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52. Composition control of alloy nanoparticles consisting of bulk-immiscible Au and Rh metals via an ionic liquid/metal sputtering technique for improving their electrocatalytic activity.

Author

Akiyoshi, Kazutaka, Watanabe, Yumezo, Kameyama, Tatsuya, Kawawaki, Tokuhisa, Negishi, Yuichi, Kuwabata, Susumu, and Torimoto, Tsukasa

Abstract

AuRh bimetallic alloy nanoparticles (NPs) were successfully prepared by simultaneous sputtering of Au and Rh in a room-temperature ionic liquid (RTIL) of N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate (DEME-BF4). Bimetallic AuRh alloy NPs of 1–2 nm in size were formed in the RTIL. The alloy composition was controllable by changing the surface areas of Au and Rh plates used as sputtering targets. Loading thus-obtained AuRh NPs on carbon black (CB) powders increased the size of AuRh NPs to ca. 2–8 nm, depending on the Au/Rh ratio. The electrocatalytic activity for oxygen reduction reaction (ORR) of AuRh NP-loaded CB catalysts showed a volcano-type dependence on their composition, in which AuRh NPs with Au surface coverage of 62% exhibited the optimal ORR activity, the specific activity being ca. 5 times higher than that of pure Rh NPs. [ABSTRACT FROM AUTHOR]

Published
2022
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64. Quantum-Dot Light-Emitting Diodes Exhibiting Narrow-Spectrum Green Electroluminescence by Using Ag–In–Ga–S/GaSxQuantum Dots

Author

Motomura, Genichi, Uematsu, Taro, Kuwabata, Susumu, Kameyama, Tatsuya, Torimoto, Tsukasa, and Tsuzuki, Toshimitsu

Abstract

Quantum dots (QDs), which have high color purity, are expected to be applied as emitting materials to wide-color-gamut displays. To enable their use as an alternative to Cd-based QDs, it is necessary to improve the properties of QDs composed of low-toxicity materials. Although multielement QDs such as Ag–In–Ga–S are prone to spectrally broad emission from defect sites, a core/shell structure covered with a GaSxshell is expected to enable sharp emission from band-edge transitions. Here, QD light-emitting diodes (QD-LEDs) embedded with Ag–In–Ga–S/GaSxcore/shell QDs (AIGS QDs) were fabricated, and their electroluminescence (EL) was observed. The EL spectra from the AIGS QD-LEDs were found to contain a large defect-related emission component not observed in the photoluminescence (PL) spectra of the AIGS QD films. This defect-related emission was caused by electrons injected into defect sites in the QDs. Therefore, the AIGS QDs and the electron injection layer (EIL) of ZnMgO were treated with Ga compounds such as gallium chloride (GaCl3) and gallium tris(N,N′-diethyldithiocarbamate) (Ga(DDTC)3) to improve the luminescence properties of the QD-LEDs. The added Ga compounds effectively compensated for defect sites on the surface of the QDs and suppressed direct electron injection from the EIL into defect sites. As a result, the defect-related emission components in the EL were successfully suppressed, and the EL exhibited a color purity comparable to the PL of the AIGS QD films. The QD-LEDs exhibited EL spectra with a full width at half-maximum of 33 nm, which is extremely sharp for a low-toxicity QD, and the chromaticity coordinates (0.260, 0.695) for green EL were achieved.

Published
2023
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72. Oxygen reduction at platinum monolayer islands deposited on Au(111)

Author

Kongkanand, Anusorn and Kuwabata, Susumu

Subjects
Nanoparticles -- Atomic properties, Platinum -- Atomic properties, Gold compounds -- Atomic properties, Chemicals, plastics and rubber industries
Abstract

A study is conducted for the first time on atomic monolayer islands of two-dimensional Pt nanoparticles, on an Au(111) electrode focusing on their electrocatalytic activities for oxygen reduction in acid solutions. Pt islands prepared using the self-assembled technique of thiols and the replacement of Pt with a Cu monolayer exhibited special catalytic activities for oxygen reduction.

