [DOI]

■ SNZNC・2022 (Article) ETRAPD　 C. Chuaicham, T. Inoue, V. Balakumar, Q. Tian, B. Ohtani and K. Sasaki, Visible light-driven ZnCr double layer oxide photocatalyst composites with fly ashes for the degradation of ciprofloxacin, J. Environ. Chem. Eng., 10, 106970 (2022).* [DOI]

■ SNFEM・2021 (full paper) ETRAPD　 L. Zhang, C. Chuaicham, V. Balakumar, B. Ohtani and K. Sasaki*, Fabrication of adsorbed Fe(III) and structurally doped Fe(III) in montmorillonite/TiO2 composite for photocatalytic degradation of phenol, Minerals, 11, 1381 (2021).* [DOI] [LINK]

■ ILTIO・2021 (Full Paper) ETRAPD　 J. Luczak, A. Pancielejko, G. Chen, M. Takashima, A. Zaleska-Medynska* and B. Ohtani, How do ionic liquids affect the surface structure of titania photocatalyst? An Electron Trap Distribution-analysis Study, J. Phys. Chem. C, 125, 28143-28149 (2021).* [DOI] Titanium(IV) oxide, titania, photocatalyst particles were prepared from titanium alkoxide in the presence of several kinds of ionic liquids, and it was clarified that a group of samples exhibited photocatalytic activity for phenol degradation under the irradiation of light of wavelength >400 nm higher than those of the other group of samples. Although the conventional structural analytical results could not be related to the activity, electron-trap distribution measured by reversed double-beam photoacoustic spectroscopy suggested that a part of the ionic liquid induced the creation of a surface amorphous layer covered with hydrophobic organic residues to enhance the adsorption of phenol on the surface.

■ PPCST・2022 (Perspective) ETRAPR　 B. Ohtani and M. Takashima, Happy Photocatalysts and Unhappy Photocatalysts: Electron Trap-distribution Analysis for Metal Oxide-sample Identification, Catal. Sci. Technol., 12, 354-359 (2022).* [DOI] [LINK] A strange story, including a new concept of identification of inorganic solid materials and of photocatalyst design, is told here. Why is it that solid materials have not been identified, while organic chemists are required to identify their organic compounds for publication of a report? What is the meaning of identification? Why is it almost impossible to identify inorganic solids? Is it possible to identify an inorganic solid by using a certain fingerprint? Can energy-resolved distribution of electron traps (ERDT) patterns be fingerprint of solid materials? What do ERDT/CBB (conduction-band bottom) patterns tell us about the photocatalytic activity of titania samples?

■ INVEG・2021 (Research Article) ETRAPD　 I. Velo-Gala, A. Torres-Pinto, C. G. Silva, B. Ohtani, A. M. Silva and J. L. Faria, Graphitic carbon nitride photocatalysis: the hydroperoxyl radical role revealed by kinetic modelling, Catal. Sci. Tech., 11, 7712-7726 (2021).* [DOI]

■ SNGSS・2021 (Full Paper) ETRAPD　 C. Chuaicham, K. Sekar, Y. Xiong, V. Balakumar, Y. Mittraphab, K. Shimizu, B. Ohtani, I. Dabo and K. Sasaki, Single-step synthesis of oxygen-doped hollow porous graphitic carbon nitride using polyoxyethylene stearyl ether for the photocatalytic degradation of ciprofloxacin, Chem. Eng. J., 425, 130502 (2021).* [DOI]

■ IDEHY・2021 (Full Paper) ETRAPD　 E. Doustkhah, M. H. Assadi, K. Komaguchi, N. Tsunoji, M. Esmat, N. Fukata, O. Tomita, R. Abe, B. Ohtani and Y. Ide*, In Situ Blue Titania via Band Shape Engineering for Exceptional Solar H2 Production in Rutile TiO2, Appl. Catal. B. Environ., 297, 120380 (2021).* [DOI]

■ SNGCR・2021 (Full paper) ETRAPD　 C. Chuaicham*, Y. Xiong, K. Sekar, W. Chen, L. Zhang, B. Ohtani, I. Dabo and K. Sasaki*, A promising Zn-Ti layered double hydroxide/Fe-bearing montmorillonite composite as an efficient Z-scheme photocatalyst for Cr(VI) reduction: Insight into the role of Fe impurity in montmorillonite, Appl. Surf. Sci., 546, 148835 (2021).* [DOI]

■ SNGCU・2021 (Full Paper) ETRAPD　 S. Karthikeyan*, C. Chuaicham, B. Vellaisamy, W. Li, B. Ohtani and K. Sasaki*, Cubic Cu2O nanoparticles decorated on TiO2 nanofiber heterostructure as an excellent synergistic photocatalyst for H2 production and sulfamethoxazole degradation, Appl. Catal. B: Environ., 294, 120221 (2021).* [DOI] We report a simple strategy for providing a homogenous TiO2 nanofibre host environment to stabilize Cu2O nanoparticles with an average size of ~60 nm and high dispersibility. We found that the small fraction of Cu2O nanoparticles in direct contact with TiO2 nanofibre arrays (diameter ~300 nm and length ~651 nm) showed excellent synergistic Cu2O/TiO2-NF photocatalyst for H2 production rate of 48 μmol.g-1.h-1 with an apparent quantum efficiency of 3.6%. The significant H2 production rate was much higher (factor of ~6.5 times) compared with unmodified TiO2-NF. In addition, the synergistic Cu2O/TiO2-NF photocatalyst showed significant sulfamethoxazole oxidative-degradation (7×10-2mmol.g-1.min-1) within 10 min and was highly stable during five cycles. The small fraction of Cu2O nanoparticles are well dispersed and form heterojunction to promote charge transfer and provide active sites. This argument is verified by morphology characterisation, band alignment, energy-resolved distribution of electron traps, electrochemical transient photocurrent, and electrochemical impedance (EIS).

