The Effects of Concentration Intensification on Nanoparticle Synthesis

Abstract

Realizing the promise of nanoparticle-based technologies demands more efficient, robust synthesis methods (i.e., process intensification) that consistently produce high-quality and large-quantities of nanoparticles (NPs). We explored NP synthesis via the heat-up method in a regime of previously unexplored high concentrations near the solubility limit of the precursors. We discovered that in this highly concentrated and viscous regime the NP synthesis parameters are less sensitive to experimental variability and thereby provide a robust, scalable, and sizefocusing NP synthesis. Specifically, we synthesize high-quality metal sulfide NPs (< 7% relative standard deviation for Cu2-xS, CdS, and PbS), and demonstrate 10-1000 fold increase in Cu2-xS NP production (>200 g) relative to the current field of large-scale (0.1-5 g yields) and lab-scale (<0.1 g) efforts. Compared to conventional synthesis methods (hot-injection with dilute precursor concentration) characterized by rapid growth and low yield, our highly concentrated NP system supplies remarkably controlled growth rates and a ten-fold increase in NP volumetric production capacity (86 g/L). The controlled growth, high yield, and robust nature of highly concentrated solutions can facilitate large-scale nano-manufacturing of NPs by relaxing synthesis requirements to achieve monodisperse products. Mechanistically, our investigation of the thermal and rheological properties, and growth rates reveals that this high concentration regime has an order of magnitude increase in solution viscosity, reducing mass diffusion, a ~67% increase in heat capacity, stabilizing the reaction to perturbations, and the decreasing influence of Ostwald ripening.