Synthesizing Colloidal Bimetallic Nanoparticles in Water Using a Dual-Ligand Strategy

Controlled aqueous synthesis of bimetallic nanoparticles below 5 nm remains challenging due to reduction potential mismatches between noble and base metals, which often causes uncontrolled aggregation. Here, we propose a dual-ligand strategy to assist the commonly used seed-mediated method in aqueous phase to demonstrate fine control for the formation of uniform bimetallic nanoparticles. To decouple reduction kinetics and colloidal stabilization, polyvinylpyrrolidone (PVP) was used as a steric stabilizer for the preparation of the seeds, and polyethyleneimine (PEI) as a strong chelating agent to strictly regulate base metal reduction on the surface of seeds. This strategy allows controlled deposition and pairing of noble metal seeds (e.g., Pt, Pd, and Rh) with base metals (e.g., Cu, Ni, Co, and Fe) with a tunable atomic ratio from 3:1 to 1:2. Furthermore, we demonstrate that this synthetic platform can be extended to trimetallic compositions (such as Pt/Cu/Co and Pt/Cu/Ni). To demonstrate the utility of uniform nanoparticles prepared with this strategy, several bimetallic nanoparticle combinations were evaluated for the catalytic hydrogenation of carbon dioxide (CO₂). Optimizing the metal composition and support materials maximized active Rh sites and Rh─Fe interfaces to enhance ethanol production. This work presents a robust synthetic platform for synthesizing bimetallic nanoparticle catalysts.