pH-induced recovery and redispersion of shape-controlled gold nanorods for nanocatalysis

Morita-Imura, Clara; Kobayashi, Takaaki; Imura, Yoshiro; Kawai, Takeshi; Shindo, Hitoshi

doi:10.1039/c5ra17369h

Cited by 17 publications

(28 citation statements)

References 53 publications

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13] The properties of a metal NC are dependento ni ts morphology, including size and shape. [1][2][3][4][5][6] Therefore, many methods for the preparation of NCs with various shapes, such as nanoflowers, [14][15][16][17] nanocubes, [18][19][20][21] nanorods, [22][23][24] and nanowires, [25][26][27][28][29][30][31] with the desired properties have been reported. In general, these shape-controlled NCs are prepared by colloidal syntheses in as olution using capping agents that selectively adsorb to the metal surface.…”

Section: Introductionmentioning

confidence: 99%

Au–Ag Nanoflower Catalysts with Clean Surfaces for Alcohol Oxidation

Imura

Akiyama

Furukawa

et al. 2019

Chemistry An Asian Journal

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Shape‐controlled metal nanocrystals, such as nanowires and nanoflowers, are attractive owing to their potentially novel catalytic properties and bimetallic nanocrystals composed of two distinct metals are expected to act as highly active catalysts. However, their catalytic activities are limited because of the capping agents adsorbed on the metal surfaces, which are necessary for the preparation and dispersion of these nanocrystals in solvents. Therefore, the preparation of bimetallic shape‐controlled noble metal nanocrystals with clean surfaces, devoid of almost all capping agents, are expected to have high catalytic activity. Herein, we report the preparation of bimetallic Au–Ag nanoflowers using melamine as the capping agent. The bimetallic Au–Ag nanoflowers with a clean surface were subsequently obtained by a support and extraction method. The bimetallic nanoflowers with a clean surface were then used for the aerobic oxidation of 1‐phenylethyl alcohol and they exhibited high rates for the formation of acetophenone compared to Au nanoflowers and spherical nanoparticles with almost the same size and Au/Ag ratio. We also show that Au–Ag nanoflowers containing only 1 % Ag (Au99–Ag1NFs) exhibit the highest rate of acetophenone formation among Au–Ag nanoflowers with different Au/Ag ratios owing to an increase in the electron density of the Au atoms that act as active sites for the oxidation of 1‐phenylethyl alcohol.

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Section: Introductionmentioning

confidence: 99%

Au–Ag Nanoflower Catalysts with Clean Surfaces for Alcohol Oxidation

Imura

Akiyama

Furukawa

et al. 2019

Chemistry An Asian Journal

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“…28,29 The lamellar supramolecules of C16CA have been found to incorporate gold nanocrystals with a spherical or rod-like morphology due to the adsorption of the amphiphile on the metal surface. Carboxyl and amine groups also adsorb onto silver surfaces 32,33 such as amino acid or DNA.…”

Section: ■ Introductionmentioning

confidence: 99%

Stimuli-Responsive Extraction and Ambidextrous Redispersion of Zwitterionic Amphiphile-Capped Silver Nanoparticles

et al. 2016

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Citrate-stabilized silver nanoparticles (AgNPs) were functionalized with a pH-responsive amphiphile, 3-[(2-carboxy-ethyl)-hexadecyl-amino]-propionic acid (C16CA). At pH ∼ 4, the zwitterionic C16CA assembled into lamellar structures due to the protonation of the amine groups of the amphiphile that neutralized the anionic charge of the carboxylate groups. The lamellar supramolecules incorporated the AgNPs into their 3D network and extracted them from water. C16CA supramolecules dissolved into water (at pH > 6) and organic solvents; consequently, the recovered C16CA-AgNPs were redispersed not only to water but also to chloroform and tetrahydrofuran without any additional functionalization. C16CA acted as a pH-responsive stabilizer of AgNPs and formed a solvent-switchable molecular layer such as a bilayered structure in water and densely packed monolayer in chloroform and tetrahydrofuran. Redispersion of the AgNPs was achieved in different solvents by changing the solvent affinity of the adsorbed C16CA molecular layer based on the protonation of the amine groups of the pH-responsive amphiphile. The morphology of redispersed AgNPs did not change during the recovery and redispersion procedure, due to the high steric effect of the network structure of C16CA supramolecules. These observations can lead to a novel solvent-exchange method for nanocrystals without aggregation and loss of nanocrystals, and they enable effective preparations of stimuli-responsive plasmonic nanomaterials.

