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Your search keyword '"Eishi Tanabe"' showing total 6 results
Start Over "Eishi Tanabe" Publisher royal society of chemistry
6 results on '"Eishi Tanabe"'

1. Transient nature of graphene quantum dot formation via a hydrothermal reaction

Author

Ogi, Takashi, Iwasaki, Hideharu, Aishima, Kana, Iskandar, Ferry, Wang, Wei-Ning, Takimiya, Kazuo, Okuyama, Kikuo, Ogi, Takashi, Iwasaki, Hideharu, Aishima, Kana, Iskandar, Ferry, Wang, Wei-Ning, Takimiya, Kazuo, and Okuyama, Kikuo

Abstract

type:text, A facile, economic and environmentally friendly one-step approach for the preparation of highly luminescent graphene quantum dots (GQDs) was developed using a hydrothermal reaction between citric acid and urea. Unlike previous reports, we focused on the effect of the transient nature of GQD formation on the photoluminescence (PL) properties and molecular structure changes of the products. We found that the GQDs have an optimum reaction time and require an effective precursor to achieve excellent luminescent properties. The PL, ultraviolet-visible (UV-vis) absorption, zeta potential, and nuclear magnetic resonance (NMR) analyses of the GQDs prepared at various reaction times revealed that the molecular structures responsible for the luminescence of the GQDs are aggregates or condensation products of citric acid amides. We found that urea addition to the precursor drastically enhances the PL intensity of the GQDs, and it is 40 times higher than those prepared using the pure citric acid precursor. Additionally, a GQDs–polyvinyl alcohol composite achieved an excellent quantum yield (QY) of 43.6%., This work was supported by JSPS KAKENHI Grant numbers 26709061 and 24656413. We thank Dr Eishi Tanabe from the Hiroshima Prefectural Institute of Industrial Science and Technology for helping with TEM analyses, and Drs Naoya Tochio and Junichi Kakimura from Hiroshima University for NMR analyses.

Published
2014

2. Transient nature of graphene quantum dot formation via a hydrothermal reaction

Author

Ogi, Takashi, Iwasaki, Hideharu, Aishima, Kana, Iskandar, Ferry, Wang, Wei-Ning, Takimiya, Kazuo, Okuyama, Kikuo, Ogi, Takashi, Iwasaki, Hideharu, Aishima, Kana, Iskandar, Ferry, Wang, Wei-Ning, Takimiya, Kazuo, and Okuyama, Kikuo

Abstract

A facile, economic and environmentally friendly one-step approach for the preparation of highly luminescent graphene quantum dots (GQDs) was developed using a hydrothermal reaction between citric acid and urea. Unlike previous reports, we focused on the effect of the transient nature of GQD formation on the photoluminescence (PL) properties and molecular structure changes of the products. We found that the GQDs have an optimum reaction time and require an effective precursor to achieve excellent luminescent properties. The PL, ultraviolet-visible (UV-vis) absorption, zeta potential, and nuclear magnetic resonance (NMR) analyses of the GQDs prepared at various reaction times revealed that the molecular structures responsible for the luminescence of the GQDs are aggregates or condensation products of citric acid amides. We found that urea addition to the precursor drastically enhances the PL intensity of the GQDs, and it is 40 times higher than those prepared using the pure citric acid precursor. Additionally, a GQDs–polyvinyl alcohol composite achieved an excellent quantum yield (QY) of 43.6%., This work was supported by JSPS KAKENHI Grant numbers 26709061 and 24656413. We thank Dr Eishi Tanabe from the Hiroshima Prefectural Institute of Industrial Science and Technology for helping with TEM analyses, and Drs Naoya Tochio and Junichi Kakimura from Hiroshima University for NMR analyses.

3. Direct synthesis of carbon quantum dots in aqueous polymer solution: one-pot reaction and preparation of transparent UV-blocking films.

Author

Hess, Samuel C., Permatasari, Fitri A., Fukazawa, Hiromitsu, Schneider, Elia M., Balgis, Ratna, Ogi, Takashi, Okuyama, Kikuo, and Stark, Wendelin J.

