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The wide-scale production of nanomaterials would benefit from scalable synthetic methods. One class of promising nanomaterials consists of a core@shell structure in which one type of material is used for the core and a second material is grown on the surface to produce a shell. Although these materials are commonly realized in batch, core@shell structures have not yet been widely translated to scalable manufacturing processes. In this work, we investigate the continuous flow synthesis of Au@Ag core@shell nanomaterials using sequential jet-mixing reactors (JMRs). Connecting the two JMRs overcomes challenges with particle instability when the processes are separated. Using synthesis conditions typical for batch methods in the JMR resulted in a non-uniform particle size distribution. Through investigating the synthesis conditions of the Au core, the key parameters affecting the synthesis of well-defined nanoparticles are identified as the concentration of the reducing agent and the inclusion of bovine-serum albumin (BSA) to limit particle aggregation. The concentration of the reducing agent is adjusted to achieve a high yield of Au NPs. The adjusted concentration enabled continuous synthesis of Au@Ag core@shell nanoparticles using BSA as the stabilizing ligand in a dual jet mixing reactor system. Overall, this work provides insights on integrating sequential processes for the synthesis of core@shell nanomaterials. 

Commonly used batch reactors for nanomaterial synthesis can be difficult to scale since rapid particle nucleation and growth require efficient mixing to produce monodisperse particle size distributions (PSD). Monodisperse particles can be synthesized through efficiently mixing the reactants in the liquid phase using a jet-mixing reactor. Using common synthesis precursors and concentrations, the jet-mixing reactor produces silver nanoparticles with a diameter of 5 ± 2 nm, as characterized by TEM, and a monomodal surface plasmon resonance (SPR) in the UV-vis spectrum. In comparison, a batch synthesis using the same concentrations of reactants produces nanoparticles with a diameter of 9 ± 4 nm and a bimodal SPR, indicating that jet-mixing produces a more monodisperse particle size distribution than batch synthesis. For the jet-mixing synthesis, the concentration of the capping agent can be reduced to a value of 0.05 mM while retaining a narrow full-width of half-maximum (FWHM) of the SPR spectrum. Interestingly, decreasing the capping agent quantity from the standard concentration of 0.2 mM to 0.05 mM decreases the FWHM of the SPR, corresponding to a more monodisperse PSD at lower capping agent concentration. This result is attributed to the increased stabilization at lower ion concentrations in the solution. For low capping agent concentrations, additional experiments adding small amounts of sodium nitrate support this observation. Overall, the jet-mixing reactor represents a viable system for the continuous production of size-controlled silver nanoparticles with reduced amounts of capping agent.