High-Pressure/High-Temperature Microreactors for Nanostructure Synthesis

Chemically synthesized nanomaterials, such as nanocrystalline quantum dots, are being considered as the active element in many applications, including photovoltaics, displays, and biochem sensing. To realize the promise of these devices, it will be critical to have an efficient, reproducible synthesis technique of the nanostructures. Currently, nanoparticles are synthesized in a batch mode in small volumes, which is appropriate for studying the fundamental properties of nanosized structures and for developing proof of principle device structures. However, batch synthesis suffers from control of size, size distribution, and quality of the nanomaterial from batch to batch. Moreover, there is an inherent difficulty in scaling up to quantities more reasonable for device development and optimization. Continuous-flow reactors based on microfluidics (microreactors) integrated with heaters and fluid control elements offer a solution to these problems and additional advantages. We describe continuous synthesis of nanostructures in microfluidic systems consisting of multiple sub-millimeter-sized channels in which fluid flows continuously and chemical reactions take place. The small reaction volumes combined with the high heat and mass transfer rates enable reactions to be performed under more controlled conditions with higher yields than can typically be achieved with conventional reactors. Moreover, manipulation of reaction parameters, while the reaction proceeds, allows optimization of synthesis conditions. The ability to work at elevated temperatures and pressures while confining potentially toxic, high reactive starting materials will become important for the synthesis of novel nanostructured materials. (JALA 2009;14:367-73)