Syntheses, Plasmonic Properties, and Catalytic Applications of Ag-Rh Core-Frame Nanocubes and Rh Nanoboxes with Highly Porous Walls

We report a simple and general method for the production of Ag-Rh bimetallic nanostructures with a unique integration of the plasmonic and catalytic properties exemplified by these two metals, respectively. When a Rh(III) precursor is titrated into a polyol suspension of Ag nanocubes held at 110 °C in the presence of ascorbic acid and poly(vinylpyrrolidone), Rh atoms are generated and deposited on the nanocubes. When the amount of Rh(III) precursor is relatively low, the Rh atoms tend to nucleate from the edges of the Ag nanocubes and then follow an island growth mode because of the relatively low temperature involved and the high cohesive energy of Rh. The Rh islands can be maintained with an ultrafine size of only several nanometers, presenting an extremely large specific surface area for catalytic applications. As the amount of Rh(III) precursor is increased, the galvanic replacement reaction between the Rh(III) and Ag nanocubes will kick in, leading to the formation of increasingly concaved side faces and an increase in surface coverage for the Rh islands. Meanwhile, the resultant Ag⁺ ions are reduced and deposited back onto the nanocubes, but among the Rh islands. By simply controlling the amount of Rh(III) precursor, we observe the transformation of Ag nanocubes into Ag-Rh core-frame and then Ag-Rh hollow nanocubes with a highly porous surface. Upon selective removal of Ag by wet etching, the hollow nanocubes evolve into Ag-Rh and then Rh nanoboxes with highly porous walls. Although the Ag-Rh core-frame nanocubes show a unique integration of the plasmonic and catalytic properties characteristic of Ag and Rh, respectively, the Rh nanoboxes show remarkable activity toward the catalytic degradation of environmental pollutants such as organic dyes.