論文/publication

Environmental-friendly degradation of clay-hybridized Cu nanoparticles by carboxylic acids

Masaya Miyagawa, Yoko Ikeyama, Hitomi Kotake, Toshiki Maeda, and Hideki Tanaka
Chemical Physics Letters 753 (2020) 137615

Green degradation method of Cu nanoparticles was investigated by stepwise oxidation with air and carboxylic acid. The Cu nanoparticles were synthesized directly on kaolinite, one of the layered clay minerals. By the air exposure, the Cu nanoparticles formed Cu2O shell, which was oxidized to Cu2+ by the carboxylic acid. Degradation rate was calculated by using the absorption band of Cu2+. As a result, the Cu nanoparticles were found to be degraded almost completely regardless of valence of the carboxylic acids, while the proton in the carboxy group was significant in the oxidation of Cu2O to Cu2+.


PHOTOLUMINESCENT Cu NANOPARTICLES INDUCED BY ENERGY TRANSFER ON SAPONITE NANOSHEET

Kengo Nishio, Masaya Miyagawa, and Hideki Tanaka
Clay Sciene 23, 67-71 (2019)

Photoluminescence (PL) of metal nanoparticles (NPs) has historically been investigated with their films, where PL is enhanced by surface plasmon resonance of the NPs themselves. In contrast, it is difficult to observe the PL in colloidal dispersion probably due to too long interparticle distance. In the present study, we observed the PL by introducing Forster resonance energy transfer from acridine orange adsorbed on saponite nanosheets, where Cu NPs were synthesized directly. In the presence of the Cu NPs, the PL spectra were dramatically changed. The PL of the Cu NPs was confirmed by temperature dependency of the PL spectra.


Aqueous synthesis of protectant-free copper nanocubes by a disproportionation reaction of Cu2O on synthetic saponite

Masaya Miyaga, Miharu Usui, Yu Imura, Shota Kuwahara, Toshiki Sugai and Hideki Tanaka
Chem. Commun., 54 (2018) 5854

Here, we report a synthesis of Cu nanocubes by photoreduction of CuSO4. Because synthetic saponite (one of the layered clay minerals) was used as the adsorbent, the nanocubes contained no capping agents or protectants, and the disproportionation reaction of Cu2O with H2SO4 was found to be the key for morphological control.


Diameter-controlled Cu nanoparticles on saponite and preparation of film by using spontaneous phase separation

Masaya Miyaga, Akane Shibusawa, Kaho Maeda, Akiyoshi Tashiro, Toshiki Sugai and Hideki Tanaka
RSC Adv., 7 (2017) 41896

Cu nanoparticles have attracted much attention due to their optical, catalytic, and electrical properties. Their syntheses, however, have required hazardous reducing agents. In addition, they are easily oxidized, which destroys their properties. It has also not been possible to control the diameter and the dispersibility for further applications in functional materials. To solve these problems, we have recently synthesized oxide-free Cu nanoparticles adsorbed on kaolinite, a non-dispersive layered clay, by environmentally friendly photoreduction. Focusing on the layer charge of the clay, we report diameterand dispersibility-controlled Cu nanoparticles on saponite, a dispersive clay, in the present study. The obtained oxide-free Cu nanoparticles were stable under N2 atmosphere, while they exhibited a fast back reaction to Cu2+ upon exposure to fresh air. The diameter of the Cu nanoparticles could be controlled simply with [Cu2+], because Cu2+ was adsorbed on saponite before the photoreduction. The dispersibility of the Cu nanoparticles was controlled without changing the diameter using the size of saponite aggregates: these were stably dispersed at low [Cu2+], and flocculated at high [Cu2+]. The flocculates could be collected by filtration and the obtained viscous paste was useful for preparing a film with the optical properties of the Cu nanoparticles without aggregation. Therefore, the present study revealed that combining the adsorption of Cu2+ on saponite with photoreduction is a novel and environmentally friendly synthetic method for controlling the diameter and the dispersibility of Cu nanoparticles, and it has the potential to further their applications in functional materials