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“…Over the past few decades, the continuous development of new routes for the synthesis of NCs has resulted in the availability of NCs with desired sizes, size distributions, shapes and compositions . Recently, the preparation and application of NCs that respond to external stimuli, such as light, temperature and pH, have become attractive . It is known that external‐stimuli‐responsive NCs are applied in sensors, photochromic paper, and novel NC recovery systems .…”

Section: Introductionmentioning

confidence: 99%

“…Recently, the preparation and application of NCs that respond to external stimuli, such as light, temperature and pH, have become attractive . It is known that external‐stimuli‐responsive NCs are applied in sensors, photochromic paper, and novel NC recovery systems . External‐stimuli‐responsive NCs have often been prepared using capping agents that respond to external stimuli .…”

Section: Introductionmentioning

confidence: 99%

“…It is known that external‐stimuli‐responsive NCs are applied in sensors, photochromic paper, and novel NC recovery systems . External‐stimuli‐responsive NCs have often been prepared using capping agents that respond to external stimuli . However, the external‐stimuli‐responsive capping agent can only be used to prepare specific external‐stimuli‐responsive metal NCs due to the low stability of metal NCs.…”

Section: Introductionmentioning

confidence: 99%

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pH‐Responsive Supported and Unsupported Gold Nanocrystals

Imura

Morita-Imura

et al. 2017

ChemistrySelect

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The pH-responsive zwitterionic amphiphile (C18Tyr) was used for the functionalization of unsupported Au nanocrystals, a SiO 2 support, and SiO 2 -supported Au nanocrystals in a biphasic water/chloroform system, for useful supported nanomaterials. The solubility of C18Tyr was controlled by adjusting the pH of the water/chloroform system; at pH 8.0 and 3.5, almost all of the C18Tyr dissolved in the water and chloroform phases, respectively. This pH-dependent solubility control is due to protonation/deprotonation of the amino and carboxyl groups of C18Tyr. The unsupported Au nanocrystals in C18Tyr/water/ chloroform were reversibly transferred between the water and chloroform phases by pH control, but the phase transfer yield was low due to the aggregation and deposition of Au nanocrystals. Therefore, we prepared pH-responsive supported nanocrystals, as they are known to have high stabilities compared to unsupported nanocrystals. The SiO 2 support, without Au nanocrystals, was reversibly dispersed and precipitated in the C18Tyr/water/chloroform system by pH control, and not reversibly transferred between the water and chloroform phases. SiO 2 -supported Au nanocrystals were also reversibly dispersed and precipitated as was observed for the SiO 2 support. Therefore, the dispersion-precipitation response of the SiO 2 -supported Au nanocrystals is due to the SiO 2 support, not the Au nanocrystals. Furthermore, no loss of Au nanocrystals was observed due to the improved stability of the Au nanocrystals supported by this method. These results are very useful for preparation and application of externally responsive supported nanocrystals with high stabilities.

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pH-induced recovery and redispersion of shape-controlled gold nanorods for nanocatalysis

Abstract: The pH-responsive amphiphile C16CA was used for the functionalization of gold nanorods. The pH-induced recovery–redispersion of gold nanorods using C16CA self-assembly was accomplished without affecting the catalytic activity of the nanorods.

Cited by 17 publications

References 53 publications

Au–Ag Nanoflower Catalysts with Clean Surfaces for Alcohol Oxidation

Au–Ag Nanoflower Catalysts with Clean Surfaces for Alcohol Oxidation

Stimuli-Responsive Extraction and Ambidextrous Redispersion of Zwitterionic Amphiphile-Capped Silver Nanoparticles

pH‐Responsive Supported and Unsupported Gold Nanocrystals

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