The future of lab-on-a-chip devices for the synthesis of nanomaterials hinges on the successful development of high-throughput methods with better control over their size. While significant effort in this direction mainly focuses on developing "difficult to fabricate" complex microfluidic reactors, scant attention has been paid to the "easy to fabricate" and simple millifluidic systems that could provide the required control as well as high throughput. By utilizing numerical simulation of fluids within the millifluidic space at different flow rates, the results presented here show velocity profiles and residence time distributions similar to the case of microfluidics. By significantly reducing the residence time and residence time distribution, a continuous flow synthesis of ultrasmall copper nanoclusters (UCNCs) with exceptional colloidal stability is achieved. In-situ synchrotron-radiation-based X-ray absorption spectroscopy (XAS) reveal that the as-prepared clusters are about 1 nm, which is further supported by transmission electron microscopy and UV-vis spectroscopy studies. The clusters reported here are the smallest ever produced using a lab-on-a-chip platform. When supported on silica, they are found to efficiently catalyze C-H oxidation reactions, hitherto unknown to be catalyzed by Cu. This work suggests that a millifluidic platform can be an inexpensive, versatile, easy-to-use, and powerful tool for nanoparticle synthesis in general, and more specifically for ultrasmall nanoclusters (UNCs). The concept of a millifluidic platform as a promising tool for future lab-on-a-chip devices for a controlled and high-throughput synthesis of ultrasmall nanoclusters (UNCs) is presented, both generally and using copper catalysts as a model. The millifluidic platform is versatile, easy to implement, and low cost; and lithography is not required for its fabrication. It is also a potential tool for carrying out time-resolved in situ analysis as larger dimensions for probing will provide a better signal-to-noise ratio.
- C-H oxidation
- X-ray absorption spectroscopy
- ultrasmall nanoclusters