■ BRRUL・2021 (Letter) ETRAPD　 G. Chen, M. Takashima* and B. Ohtani, Direct amorphous-structure analysis: How are surface/bulk structure and activity of titania photocatalyst particles changed by milling?, Chem. Lett., 50, 644-648 (2021).* [DOI] ●乳鉢中の磨砕と焼成をおこなったルチル酸化チタンサンプルについて逆二重励起光音響分光法によって得られたERDT/CBBパターンをもとにして構造解析をおこない，磨砕/焼成によってすくなくとも3種類のアモルファス相を特定して定量できることをしめした． Changes in surface and bulk structures of rutile titania particles induced by braying up to 10 d and post calcination in air at 773 K were analyzed by reversed double-beam photoacoustic spectroscopy. The observed energy-resolved distribution of electron traps indicated that the surface was amorphized by braying to give rutile-core amorphous-shell structure and the amorphous layer was partly recrystallized by post-calcination leaving grain boundaries in the surface layers, both of which may cause the observed markedly decreased photocatalytic activities.

■ HANGB・2021 (Full Paper) ETRAPD　 H. Sudrajat*, M. Kitta, R. Ito, S. Nagai, T. Yoshida, R. Katoh, B. Ohtani, N. Ichikuni and H. Onishi, The Role of the Shell in Core-Shell-Structured La-Doped NaTaO3 Photocatalysts, Phys. Chem. Chem. Phys., 23, 8868-8879 (2021).* [DOI] Understanding the science behind highly active materials is essential for advancement in the field of photocatalytic water splitting for solar energy harvesting. Sodium tantalate (NaTaO3) doped with La cations is one of the best engineered materials for efficient water splitting to evolve hydrogen. In this study, physical insights into the sensitivity of the water-splitting activity to the spatial La distribution are discussed. The spatial distribution of La cations placed at the Na site was found to dictate the energy gradient of the conduction band bottom (CBB), resulting in a tunable electron population and hence water-splitting activity. A less homogeneous sample with a sufficiently large CBB gradient exhibited higher water-splitting activity. The mechanism of gradient tuning of the CBB through controlling the spatial dopant distribution is expected to be applicable to a broad range of metal oxide perovskites for artificial photosynthesis.

■ DRSET・2021 (Letter) ETRAPD　 M. Kobielusz, A. Nitta, W. Macyk* and B. Ohtani*, Combined Spectroscopic Methods of Determination of Density of Electronic States-Comparative Analysis of Diffuse Reflectance Spectroelectrochemistry and Reversed Double-Beam Photoacoustic Spectroscopy, J. Phys. Chem. Lett., 12, 3019-3025 (2021).* [DOI] ●大谷研究室で開発した逆二重励起光音響分光法（RDB-PAS）とマシック研究室で開発した電気化学拡散反射分光法をつかって共通の酸化チタン試料を分析した結果を比較し，本質的に「おなじもの＝空の電子準位」のエネルギー分布を測定していることをしめした国際共同研究．

■ CUXOT・2021 (Article) ETRAPD　 K. Wang, Z. Bielan, M. Endo-Kimura, M. Janczarek*, D. Zhang, D. Kowalski, A. Zielinska-Jurek, A. Markowska-Szczupak, B. Ohtani and E. Kowalska*, On the mechanism of photocatalytic reactions on CuxO@TiO2 core-shell photocatalyst, J. Mater. Chem. A, 9, 10135-10145 (2021).* [DOI]

■ ICTEL・2021 (letter) ETRAPD　 Y. Shen, A. Nitta, M. Takashima* and B. Ohtani, Do particles interact electronically? ―Proof of Interparticle Charge-Transfer Excitation between Adjoined Anatase and Rutile Particles, Chem. Lett., 50, 80-83 (2021).* [DOI] ●二重励起光音響分光法による電子トラップ密度のエネルギー分布解析をアナタース−ルチル混合粉末に適用した結果，ルチルの価電子帯からアナタースの電子トラップへの「界面電子移動励起」がおこること，および，価電子帯中の高密度電子レベルについて，ルチルがアナタースより約0.2 eV高いことをあきらかにした． Here, we report experimental evidence of interparticle spatial overlapping of orbitals to result in interparticle charge-transfer excitation (ICTE) at an anatase-rutile interface which is expected to be applicable to clarify the relative band position of metal-oxides and mixture homogeneity of mixture samples measured by reversed double-beam photoacoustic spectroscopy.