Published
2005

74. Enhancement of light-energy conversion efficiency by multi-porphyrin arrays of porphyrin-peptide oligomers with fullerene clusters

Author

Hasobe, Taku, Fukuzumi, Shunichi, kamat, Prashant V., Kuwabata, Susumu, Troiani, Vincent, Kongkanand, Anusorn, Solladie, Nathalie, Kim, Dongho, Ahn, Tae Kyu, and Kim, Seong Keun

Subjects
Peptides -- Optical properties, Oligomers -- Optical properties, Porphyrins -- Optical properties, Chemicals, plastics and rubber industries
Abstract

The study reports novel photovoltaic cells composed of phorphyrin-peptide oligomers and fullerene clusters, which are deposited on nanostructured SnO2 electrodes. It concluded that the formation of a molecular assembly between fullerene and multi-porphyrin arrays with a polypeptide backbone controls the electron transfer efficiency in the supramolecular complex, which is essential for the light-energy conversion.

Published
2005

75. Real-time quantification of methanol in plants using a hybrid alcohol oxidase-peroxidase biosensor

Author

Hasunuma, Tomohisa, Kuwabata, Susumu, Fukusaki, Ei-ichiro, and Kobayashi, Akio

Subjects
Chemistry
Abstract

An amperometric biosensor immobilizing two enzymes and an electron mediator in an identical plane has been fabricated by the self-assembly technique for determination of methanol in crude plant samples. A self-assembled mixed monolayer of 4,4'-dithiodibutyric acid covalently attached two enzymes (Hansenula sp. alcohol oxidase and horseradish peroxidase) and 11-ferrocenyl-1-undecanethiol as an electron mediator on an Au electrode is exploited to produce a two-dimensional reaction matrix. The composition of the two enzymes and electron mediator molecules was optimized for detection of methanol in 0.1 M sodium phosphate buffer (pH 6.0). We successfully quantified methanol in low-purity tobacco (Nicotiana tabacum) plant extracts with the biosensor, which showed sensitivity comparable to that of gas chromatography/ mass spectrometry. The redox-relay biosensor is quite simple and stable due to its covalent attachment to the Au surface, making it possible to downsize the construction. We fabricated a miniature methanol biosensor that fitted a well of a 96-well micro assay plate available for high-throughput assay. The biosensor is advantageous for the sensitive, continuous, and convenient determination of methanol.

Published
2004

76. Encapsulation of AgInS2/GaSx core/shell quantum dots in In-fumarate metal–organic frameworks for stability enhancement.

Author

Tepakidareekul, Manunya, Uematsu, Taro, Torimoto, Tsukasa, and Kuwabata, Susumu

Subjects
QUANTUM dots, METAL-organic frameworks, GALLIUM, PHOTOLUMINESCENCE, SILVER sulfide
Abstract

Silver indium sulfide/gallium sulfide (AgInS2/GaSx) core/shell quantum dots (QDs), among the cadmium-free alternatives that possess a narrow band-edge emission, have attracted immense attention in recent years. However, the insufficient stability of photoluminescence (PL) due to chemically sensitive GaSx shells, which is partly caused by easy desorption of passivated ligands, remained a problem for their practical application. In this study, a simple and efficient method to protect these QDs is presented. The AgInS2/GaSx core/shell QDs are encapsulated into metal–organic frameworks (MOFs) consisting of an indium-fumarate ordered structure (InMOFs). Whereas damage to the shell during the encapsulation reaction can potentially occur, the obtained composite (AgInS2/GaSx@InMOFs) maintains a narrow band-edge emission that is mostly identical to the pristine AgInS2/GaSx core/shell QDs with a PL quantum yield (PL QY) of 12.6% after optimization of the synthesis-solution pH. The encapsulation result enables the spectral shape and PL QY of the composite to be maintained after 7 days, which demonstrates the high stability of the QDs encapsulated in InMOFs. [ABSTRACT FROM AUTHOR]

Published
2022
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