Abstract

Carbon quantum dots (CQDs) were characterized and their synthesis optimized extensively over recent years. It is becoming more and more important to develop synthesis solutions for CQDs applications to allow simple and cheap applications with composite materials. Here, we present a one-pot CQDs reaction in an aqueous polyvinyl alcohol (PVA) solution and the synthesis of transparent UV protection films. The synthesis solution was tuned in a way that transparent UV-protection films cast from unpurified CQDs–PVA solutions could be obtained without the need of yield consuming purification steps. Measuring the impact of varying PVA, branched polyethylene imine (b-PEI), and citric acid (CA) concentrations on the solution's and film's UV/Vis transmission and absorbance allowed elucidating important factors influencing the solution to film property transition. Applying CQDs–PVA films on commercially available PET bottle films resulted in high transparency of the composite film in the visible range (＞80%) and UV absorption of over 90%. Lastly, our CQDs–PVA film performed stable UV-blocking and did not show any bleaching effects over several days of UV-exposure. [ABSTRACT FROM AUTHOR]

Published
2017
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4. Contents list.

Subjects
CHEMICAL engineering, CHEMISTS
Abstract

The table of contents for June 2016 issue of "New Journal of Chemistry" is presented.

Published
2016
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5. Direct white light emission from a rare-earth-free aluminium–boron–carbon–oxynitride phosphor.

Author

Ogi, T., Iwasaki, H., Nandiyanto, A. B. D., Iskandar, F., Wang, W.-N., and Okuyama, K.

Abstract

White light-emitting diodes offer the possibility of efficient, safe, and reliable solid-state lighting, and thus have various applications. Reported white light-emitting phosphors usually contain expensive rare-earth metals and are generally prepared by high-energy processes (e.g., >1000 °C, H2 and CO reduction atmospheres). These factors limit their applications. Therefore, preparing cost-effective white light-emitting phosphors from environmentally friendly processes is an important challenge. Herein, a direct white light-emitting aluminium–boron–carbon–oxynitride (AlBCNO) phosphor, which can be economically produced using low-energy methods (<900 °C, atmospheric conditions), is reported. To the best of our knowledge, this is the first reported rare-earth-free white light-emitting phosphor. AlBCNO emission spans the entire visible spectrum and its broad excitation spectrum is comparable to that of near-UV light-emitting diodes. Increasing the relative concentrations of B or Al in AlBCNO enables emission tuning to yellow or blue, respectively. These findings have implications for new methods of preparing white light-emitting phosphors. [ABSTRACT FROM AUTHOR]

Published
2014
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6. Transient nature of graphene quantum dot formation via a hydrothermal reaction

Author

Kikuo Okuyama, Ferry Iskandar, Kana Aishima, Wei-Ning Wang, Kazuo Takimiya, Hideharu Iwasaki, and Takashi Ogi

Subjects
Photoluminescence, Chemistry, Graphene, General Chemical Engineering, Inorganic chemistry, Quantum yield, General Chemistry, Graphene quantum dot, law.invention, chemistry.chemical_compound, Chemical engineering, Quantum dot, law, Zeta potential, Citric acid, Luminescence
Abstract

A facile, economic and environmentally friendly one-step approach for the preparation of highly luminescent graphene quantum dots (GQDs) was developed using a hydrothermal reaction between citric acid and urea. Unlike previous reports, we focused on the effect of the transient nature of GQD formation on the photoluminescence (PL) properties and molecular structure changes of the products. We found that the GQDs have an optimum reaction time and require an effective precursor to achieve excellent luminescent properties. The PL, ultraviolet-visible (UV-vis) absorption, zeta potential, and nuclear magnetic resonance (NMR) analyses of the GQDs prepared at various reaction times revealed that the molecular structures responsible for the luminescence of the GQDs are aggregates or condensation products of citric acid amides. We found that urea addition to the precursor drastically enhances the PL intensity of the GQDs, and it is 40 times higher than those prepared using the pure citric acid precursor. Additionally, a GQDs–polyvinyl alcohol composite achieved an excellent quantum yield (QY) of 43.6%., This work was supported by JSPS KAKENHI Grant numbers 26709061 and 24656413. We thank Dr Eishi Tanabe from the Hiroshima Prefectural Institute of Industrial Science and Technology for helping with TEM analyses, and Drs Naoya Tochio and Junichi Kakimura from Hiroshima University for NMR analyses.

Published
2014

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