■ SEPIO・2020 (Full Paper) ETRAPD　 C. Chuaicham, R. R. Pawar, S. Karthikeyen, B. Ohtani and K. Sasaki*, Fabrication and characterization of ternary sepiolite/g-C3N4/Pd composites for improvement of photocatalytic degradation of ciprofloxacin under visible light irradiation, J. Colloid Interface Sci., 577, 397-405 (2020).* [DOI] ●粘土鉱物に担持させたグラファイト状窒化炭素光触媒のキャラクタリゼーションに電子トラップ密度エネルギー分布解析を利用した国際共同研究 The development of high-quality photocatalytic materials for the degradation of organic pollutants under visible light irradiation is a vital field of research. In the present study, a composite of natural sepiolite clay and synthetic graphitic carbon nitride (CN) mixed with dispersed palladium nanoparticles was developed for the efficient photocatalytic degradation of ciprofloxacin (CIP) under visible light irradiation. The sepiolite, CN, and composite materials were characterized by several techniques. The sepiolite/CN composite (SC30%) displayed superior activity than pristine sepiolite and CN, resulted from the generation of new electron trap states in the interfacial contract between sepiolite and CN to suppress the charge recombination of CN. Furthermore, the well-dispersed of 1 wt% Pd-nanoparticles in the SC30% composite collectively enhanced CIP degradation by avoiding the recombination of photogenerated electrons and holes. Additionally, the electron trap states on the surface of all samples were studied using novel reversed double-beam photoacoustic spectroscopy to understand electron transfer in the composites related to the photocatalytic degradation mechanism of CIP. The developed sepiolite/CN/Pd(0) composite can act as a potential catalyst for the degradation of organic pollutants in wastewater under visible light irradiation.

■ SANOA・2020 (Full Paper) ETRAPD　 K. Sano, F. Kuttassery, T. Shimada, T. Ishida, S. Takagi, B. Ohtani, A. Yamakata, T. Honma, H. Tachibana and H. Inoue*, Optically Transparent Colloidal Dispersion of Titania Nanoparticles Storable for longer than One year Prepared by Sol/Gel Progressive Hydrolysis/Condensation, ACS Appl. Mater. Interfaces, 12, 44743-44753 (2020).* [DOI] The molecular catalyst sensitized system (MCSS), where an excited molecular catalyst adsorbed on a semiconductor such as TiO2 injects electrons to the conduction band of the semiconductor leading to hydrogen evolution/CO2 reduction coupled with an oxidation of water on the molecular catalyst, has been one of the most probable candidates in the approach to artificial photosynthesis. For a full utilization of visible light, however, a serious light scattering of the aqueous suspension of TiO2 in the visible region, which is generally experienced, should be avoided. Here, we report a preparation of optically transparent colloidal dispersion of TiO2 by the sol/gel reaction of TiCl4 through progressive hydrolysis/condensation under the basic condition without any calcination processes. The TiO2 nanoparticles (TiO2(NPs)) obtained were characterized as an amorphous particle (~10-15 nm) having a microcrystal domain of anatase within several nm by XRD, Raman spectroscopies, XRF, XAFS, TG/DTA, and HRTEM, respectively. The energy-resolved distribution of carrier electron traps in TiO2(NPs) as a fingerprint of TiO2 was characterized through reversed double-beam photo-acoustic spectroscopy to have a close similarity to that of TiO2(ST-01) as well as the observation of carrier traps by transient absorption spectroscopy. Though the powder TiO2(NP) itself was not dispersed well in aqueous solution, the wet TiO2(NPs) as prepared before being dried up provided a completely transparent aqueous dispersion under the acidic condition (1 M HCl). Addition of methanol enabled the colloidal dispersion (TiO2(NPs, MeOH/H2O, 0.1 M HCl)) to keep the optical transparency for longer than 1 year (550 days), which is the first example of TiO2 dispersion storable for such a long period. TiO2(NPs, MeOH/H2O) exhibited a moderate photocatalytic reactivity of H2 evolution with a quantum yield of ~2.6% upon 365 nm light irradiation. An optically transparent thin film of TiO2(NPs, MeOH/H2O) was also successfully prepared on a glass plate to exhibit an enhanced hydrophilicity upon UV light irradiation.

■ GUYSB・2020 (Full length article) ETRAPD　 K. Vibulyaseak, B. Ohtani and M. Ogawa*, Crystallization of well-defined anatase nanoparticles in SBA-15 for the photocatalytic decomposition of acetic acid, RSC. Adv., 10, 32350-32356 (2020).* [DOI] Anatase nanoparticles with a size of ca. 5 nm were prepared in mesoporous silica (SBA-15 with the pore diameter of 6 nm) by impregnation of the precursor derived from titanium tetraisopropoxide and subsequent heat treatment in air. The mesoporous structure of the anatase-silica hybrid and the size of the anatase particles were kept unchanged during the crystallization of anatase at 200-600 °C. The hybrids were applied as a photocatalyst for the decomposition of acetic acid in water under UV irradiation to find the heat treatment over 400 °C led to higher efficiency of the reaction (45-55 μmol h−1 of carbon-dioxide production) over the samples heated at temperatures lower than 300 °C (3-14 μmol h−1 of carbon-dioxide production).

