Controllable incorporation of Ag and Ag–Au nanoparticles in carbon spheres for tunable optical and catalytic properties

Abstract

Spherical Ag–C composites containing Ag nanoparticles (NPs) have been synthesized in high yield by microwaving suspensions of porous carbon spheres (CSs) in [Ag(NH₃)₂]⁺ solutions with poly (N-vinylpyrrolidone) as the reducing agent. The use of Ag–C composites as precursors enables us to dope Au also into the CSs' interior. Various Ag–Au doped and also predominantly Au composite spheres are prepared via the immersion of the Ag–C composites in chloroauric acid (HAuCl₄) solutions without additional reducing agent. The yield of Au is found to be much higher than a replacement reaction could provide, which is explained via a detailed discussion of the involved growth mechanisms that decide the locations of the NPs in/on the CSs. Optical properties and catalytic activities of the composite structures are tunable via the Au versus Ag atomic ratio as controlled by the HAuCl₄ concentration. The composites exhibit excellent catalytic activity as demonstrated via the reduction of 4-nitrophenol by sodium borohydride. The catalytic activity of bimetallic composites is highly enhanced over the monometallically doped CSs.