Synthesis of Truffle-shaped Oxide-free Cu Nanoparticles under Atmospheric Conditions with the Aid of Photocatalytic TiO2

Masaya Miyagawa, Takuya Aoki, Ryoya Seki, Akane Shibusawa, Hideki Tanaka
Chem. Lett. 46 (2017) 1403

Truffle-shaped Cu nanoparticles (NPs) were synthesized by photoreduction of copper acetate solution in the presence of TiO2. X-ray diffraction measurement revealed that the obtained NPs were composed of pure Cu without oxides, which was notable because the photoirradiation was performed under atmospheric conditions, where the Cu NPs are easily oxidized. The Cu NPs were dispersed stably without protectants because the TiO2 NPs adsorbed on the Cu NPs were dispersed, probably due to their electric repulsion.


Lustrous copper nanoparticle film: Photodeposition with high quantum yield and electric conductivity

Masaya Miyagawa, Mari Yonemura, Hideki Tanaka
Chem. Phys. Lett. 655 (2016) 95

Cu nanoparticle (NP) film has attracted much attention due to its high electric conductivity. In the present study, we prepared a Cu NP film on a TiO2-coated substrate by photoreduction of copper acetate solution. The obtained film showed high electric conductivity and metallic luster by the successive deposition of Cu NP. Moreover, the film was decomposed on exposure to fresh air, and its decomposition reaction mechanisms were proposed. Hence, we concluded that the obtained lustrous film was composed of Cu NP, even though its physical properties was similar to bulk copper.


Precious metal-like oxide-free copper nanoparticles: high oxidation resistance and geometric structure

Masaya Miyagawa, Toshiki Maeda, Ryo Tokuda, Akane Shibusawa, Takuya Aoki, Kazu Okumura and Hideki Tanaka
RSC Adv. 6 (2016) 104560

Cu nanoparticles have attracted much attention as an alternative to precious metal Au- and Pt-based materials. However, they have a problem with stability and get oxidized easily. Moreover, their synthesis is carried out with hazardous chemicals and in conditions, which is not environmentally friendly. Thus, both improvement in oxidation resistance and establishment of a novel synthesis method under mild conditions are desired for further applications. To solve these problems, we synthesized Cu nanoparticles from copper(II) acetate by photoreduction at room temperature in the presence of kaolinite, a layered clay mineral with high gas barrier properties. We obtained disk-like metallic Cu nanoparticles adsorbed on kaolinite without oxides. The nanoparticles showed high oxidation resistance in the solid phase. The powder sample was stable and did not get oxidized at all even after 6 months on exposure to fresh air in spite of no apparent protectants, which was revealed by infrared spectroscopy. Namely, the obtained Cu nanoparticles showed a precious metal-like property. On the other hand, the as-prepared Cu nanoparticles still showed the reactivity with fresh air in the suspension. This indicates that the adsorption on kaolinite did not spoil the reactivity of the Cu nanoparticles. Therefore, the present study revealed that the combination of photoreduction and addition of a layered clay mineral would be a promising environmentally friendly way to synthesize oxidation?resistant metal nanoparticles.


Oxidation-resistive copper nanoparticles: photoreduction synthesis and their oxidation state measurements by XAFS and HRTEM

H Tanaka, T Aoki, M Yonemura, M Miyagawa and K Okumura
J. Phys. Conf. Ser. 712 (2016) 012120

We examined the synthesis of copper nanoparticles by photoreduction, and characterized them using optical spectroscopy, XAFS measurement, and electron microscopy. Ethanol solution of copper acetate with TiO2 nanoparticles was photoirradated. Optical absorption observation indicated that copper nanoparticles were formed in the solution. XAFS measurement indicated that the nanoparticles were metallic, not oxidized. Electron microscopy observation exhibited that the nanoparticles kept metallic even under exposure to air.