■ XINTO・2020 (Communication) ETRAPD　 F. Yu, C. Wang*, Y. Li, H. Ma, R. Wang, Y. Liu, N. Suzuki, C. Terashima, B. Ohtani, T. Ochiai, A. Fujishima and X. Zhang*, Enhanced Solar Photothermal Catalysis over Solution Plasma Activated TiO2, Adv. Sci., 7, 2000204 (2020).* [DOI] ●溶液中プラズマ処理により活性化した酸化チタン粒子のキャラクタリゼーションに電子トラップ密度エネルギー分布解析を利用した国際共同研究 Colored wide‐bandgap semiconductor oxides with abundant mid‐gap states have long been regarded as promising visible light responsive photocatalysts. However, their catalytic activities are hampered by charge recombination at deep level defects, which constitutes the critical challenge to practical applications of these oxide photocatalysts. To address the challenge, a strategy is proposed here that includes creating shallow‐level defects above the deep‐level defects and thermal activating the migration of trapped electrons out of the deep‐level defects via these shallow defects. A simple and scalable solution plasma processing (SPP) technique is developed to process the presynthesized yellow TiO2 with numerous oxygen vacancies (Ov), which incorporates hydrogen dopants into the TiO2 lattice and creates shallow‐level defects above deep level of Ov, meanwhile retaining the original visible absorption of the colored TiO2. At elevated temperature, the SPP‐treated TiO2 exhibits a 300 times higher conversion rate for CO2 reduction under solar light irradiation and a 7.5 times higher removal rate of acetaldehyde under UV light irradiation, suggesting the effectiveness of the proposed strategy to enhance the photoactivity of colored wide‐bandgap oxides for energy and environmental applications.

■ ZCATE・2020 (解説) ETRAPR　 大谷文章・高島舞，半導体光触媒の電子トラップ密度分布解析，触媒，62，271-276（2020）* [LINK] ほとんどの金属酸化物は，空の電子準位である「電子トラップ」をもつ．逆二重励起光音響分光法により測定できるこの電子トラップ密度のエネルギー分布（ERDT）が，粉末などの固体表面の構造を敏感に反映することがわかってきた．本稿では，このERDT解析の手法と，光触媒をはじめとする固体材料への適用についてのべる．Almost all the semiconducting metal oxides have electron traps，vacant electronic states. Newly developed reversed double-beam spectroscopy enables the measurement of energy-resolved distribution of electron traps "ERDT"，which reflects the surface structure of solid samples. In this article，principle of ERDT analysis and its application for solid materials such as photocatalysts are interpreted.

■ HANGG・2020 (Full Paper) ETRAPD　 H. Sudrajat*, M. Kitta, R. Ito, S. Nagai, T. Yoshida, R. Katoh, B. Ohtani, N. Ichikuni and H. Onishi, Water-Splitting Activity of La-Doped NaTaO3 Photocatalysts Sensitive to Spatial Distribution of Dopants, J. Phys. Chem. C, 124, 15285-15294 (2020).* [DOI] ●ランタンをドープしたタンタル酸ナトリウム光触媒のキャラクタリゼーションに電子トラップ密度エネルギー分布解析を利用した国際共同研究 Understanding the science behind highly active materials is essential for advancement in the field of photocatalytic water splitting for solar energy harvesting. Sodium tantalate (NaTaO3) doped with La cations is one of the best engineered materials for efficient water splitting to evolve hydrogen. In this study, physical insights into the sensitivity of the water-splitting activity to the spatial La distribution are discussed. The spatial distribution of La cations placed at the Na site was found to dictate the energy gradient of the conduction band bottom (CBB), resulting in a tunable electron population and hence water-splitting activity. A less homogeneous sample with a sufficiently large CBB gradient exhibited higher water-splitting activity. The mechanism of gradient tuning of the CBB through controlling the spatial dopant distribution is expected to be applicable to a broad range of metal oxide perovskites for artificial photosynthesis.

■ NGKWA・2020 (article) ETRAPD　 H. Nagakawa, T. Ochiai, H. Ma, C. Wang, X. Zhang, Y. Shen, M. Takashima, B. Ohtani and M. Nagata*, Elucidation of the electron energy structure of TiO2(B) and anatase photocatalysts by analysis of electron trap density, RSC Adv., 10, 18496 -18501 (2020).* [DOI] ●アナタースとTiO2(B)酸化チタン混合物にRDB-PAS解析を適用し，両者のあいだに界面電子移動励起がおこることおよび価電子帯中のDOSにちがいがあることを明らかにした国際共同研究 A clear understanding of the electron energy structure of TiO2(B)/anatase is needed to study the related catalytic reactions and design new composite photocatalysts. In this study, the electron energy structures of TiO2(B) and anatase were estimated by analyzing the energy-resolved distribution of electron traps measured by reversed double-beam photoacoustic spectroscopy. In the mixture of TiO2(B) and anatase, interfacial charge-transfer excitation from anatase to electron traps of TiO2(B) was suggested. By analyzing this for TiO2(B), the electron level with a relatively high density of states was found to be located ~0.07 eV deeper than that for anatase. Furthermore, a similar electron energy structure was suggested for a composite photocatalyst having a mixed phase of TiO2(B) and anatase.

■ SNGCN・2020 (Communication) ETRAPD　 C. Chuaicham, S. Karthikeyan, R. R. Pawar, Y. Xiong, I. Dabo, B. Ohtani, Y. Kim, J. T. Song, T. Ishihara and K. Sasaki*, Energy-resolved distribution of electron traps for O/S-doped carbon nitrides by reversed double-beam photoacoustic spectroscopy and the photocatalytic reduction of Cr(VI), Chem. Commun., 56, 3793-3796 (2020).* [DOI] ●非金属酸化物半導体としてはじめて窒化炭素にRDB-PAS解析を応用して，ほかの測定法ではえられない表面構造のちがいを電子トラップ密度のエネルギー分布によりあきらかにした国際共同研究 We report for the first time to our knowledge the identification of heteroatom-doped and undoped C3N4 with the energy-resolved distribution of electron traps (ERDT) near the conduction band bottom position (CBB) using reversed double-beam photoacoustic spectroscopy. The ERDT/CBB pattern is used to classify the type of elemental doping in C3N4, related to photocatalytic efficiency.

