Ionic liquid-directed synthesis of Au–AgBr Janus nanoparticles via digestive ripening and solvated metal atom dispersion†

Multicomponent nanoparticles (MCNs) leverage the synergistic properties of their constituents, offering enhanced performance in diverse applications, including catalysis and photocatalysis. Among them, Janus nanoparticles (JNPs) with their dual domains, stand out as particularly promising. This study presents a novel two-step method to synthesize Au–AgBr JNPs, combining the solvated metal atom dispersion (SMAD) method with digestive ripening (DR). Using ultra-pure metals as precursors negates the need for post-synthesis purification. By adjusting the Au/Ag molar ratio, yields of JNPs up to 85% with precise control of particle size and composition were achieved. The ionic liquid [C₁₈BIm]Br plays a crucial role in promoting AgBr growth on Au nanoparticles, with only low concentrations of ionic liquid favoring Janus structure formation. Additionally, a wet chemical reduction method was also carried out, affording results comparable to those obtained using SMAD and digestive ripening. A mechanistic study for the formation of Au–AgBr JNPs has also been carried out. Driven by a galvanic replacement reaction, the formation mechanism of Au–AgBr JNPs was traced using X-ray photoelectron spectroscopy (XPS). Further, a bromide-free ionic liquid ([C₁₈BIm]NTf₂) was also employed for the synthesis which yields AgAu alloy only and no Janus heterostructure formation.