Fig. 1. Typical TEM and SAED images of Au₁Ag₁ ANPs

Fig. 2. Elemental mapping image of a single Au₃Ag₁ ANP

Fig. 3. Absorption spectra of Ag NPs，Au₁Ag₃ ANPs，Au₁Ag₁ ANPs，Au₃Ag₁ ANPs，and Au NPs，insets are the synthesized samples photographs of five noble metal nanomaterials from left to right

Fig. 4. Extinction spectra of Ag NPs，Au₁Ag₃ ANPs，Au₁Ag₁ ANPs，Au₃Ag₁ ANPs，and Au NPs，which correspond to black，green，red，blue and yellow curves

Fig. 5. A tentative mechanism of the chemical reduction of 4-NTP by NaBH₄ catalyzed by the noble metal NPs

Fig. 6. The variation of 4-NP concentration in the noble NPs with different reduction times