■ SNGZT・2020 (full paper) ETRAPD　 C. Chuaicham, S. Karthikeyan, J. T. Song, T. Ishihara, B. Ohtani and K. Sasaki*, Importance of ZnTiO3 phase in ZnTi-mixed metal oxide photocatalysts derived from layered double hydroxide, ACS Appl. Mater. Interfaces, 12, 9169-9180 (2020).* [DOI] ●複合金属酸化物光触媒のキャラクタリゼーションに電子トラップ密度エネルギー分布解析を利用した国際共同研究 In this study, ZnTi-mixed metal oxides (ZTM), such as ZnTiO3, were synthesized from ZnTi layered double hydroxides by varying the molar ratio of Zn/Ti, calcination temperatures, and synthesis methods (hydrothermal or reflux). The surface electronic characteristics of ZTM were investigated by the energy-resolved distribution of electron traps (ERDTs) using reversed double-beam photoacoustic spectroscopy. The ZTM samples obtained by conducting hydrothermal synthesis at 500 °C showed similar ERDT patterns independent of the molar ratio of Zn/Ti, although ZnTiO3 phase was not observed in the X-ray diffraction pattern, when the Zn/Ti ratio was high. When the ERDT patterns demonstrated a high electron accumulation level near the conduction band bottom in hydrothermal products at 500 °C, a higher photocatalytic phenol degradation efficiency was observed due to the formation of ZnTiO3 phase. This suggested that the product with the high Zn/Ti molar ratio (Zn/Ti = 6) constituted amorphous ZnTiO3.The enhanced photocatalytic performance of ZTM could be attributed to the heterojunction of electrons among ZnO, TiO2, and ZnTiO3, which enabled electron transfer in the composites, prevented charge recombination, and promoted a wider visible light adsorption by ZnTiO3 phase irrespective of its crystallinity.

■ PREEY・2019 (Article) ETRAPD　 P. Unwiset, G. Chen, B. Ohtani and K. Chayakul Chanapattharapol*, Correlation of the Photocatalytic Activities of Cu, Ce and/or Pt-Modified Titania Particles with their Bulk and Surface Structures Studied by Reversed Double-Beam Photoacoustic Spectroscopy, Catalysts, 9, 1010 (2019).* [DOI] ●銅，セリウムあるいは白金で表面を修飾した酸化チタンの逆二重励起光音響分光法による電子トラップ密度のエネルギー分布解析をふくむ各種の手法でのキャラクタリゼーションと光触媒活性に関するタイコンケーン大学との国際共同研究． Modified titania photocatalyst powder samples were prepared using the sol-gel method for copper (Cu) and cerium (Ce) doping and impregnation for platinum (Pt) loading. Their bulk crystalline structures were investigated using X-ray diffractometry (XRD) with the Rietveld analysis. The surface/bulk structure, surface properties, and morphologies were observed using reversed double-beam photoacoustic spectroscopy (RDB-PAS), nitrogen adsorption, and scanning electron microscopy, respectively. The results from the XRD revealed that all samples were mainly anatase (ca. 80% or higher) with small amounts of rutile and non-crystalline components. The specific surface areas of all samples were in the range of 115-155 m2 g−1. Ce and Cu species were mainly distributed, while Pt was potentially loaded as a partially oxidized form on the titania surface. The results from the RDB-PAS indicated the changing of the energy-resolved distribution of electron traps (ERDT) from the original titania surface upon doping of the metals (Cu, Ce, and Pt), which altered their catalytic activities. The metals photocatalytic activities with UV irradiation were measured in two representative reactions; (a) CO2 evolution from acetic acid under the aerobic condition and (b) H2 evolution from deaerated aqueous methanol. In reaction (a), the Cu and/or Ce modification gave almost the same or slightly lower activity compared to the non-modified titania samples, while platinum loading yielded ca. 5-6 times higher activity. For reaction (b), the photocatalytic tests were divided into two sets; without (b1) and with (b2) Pt deposition during the reaction. Similar enhancements of activity from the Pt loading sample (and by Cu modification) were observed in reaction (b1) without in-situ platinum deposition, while the unmodified and Ce-doped samples were almost inactive. For the activities of reaction (b2) with in-situ platinum deposition, the unmodified samples showed the highest activity while the Cu-modified samples showed significantly lower activity.

■ RATOV・2019 (full paper) ETRAPD　 M. Ratova*, L. Tosheva, P. J. Kelly and B. Ohtani, Characterisation and properties of visible light-active bismuth oxide-titania composite photocatalysts, Sust. Mater. Tech., 22, e00112 (2019).* [DOI] ●電子トラップ密度のエネルギー分布解析をビスマス酸化物光触媒に対して適用した国際共同研究 Bismuth oxide - titanium dioxide composite materials were produced by pulsed DC reactive magnetron sputtering onto two types of commercially available titanium dioxide nanoparticles. The use of an oscillating bowl enabled deposition of bismuth oxide uniformly onto loose powders, in contrast to solid substrates typically used for the conventional magnetron sputtering processes. Variation of the deposition time allowed the production of composite materials with different amounts of bismuth oxide. The composite materials, as well as uncoated titania powders, were extensively analysed by a range of analytical techniques, including SEM/EDX, XRD, BET, XPS, TEM and UV-visible diffuse reflectance spectroscopy. Photocatalytic properties of the materials were assessed under simulated visible light irradiation via degradation of acetone and methanol through measurements of carbon dioxide evolution. Additionally, the composite materials were characterised with a newly developed technique of reversed double-beam photoacoustic spectroscopy in order to obtain information on the distribution of electron traps. Bismuth oxide was found in crystalline β-Bi2O3 form on both types of substrates without any additional heat treatment applied. Though the distribution of bismuth oxide on titanium dioxide was found to depend strongly on particle size and deposition time used, the composite materials exhibited significantly enhanced visible light photocatalytic activity compared to either of the commercial titania materials used as a substrate.

