Preparing Alumina-Supported Gold Nanowires for Alcohol Oxidation

Abstract

The development of shape-controlled noble metal nanocrystals such as nanowires (NWs) is progressing steadily owing to their potentially novel catalytic properties and the ease with which they can be prepared by reducing the metal ions in a particular solution as capping agents. Recently, many reports have been presented on the preparation of shape-controlled Au nanocrystals, such as nanostars and nanoflowers, by a one-pot method using 2-[4-(2-hydroxyethyl)-1-piperazinyl] ethanesulfonic acid (HEPES) as capping and reducing agents. The catalytic activity is depressed due to the adsorption of the capping agent onto a Au surface. Since HEPES has low binding affinities on the Au surface, shape-controlled nanocrystals obtained using HEPES are effective for application as nanocatalysts because HEPES was easily removed from the Au surface. In this study, we report the preparation of AuNWs, with an average diameter of 7.7 nm and lengths of a few hundred nanometers, in an aqueous solution containing HEPES and sodium borohydride. A γ-Al 2 O 3 -supported AuNW (AuNW/γ-Al 2 O 3 ) catalyst was obtained using catalytic supporters and a water extraction method that removed HEPES from the Au surface without morphological changes. AuNW/γ-Al 2 O 3 was then utilized to catalyze the oxidation of 1-phenylethyl alcohol to acetophenone. The formation rate of acetophenone over AuNW/γ-Al 2 O 3 was 3.2 times that over γ-Al 2 O 3 -supported spherical Au nanoparticles (AuNP/γ-Al 2 O 3 ) with almost the same diameter.

Au Nanoparticle Monolayer Nanosheets as Flexible Transparent Conductive Electrodes

“…The UVirradiated nanosheets were confirmed to be crystalline gold by measuring their XRD patterns, as shown in Figure 4a, in which the reflection peaks at 38.1°, 44.2°, 64.6°, and 77.6°were assigned to the (111), ( 200), (220), and (311) crystal facets of Au with a face-centered cubic structure, respectively. 35,36 Further, the HR-TEM image of the Au nanosheet (Figure 4b) exhibited 0.235 nm periodic fringes of Au (111) crystal facets in different directions, 36 indicating that the Au nanosheets consisted of polycrystalline domains. The fusion of AuNPs was attributed to the decomposition of DODAC adsorbed on the AuNPs induced by the UV light, 24 as confirmed by the FTIR spectra of the AuNP monolayers at various UV irradiation times (Figure 5).…”

Conductive Nanosheets Fabricated from Au Nanoparticles on Aqueous Metal Solutions under UV Irradiation

“…Figure 5 shows the XRD pattern of a nanosheet prepared on a 480 µM HAuCl 4 solution. The nanosheet was confirmed as crystalline gold, based on reflection peaks at 38.2 • , 44.3 • , 64.5 • , 77.5 • , and 81.7 • , which were assigned to the (111), ( 200), ( 220), (311), and (222) crystal facets of Au, respectively, with a face-centered cubic structure [32,33]. Electrical resistances of Au nanosheets prepared on water, 4.8 µM, 48 µM, and 480 µM HAuCl 4 solutions were 2600 Ω/sq, 2220 Ω/sq, 6.5 Ω/sq, and 4.1 Ω/sq, respectively.…”

“…Further, we measured the XRD pattern of the hybrid nanosheet to determine whether silver is oxidized or whether AgNO 3 deposits directly on the nanosheet, although distinguishing between metallic Au and Ag from XRD diffraction is difficult because these metals have nearly identical lattice constants [36]. The XRD pattern in Figure 9a showed reflection peaks at 38.2 • , 44.0 • , 64.3 • , and 77.3 • , assigned to the (111), ( 200), (220), and (311) crystal facets of metallic Ag and/or Au, respectively [32,33,37,38]. The absence of silver oxide and AgNO 3 peaks suggested that the hybrid nanosheet was composed of metallic Ag and Au [39,40].…”

Recent advances in nanoflowers: compositional and structural diversification for potential applications

“…Imura et al reported the preparation of bimetallic Au-Ag nanoowers by reducing HAuCl 4 in a solution containing melamine (as the capping agent) and ascorbic acid (as the reducing agent), which are weakly adsorbed on the surface of the metal. 342 Bimetallic Au-Ag nanoowers are obtained with a clean surface using a support (g-Al 2 O 3 ) 38,[343][344][345][346][347] and an extracting method (extracting the surface ligands with water). 348,349 A weakly adsorbing capping agent, adequate washing processes to remove capping agents from the metal surface, and a supporting method to inhibit aggregation are vital factors in obtaining surface-clean Au nanoowers.…”