Au–Ag Nanoflower Catalysts with Clean Surfaces for Alcohol Oxidation

Abstract

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.

Distinctly Different Morphologies of Bimetallic Au-Ag Nanostructures and Their Application in Submicromolar SERS-Detection of Free Base Porphyrin

“…Owing to the similarity of Au and Ag lattice constants (0.408 and 0.409 nm, respectively) [ 17 ], these two noble metals can be easily combined within one nanostructure. It should be noted that the co-reduction of HAuCl 4 and AgNO 3 usually results in nanoalloys (e.g., [ 18 , 19 , 20 ]), although under specific conditions (usage of pomegranate fruit juice as reducing agent and Au(III):Ag(I) molar ratio of 1:1) [ 9 ] Au-Ag core-shell NPs were generated as well.…”

“…From the above mentioned examples, it is obvious that detailed experimental conditions are crucial in the generation of Au-Ag core-shell NSs of different morphologies and varying shell-thicknesses. Until now, several parameters have been thoroughly investigated: various types of additional capping agents on seeds and changes in their concentrations, varying concentrations of Au seeds and AgNO 3 , changes in reaction times and stirring rates [ 11 , 12 , 15 , 20 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ].…”

“…As the second main goal of this work, our attention is devoted to the order of reactants in the second step of seed-mediated growth of the final Au-AgNSs. Usually, the second step of Au-AgNSs generation includes the preparation of a mixture of AgNO 3 and Au seeds (whatever type), followed by the addition of Asc solution, i.e., Asc is added at the end of the seed-mediated growth procedure (e.g., [ 11 , 15 , 20 , 23 , 24 , 28 , 32 , 33 ]). Inspired by the work of Polte et al [ 54 , 55 ], where the principles of metal NPs growth were discussed based on the concept of colloidal stability, we investigated the influence of the reverse order of reactants (i.e., Asc prior to AgNO 3 ).…”

Magnetic Fe3O4-Supported Gold Nanoflowers with Lattice-Selected Surfaces: Preparation and Catalytic Performance

“…Recently, an additional advantage of the ability to efficiently recover the nanocatalysts from the reaction solution, facilitating their repetitive use, was reported. − This recovery of nanocatalysts was successfully accomplished by compounding the magnetic Fe 3 O 4 and spherical noble metal NPs. − There are limited reports on the preparation of shape-controlled NCs with a magnetic response and clean surfaces, as well as on the application of those NCs as nanocatalysts. Previously, we prepared AuNFs supported on γ-Al 2 O 3 with a clean surface under surfactant-free conditions using melamine as the capping agent. − In this paper, we synthesized magnetic Fe 3 O 4 -supported AuNFs and applied them as catalysts for the oxidation reaction of 1-phenylethyl alcohol (1-PA) using air (1 atm) as the oxidant (Figure ).…”

Morphological Stability and Catalytic Performance of Supported and Unsupported Dendritic Gold Nanowire Catalysts

“…The properties of metal nanocrystals are strongly dependent on their size and shape; therefore, an effective synthesis technique is essential to obtain nanocrystals with the desired properties . Recently, there have been many reports on the fabrication of shape‐controlled metal nanocrystals, such as cubes, flowers, rods, and wires . Thermodynamics predicts that noble metal atoms should nucleate and grow into spherical decahedral or icosahedral nanoparticles covered with the (111) crystal facet, because the interfacial free energy (γ) is γ(111) < γ(100) < γ(110) and the surface area per volume of spherical nanoparticles is lower than that of shape‐controlled nanocrystals .…”