■ MAITA・2019 (full paper) ETRAPD　 M. M. Maitani, A. Tateyama, P. P. Boix, G. Han, A. Nitta, B. Ohtani, N. Mathews and Y. Wada*, Effects of energetics with {001} facet-dominant anatase TiO2 scaffold on electron transport in CH3NH3PbI3 perovskite solar cells, Electrochim. Acta, 300, 445-454 (2019).* [DOI] ●電子トラップ密度のエネルギー分布解析をペロブスカイト太陽電池の酸化チタン層に適用した国際共同研究 The anatase titania with large fraction of {001} facet on the mesoscopic anatase titania scaffold in the hybrid perovskite solar cells exhibited higher photocurrent and open-circuit voltage. The higher performance with {001}-dominant anatase titania with the fraction of 74% were discussed with the characteristic electron transport properties in addition to the energy levels of trap states and conduction band as compared with those properties of conventional anatase titania scaffold. The resulted higher photocurrent and open-circuit voltage were attributed to the enhancement of the electron injection and suppression of the carrier recombination, respectively, at the titania/perovskite semiconductor interface.

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● （category = ETRAP） (59 hits)

■ TRYBA・2019 (full paper) ETRAPD　 B. Tryba*, S. Jafari, M. Sillanpaa, A. Nitta, B. Ohtani and A. W. Morawski, Influence of TiO2 structure on its photocatalytic activity towards acetaldehyde decomposition, Appl. Surf. Sci., 470, 376-385 (2019).* [DOI] ●電子トラップ密度のエネルギー分布解析をドープ型酸化チタンに適用したポーランド西ポメラニア工科大学のモラウスキ（Antoni. W. Morawski）教授のグループとの国際共同研究 Sol-gel method was used for preparation of TiO2 having different structure and phase composition. Prepared titania samples were applied for acetaldehyde decomposition under UV light irradiation. The obtained results showed, that TiO2 consisted from mixed phases of anatase and brookite, which was prepared at neutral pH and calcined at 450 °C was the most active. Charge separation of free carriers was investigated by measurements of electron traps density. It was proved, that density of electron traps can be enhanced by nitrogen doping or by coexisting of two phases such as anatase and brookite. However nitrogen doping to TiO2 did not increase of its photocatalytic activity towards acetaldehyde decomposition. Therefore preparation of TiO2 having mixed phases of anatase and brookite appeared to be the most favourable towards elimination of acetaldehyde under UV at ambient conditions. Moreover, temperature of calcination such as 450 °C was the most optimal, because at that temperature total crystallisation of amorphous titnia occurrs and then interparticle contact increases, which facilitates the interfacial charge transfer between titania particles.

■ ETIDN・2019 (full paper) ETRAPD　 A. Nitta, M. Takashima*, M. Takase and B. Ohtani, Identification and characterization of titania photocatalyst powders using their energy-resolved distribution of electron traps as a fingerprint, Catal. Today, 321-322, 2-8 (2019).* [DOI] [LINK] ●逆二重励起光音響分光法によりえられるERDT/CBB（電子トラップ密度のエネルギー分布/伝導帯下端エネルギー）パターンを「指紋」ともちいることにより，酸化チタンをはじめとする金属酸化物粉末（固体）試料の同定が可能であることを実証した． Here we report identification of powders of titania, one of the most important metal oxides, with their energy-resolved distribution of electron traps (ERDT), as a fingerprint, measured by reversed double-beam photoacoustic spectroscopy (RDB-PAS). The ERDT patterns combined with conduction-band bottom (CBB) position data measured by ordinary PAS for various titania powders and other metal-oxide powders were different depending on the kind of sample. The degree of coincidence (ζ) of ERDT/CBB patterns was evaluated for a given pair of samples as a product of each degree of coincidence for ERDT-pattern matching, total density of electron traps and CBB position. Titania samples collected from close positions in a container exhibited high values of ζ, while samples with different code names showed low values of ζ, except for pairs of samples prepared in the same way but coded differently. It was shown that the higher was the values of ζ, the higher was the degree of coincidence for photocatalytic activity of titania samples. ERDT/CBB-pattern arrays arranged in the order of photocatalytic activities in three reaction systems suggested preferable patterns for each photocatalytic reaction.

