Room-Temperature Synthesis of Au@AuCu Alloyed Nanorods in Aqueous Solutions for High Catalytic Activity and Enhanced Stability

Abstract

Cu-based nanocrystals are desirable for high efficiency catalysis, although they are easily oxidized under ambient conditions. Alloying Au and Cu provides the strategy for Cu-contained nanocrystals toward both high stability and high catalytic activity. However, a synthetic method of homogeneous alloy nanocrystals with tunable composition in aqueous solutions is lacking. Specific composition for achieving both enhanced stability and high catalytic activity remains elusive. Herein, coreduction of Au³⁺ and Cu²⁺ was performed through controlling the kinetics of the coreduction to form AuCu alloyed shells on the Au nanorod (NR) cores and obtain Au@AuCu NRs under the protection of nitrogen. The Cu atomic fraction (atom %) of the shell was finely tuned from 0 to 100% by controlling the fraction of Cu²⁺ cations in the growth solution. For Au@Au_0.85Cu_0.15 NRs, epitaxial growth of AuCu alloy on the Au NR was evidenced with about 4.0% lattice mismatch due to Cu alloying in the Au lattice by high-resolution transmission electron microscopy. Au@AuCu NRs with different aspect ratios were also obtained for tuning longitudinal plasmonic resonance. Stability characterization indicates that the Au@AuCu NRs with Cu atom % in the shell lower than 15% are of enhanced stability, while an increase in Cu atom % in the shell from 0 to 15.3 and 100% leads to dramatic reduction of the activation energy, E_a, of p-nitroaniline from 111 to 45 and 33 kJ/mol, respectively. Therefore, Au@Au_0.85Cu_0.15 NRs are preferable for high catalytic activity and enhanced stability.