Intense Plasmon-induced Cotton Effects in Colloidal Silver Triangular Nanoplates Synthesized by a Ligand-exchange Process

Naoki Nishida, Yasuhiro Kojima,Hideki Tanaka
Chem. Lett. 43(2014)1227

Chiroptically active Ag triangular nanoplates were synthesized by the ligand-exchange reaction of achiral Ag nanoplates with chiral D- or L-penicillamine molecules. Analysis of the chiroptical properties of the synthesized nanoplates by circular dichroism spectroscopy revealed intense Cotton effects, with wavelengths that corresponded to those of the surface plasmon resonances for the nanoplates. Enantiomeric excess and pH dependence of these effects were also measured to explore the origin of the chiroptical activity of the nanoplates.

Production of Oxidation-resistant Copper Nanoparticles on Carbon Nanotubes by Photoreduction

Naoki Nishida, Akira Miyashita,Tatsuya Tsukuda, Hideki Tanaka
Chem. Lett. 42(2013)168

Copper nanoparticles (Cu NPs) were produced through photoreduction of a mixture of copper acetate solution and carbon nanotubes (CNTs) at room temperature. The diameter of the NPs could be controlled by the photoirradiation time. HRTEM and XRD measurements revealed that the NPs were composed of a metallic Cu core and a Cu2O shell that acts as a passive layer.

Chiral glutathione-protected Ag triangular nanoplates synthesized by protectant-substitution reaction-chiroptical and surface structure analysis

Naoki Nishida, Yasuhiro Kojima,Hideki Tanaka
Chem. Lett. 41(2012)926

Chiral Ag:SG (glutathione) triangular nanoplates were synthesized by substitution reaction of achiral Ag:poly(vinylpyrrolidone) (PVP) nanoplates with glutathione free GSH molecules. Analysis of the chiroptical properties of the synthesized nanoplates using a circular dichroism spectrometer revealed characteristic Cotton effects with wavelengths that corresponded well to those of plasmon resonances for Ag nanoplates. X-ray photoelectron spectrometry analysis of their chemical compositions revealed that complete substitution of PVP molecules with GSH molecules proceeds on the nanoplates.

Regenerative synthesis of copper nanoparticles by photoirradiation

Naoki Nishida, Akira Miyashita, Naomi Hashimoto, Haruno Murayama, Hideki, Tanaka
Eur. Phys. J. D 63(2011)307

Copper nanoparticles have attracted much attention because of their low cost, and because their use can contribute toward the sustainability of metal resources. In this study, copper nanoparticles were synthesized by the photoirradiation of copper acetate solution at room temperature. The diameter and chemical composition of the obtained copper nanoparticles were analyzed using Field-emission scanning electron microscope (FE-SEM) spectrophotometer and an X-ray photoelectron spectrometer. Well-dispersed copper nanoparticles with 〜5 nm in diameter were observed in the solution. On the other hand, when the nanoparticle solution was exposed to fresh air, nanoparticles were not observed in the solution. Furthermore, the copper nanoparticles were recovered from a solution of decomposed nanoparticles by re-photoirradiation.

Stable Transport of Gas-born Ag Nanoparticles into Liquid Phase Mediated by Poly (vinylpyrrolidone) Molecules

Naomi Hashimoto, Naoki Nishida, Haruno Murayama, Hideki Tanaka
Chem. Lett. 40(2011)144

We demonstrate that gas-born nanoparticles can be transported into solution successfully. Our results show that Ag nanoparticles produced in gas phase are introduced into poly(vinylpyrrolidone) solution without structural changes such as nanoparticle aggregation. It is also shown that Ag nanoparticles in solution show surface plasmon resonance, suggesting that the optical properties of nanoparticles are not impaired by the transport from gas to liquid.