■ PKVWO・2018 (Article) ETRAPD　 P. Ketwong*, M. Takashima, A. Nitta, P. Pookmanee and B. Ohtani, Hydrothermal synthesis and photocatalytic activities of stabilized bismuth vanadate/bismuth tungstate composites, J. Environ. Chem. Eng., 6, 2048-2054 (2018).* [DOI] [HUSCAP] ●電子トラップ密度のエネルギー分布解析をビスマス系複合酸化物光触媒に適用した国際共同研究 Bismuth vanadate/bismuth tungstate (BVO/BWO) composites in various BVO fractions (f(V)) were synthesized through hydrothermal reaction. Morphology analysis of the composites showed that rod-like BVO structures were partially deposited on flake-ball (FB) BWO particles. In addition, surface structures of BWO, BVO and BVO/BWO were studied in energy-resolved distribution of electron traps and conduction band-bottom (CBB) position by household reversed double-beam photoacoustic spectroscopy (PAS) and single-beam PAS, respectively. Apparent CBB of BVO/BWO was ca. 0.4 eV anodically shifted from BWO and almost similar to BVO. Moreover, photocatalytic oxygen liberation under irradiation of UV-vis and visible lights demonstrated that photocatalytic activities of the BVO/BWO composites were depended on f(V) and calcined BVO/BWO composites in which BVO was stabilized on BWO showed enhancement of photocatalytic activity comparing to a pristine BVO. The prolonged and the highest active photocatalyst under visible light was calcined 0.80 f(V)due to BVO stabilization on FB-BWO particles.

■ RDBPF・2018 (full paper) ETRAPD　 A. Nitta, M. Takashima*, N. Murakami, M. Takase and B. Ohtani, Reversed double-beam photoacoustic spectroscopy of metal-oxide powders for estimation of their energy-resolved distribution of electron traps and electronic-band structure, Electrochim. Acta, 264, 83-90 (2018).* [DOI] [LINK] [HUSCAP] ●逆二重励起光音響分光法についてその原理と測定の実際について詳細に検討したフルペーパーで，本手法では，一定の測定条件をクリアすれば測定装置の仕様によらず原理に忠実にERDT/CBB（電子トラップ密度のエネルギー分布/伝導帯下端エネルギー）パターンがえられることをしめした． A novel instrumental methodology, reversed double-beam photoacoustic spectroscopy (RDB-PAS), was developed for measuring the energy-resolved distribution of electron traps (ERDT) of metal-oxide powders. In the RDB-PAS measurement, electrons in the valence band of a powder sample are directly excited to electron traps (ETs) and accumulated in the ETs from the deeper (anodic) side to the shallower (cathodic) side by wavelength-scanned continuous light, and the increase in photoabsorption of electron-filled ETs is measured by modulated light at a fixed wavelength by PAS. It was shown that ERDT/CBB (conduction-band bottom) patterns measured by RDB-PAS can be used for not only identification and detailed characterization of a wide range of metal-oxide powder samples but also estimation of difference in apparent valence-band top (VBT) position.

■ BEATA・2018 (full paper) ETRAPD　 B. Tryba*, M. Wozniak, G. Zolnierkiewicz, N. Guskos, A. W. Morawski, C. Colbeau-Justin, R. Wrobel, A. Nitta and B. Ohtani, Influence of an electronic structure of N-TiO2 on its photocatalytic activity towards decomposition of acetaldehyde under UV and fluorescent Lamps Irradiation, Catalysts, 8, 85 (2018).* [DOI] [HUSCAP] ●窒素ドープ酸化チタンのキャラクタリゼーションとして逆二重励起光音響分光法による電子トラップ密度のエネルギー分布解析をおこなったポーランド西ポメラニア工科大学のモラウスキ（Antoni. W. Morawski）教授のグループとの国際共同研究 The electronic structure of N-TiO2 samples prepared by a sol-gel method was investigated by EPR (Electronic Paramagnetic Resonance) measurements and the energy-resolved distribution of electron traps. In EPR spectra, some of the resonance lines assigned to paramagnetic species of nitrogen and Ti3+ were detected. Sample prepared at 300 °C revealed the highest intensity line of the nitrogen paramagnetic centers, whereas that prepared at 400 °C showed a paramagnetic line for Ti3+. Measurements of the electron trap distribution showed higher density of electron traps for sample prepared at 400 °C than that at 300 °C. Sample prepared at 300 °C, which revealed the highest amount of nitrogen built in the titania in the interstitial position was the most active under visible light. It was evidenced that photocatalytic decomposition of acetaldehyde was dependent strongly on the BET surface area and electrokinetic potential of the photocatalyst surface. The UV content in the fluorescent lamp affected the yield of acetaldehyde decomposition.

■ ZFUNT・2017 (解説) ETRAPR　 新田明央・高島舞・高瀬舞・大谷文章，電子トラップ密度のエネルギー分布解析−金属酸化物粉末粒子の評価と同定をめざして，粉体工学会誌，54，560-568（2017） [DOI] [LINK] ●逆二重励起光音響分光法による半導体材料の精密構造評価と同定について，とくに酸化チタン粉末の例を中心にして，基礎から応用までをしめした解説． Here we propose a method for identification and characterization of metal-oxide powders with patterns of energy-resolved density of electron traps（ERDT) and conduction-band bottom (CBB) position，as a fingerprint，measured by newly developed reversed double-beam photoacoustic spectroscopy (RDB-PAS） Degrees of coincidence (ζ) of ERDT/CBB patterns could be quantitatively evaluated for a given pair of titania samples as a product of coincidence of (a) ERDT-pattern matching，(b) total density of electron traps，and (c) CBB position estimated by ordinary PAS. It was also shown that the higher the ζ is increased，the higher the degree of coincidence for photocatalytic activities of the pair of titania samples becomes regardless of three different photocatalytic reaction systems，presumably because photocatalytic activities are regulated by ERDT and CBB of titania powders.

