Symmetry Breaking Induced by Growth Kinetics: One‐Pot Synthesis of Janus Au−AgBr Nanoparticles

Abstract This study describes a one‐pot synthetic strategy consisting of concerted stabilization and photo and chemical reductions of metal ions to yield precise anisotropic nanostructures. Photoirradiation of an aqueous precursor solution containing Au³⁺, Ag⁺, Br⁻, and polyvinylpyrrolidone (PVP) forms Janus nanoparticles (NPs) composed of Au having a tiny Ag shell and AgBr. The Au NPs are initially generated by photoreduction of Au³⁺ in the precursor solution, in which the formation of silver halides is strongly inhibited by the coordination bond between Ag⁺ and the carbonyl groups in PVP. The coordinated PVP chains are adsorbed on the surfaces of the Au NPs, with the concomitant release of free Ag⁺ ions. The part of the surface of the Au NP is covered with a few Ag atoms via chemical reduction of Ag⁺ by PVP. AgBr nanocrystals grow at a bare site on the surface of each Au NP, resulting in the formation of nearly monodisperse Janus Au−AgBr NPs in high yield. A characteristic light absorption profile emerges due to the interface formed between Au and AgBr, which is demonstrated by finite‐difference time‐domain simulation. The precise nanostructures may be leveraged to elucidate mechanisms of photoelectrochemical processes and to construct advanced plasmonic photocatalysts.