Number-adjustablenanoparticleclusters realized by a combination of Ag and C60 nanoparticles in the gas phase

Hideki Tanaka, Futoshi Maeda
Chemical Physics Letters 484(2009)37

We demonstrate production of nanoparticleclusters, namely clusters composed of nanoparticles, using a combination of surface-active Ag nanoparticles and surface-inactive C60 nanoparticles. The producedclusters, after diameter-selection by a differential mobility analyzer, were analyzed by field-emission scanning electronic microscopy and X-ray photoelectron spectroscopy. The produced clusters are found to be composed of outer surface-deposited Ag nanoparticles with 〜3 nm diameters that are distinctly isolated from one another and with an inner core composed of C60 molecules. The number of constituent Ag nanoparticles is adjustable by selection of the diameters of the clusters.

Ag triangular nanoplates synthesized by photo-induced reduction: Structureanalysis and stability

Haruno Murayama, Naomi Hashimoto, Hideki Tanaka
Chemical Physics Letters 482(2009)291

Ag triangular nanoplates were synthesized by photoirradiation to AgNO3 ethanol solution in the presence of polyvinylpyrrolidone (PVP) under anaerobic conditions at room temperature. High-resolution SEM and TEM observations revealed that thin Ag equilateral triangularnanoplates, each of which was a single crystal with sharp corners and flat faces presented by {1 1 1} planes, were produced. Analyses of XAFS and XPS have shown that these nanoplates are protected by coordination of O atoms in PVP molecules, not being oxidized as Ag2O. The nanoplates are inherently stable, though they were easily truncated and dissolved if mixed with oxygen or water.

Growth process of Ag triangular nanoplates observed by in situ XAFS

Haruno Murayama, Naomi Hashimoto, Hideki Tanaka
J. Phys. Conf. Ser. 190(2009)012132

We examined to establish the simple synthesis method of Ag triangular nanoplates in order to elucidate their growth process. Ethanol solution of AgNO3 was photoirradiated without reduction agents except in the presence of PVP, poly(vinil-pyrrolidone). Electron microscope observations revealed that the shape of the product was Ag triangular nanoplates with sharp corners and a flat face. In situ XAFS and optical absorption measurements suggested that the Ag triangular nanoplates were photoinduced-converted from Ag spherical nanoparticles via Ag truncated triangular nanoplates.

Production of nanoparticlescomposed of ionicliquid [C4mpyrr][NTf2] and their chemical identification by diameter analysis and X-ray photoelectron spectroscopy

Masaharu Shigeyasu, Haruno Murayama, Hideki Tanaka
Chemical Physics Letters 463(2008)373

Production of nanoparticlescomposed of ionicliquid [C4mpyrr][NTf2], N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, was demonstrated by a gas aggregation technique under low pressure. The diameter spectra were measured by a differential mobility analyzer (DMA) and were dependent on the heating temperature. Photoelectron spectra for the nanoparticles diameter-selected at 10 nm were also measured by X-ray photoelectron spectroscopy (XPS), and their chemical composition and structure were identified by comparison with photoelectron spectra for neat ionicliquid. The form and surface structure of the nanoparticles deposited onto an Au-coated Si substrate were also determined.

Production of Small Ag-Containing C60 Nanoparticles under Atmospheric Condition

Naomi Hashimoto, Haruno Murayama, Hideki Tanaka
Jpn. J. Appl. Phys. 47(2008)4777

Ag-containing C60 nanoparticles were produced from Ag vapor interacting with C60 nanoparticles formed by C60 vapor. The particle diameter of the produced nanoparticles was measured using a differential mobility analyzer (DMA). The particle diameter dependence on the Ag vapor temperature was also measured using the DMA. The chemical composition of the produced nanoparticles was investigated by X-ray photoelectron spectroscopy. The experimental results indicated that the C60 nanoparticles worked prominently as a supporting nanomaterial for the Ag nanoparticles.