Silver‐Mediated Squaric Acid Reduction as a Facile, Ambient‐temperature and Seedless Route to Tunable Bimetallic Au/Ag Nanostars and Nanosnowflakes

Abstract Bimetallic Au/Ag nanoparticles were successfully synthesized using a facile and reproducible method involving rapid, room‐temperature mixing of aqueous solutions of HAuCl₄ and AgNO₃ in the presence of squaric acid as both the reducing agent and surface capping ligand. Variation in the initial Au : Ag molar ratio yielded a tunable anisotropic shape and affiliated surface plasmon resonance. The nanoparticles displayed excellent stability in water for at least 10 weeks and showed robust catalytic activity in the borohydride‐assisted reduction of the model substrate 4‐nitrophenol.