Room-Temperature\nSynthesis of Au@AuCu Alloyed Nanorods\nin Aqueous Solutions for High Catalytic Activity and Enhanced Stability

Cu-based nanocrystals are desirable for high efficiency\ncatalysis,\nalthough they are easily oxidized under ambient conditions. Alloying\nAu and Cu provides the strategy for Cu-contained nanocrystals toward\nboth high stability and high catalytic activity. However, a synthetic\nmethod of homogeneous alloy nanocrystals with tunable composition\nin aqueous solutions is lacking. Specific composition for achieving\nboth enhanced stability and high catalytic activity remains elusive.\nHerein, coreduction of Au<sup>3+</sup> and Cu<sup>2+</sup> was performed\nthrough controlling the kinetics of the coreduction to form AuCu alloyed\nshells on the Au nanorod (NR) cores and obtain Au@AuCu NRs under the\nprotection of nitrogen. The Cu atomic fraction (atom %) of the shell\nwas finely tuned from 0 to 100% by controlling the fraction of Cu<sup>2+</sup> cations in the growth solution. For Au@Au<sub>0.85</sub>Cu<sub>0.15</sub> NRs, epitaxial growth of AuCu alloy on the Au NR\nwas evidenced with about 4.0% lattice mismatch due to Cu alloying\nin the Au lattice by high-resolution transmission electron microscopy.\nAu@AuCu NRs with different aspect ratios were also obtained for tuning\nlongitudinal plasmonic resonance. Stability characterization indicates\nthat the Au@AuCu NRs with Cu atom % in the shell lower than 15% are\nof enhanced stability, while an increase in Cu atom % in the shell\nfrom 0 to 15.3 and 100% leads to dramatic reduction of the activation\nenergy, <i>E</i><sub>a</sub>, of <i>p</i>-nitroaniline\nfrom 111 to 45 and 33 kJ/mol, respectively. Therefore, Au@Au<sub>0.85</sub>Cu<sub>0.15</sub> NRs are preferable for high catalytic activity\nand enhanced stability.