Unraveling reaction pathways for tuning bimetallic nanoparticle structures: role of reactant addition sequence

In this work, we experimentally demonstrate the synthesis of different bimetallic Ag–Cu nanostructures like core–shell, Janus particles. It is shown that different nanoparticle structures are associated with different reaction pathways. The pathway is manipulated by modifying the operating conditions (reactant sequence in this case) of the reactions. Ascorbic acid and cetyltrimethylammonium bromide (CTAB) is used as the reducing agent and the capping agent, respectively. Silver nitrate and copper nitrate are used as precursors. The reaction is carried out under microwave-assisted heating, which intensifies metal ion reduction. Two protocols are studied: (I) sequential and (II) simultaneous addition of precursors. By changing the sequence of the precursor addition, the morphology of the bimetallic nanoparticles was altered. Janus particles of size 25–30 nm were formed under the simultaneous addition and the sequential addition when the silver precursor is added first, followed by the copper precursor. When the sequence of precursor addition was reversed, i.e., copper precursor followed by silver, Cu core-Ag shell particles of size 65 nm were formed. We propose mechanisms that help understand the formation of these different structures. Resistance to oxidation studies showed that the particles with Cu core-Ag shell morphology were more resistant to oxidation than Janus particles.