■ RDBPL・2016 (Communication) ETRAPD　 A. Nitta, M. Takase, M. Takashima, N. Murakami and B. Ohtani, A Fingerprint of Metal-oxide Powders: Energy-resolved Distribution of Electron Traps, Chem. Commun., 52, 12096-12099 (2016).* [DOI] [HUSCAP] ●逆二重励起光音響分光法（RDB-PAS）を開発し，金属酸化物中の電子トラップ密度のエネルギー分布（ERDT）を精度よくかつ比較的簡便に測定できることをしめした．また，ERDTと伝導帯下端位置（CBB）を価電子帯上端（VBT）からのエネルギーの関数としてプロットしたERDT/CBBパターンを「指紋」としてもちいることによって金属酸化物粉末試料の同定が可能であることを提案した． Here we propose a method for the identification of metal-oxide powders with the energy-resolved distribution of electron traps and conduction-band bottom position reflecting a surface structure and a bulk structure, respectively, as a fingerprint, based on the degree of coincidence for a given pair of samples, measured using newly developed reversed double-beam photoacoustic spectroscopy.

■ MKM・2007 (full paper) ETRAPD　 S.-y. Murakami, H. Kominami*, Y. Kera, S. Ikeda, H. Noguchi, K. Uosaki and B. Ohtani, Evaluation of electron-hole recombination properties of titanium(IV) oxide particles with high photocatalytic activity, Res. Chem. Interm., 33, 285-296 (2007).* [DOI] [HUSCAP] ●水のかわりに有機溶媒をつかう高温加圧合成法であるソルボサーマル法により合成した高活性酸化チタン光触媒の再結合挙動をフェムト秒ポンプ―プローブ測定により解析し，活性が高いものほど再結合が遅いことをしめした．三価チタン種密度を光化学法により定量し，光触媒の非表面積に対して直線的に増加すること，および，トラップ電子の減衰速度定数と相関があることを見いだした． Electron-hole recombination in nano-sized titanium(IV) oxide (TiO2) particles with various physical properties, which have been shown to be highly active photocatalysts, was evaluated by quantitative analysis of reduced titanium species (Ti3+), which might be formed at crystalline defective sites in TiO2 particles through photo-irradiation in the presence of a hole scavenger under deaerated conditions. These highly active photocatalyst samples were synthesized by hydrothermal crystallization in organic media (HyCOM method) and post-calcination. The Ti3+ density decreased with increasing calcination temperature (T c), and a linear correlation was observed between the Ti3+ density and rate constant for electron-hole recombination evaluated by femtosecond pump-probe diffuse reflection spectroscopy. Reaction rate (R Ag) and the amount of silver ions (Ag+) adsorbed on TiO2 particles ([Ag+]ads) were measured for photocatalytic silver metal deposition along with oxygen formation from an aqueous Ag+ solution under deaerated conditions, and the slope of the R Ag versus [Ag+]ads plot was determined. Kinetic investigation of this reaction showed that the reciprocal of the slope was approximately related to the ratio of the rates for electron-hole recombination and electron trapping (k r/k e ratio). The k r/k e ratio decreased as T c increased, and the logarithm of the k r/k e ratio was linearly related with Ti3+ density. These two parameters were used as a measure for the recombination properties of TiO2 photocatalysts with various physical properties.

■ TIT・2003 (full paper) ETRAPD　 S. Ikeda, N. Sugiyama, S.-y. Murakami, H. Kominami, Y. Kera, H. Noguchi, K. Uosaki, T. Torimoto and B. Ohtani*, Quantitative Analysis of Defective Sites in Titanium(IV) Oxide Photocatalyst Powders, Phys. Chem. Chem. Phys., 5, 778-783 (2003).* [DOI] [HUSCAP] ●酸化チタン光触媒中の電子トラップ密度を，光化学反応により蓄積させた電子をメチルビオロゲンに定量的に移動させ，生じるメチルビオロゲンカチオンラジカルを分光学的に定量する手法を確立するとともに，電子トラップのエネルギー位置がアナタースとルチルのいずれの場合でも伝導帯下端から約100 mVアノード側にあることをしめした．逆二重励起光音響分光法が開発されるまでは，電子トラップのエネルギー分布をしめした唯一の論文． The molar amounts of defective sites (Md) in several titanium(IV) oxide (TiO2) powders were determined using photoinduced reactions of electron accumulation in deaerated aqueous solutions containing sacrificial hole scavengers and subsequent reduction of methylviologen to its cation radical. Measurements of pH dependence of typical anatase and rutile TiO2 powders showed that these defective sites were of electronic energy just below the conduction band edge of TiO2 in ranges of 0-0.35 V for anatase and 0-0.25 V for rutile. A linear relation of Md with the rate constant of electron-hole recombination determined by femtosecond pump-probe diffuse reflection spectroscopy revealed that Md could be a quantitative parameter of recombination between a photoexcited electron and a positive hole. The fact that there was no linear relation between Md and the specific surface area suggests that the surface area was not directly reflected on Md. A reciprocal correlation between photocatalytic activity for water oxidation in aqueous silver sulfate solution and Md revealed that the rate of recombination is one of the predominant physical properties governing the activities of TiO2 powders in this reaction system.

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