Optical and catalytic properties of Au-Ag bimetallic nanocomposites

The gold-silver (Au-Ag) bimetallic nanocomposites were prepared in acid aqueous solution by co-reduction of chloroauric acid and silver nitrate with sodium borohydride in the presence of well-defined diblock copolymer poly(N-isopropylacrylamide)- block -poly(4-vinylpyridine) UV–vis spectroscopy and X-ray diffraction revealed the formed nanocomposites were truly bimetallic nanoparticles rather than the physical mixture of monometallic nanoparticles. The bimetallic nanocomposites showed optical properties corresponding to both their metallic composition and system temperature. The surface plasmon resonance showed a red-shift with increase of the ratio of Au in the nanocomposites, and appeared in their temperature changes. The bimetallic nanocomposites exhibited surface plasmon band corresponding to Au below 4 °C, corresponding to both Au and Ag increasing to 42 °C, and corresponding to Ag above 45 °C. When these bimetallic nanocomposites were applied to catalyze 4-nitrophenol to 4-aminophenol, their catalytic activity first increased and then decreased and finally increased again with the temperature change.