A significant barrier to the deployment of sustainable carbon utilization chemistries—including biofuel production and CO2 capture and conversion—is the high cost of catalyst materials. While nanoparticle catalysts promise a more efficient use of raw catalyst materials due to their high surface area-to-mass ratio and enhanced activity, current approaches to manufacturing them are small-scale, and standard scale-up strategies sacrifice the particle quality that is necessary for effective catalysts.
One promising approach to scaling catalytic nanoparticle manufacturing is to adapt microfluidic techniques to industrial processes. Microfluidic channels can maintain the uniform local concentration and thermal conditions necessary for high-quality nanoparticle growth. Over the past several years, Malmstadt has developed techniques to increase the throughput of continuous flow microfluidic reactors to an industrially relevant scale. These efforts include surface and geometry control to maximize flow rates, channel scaling from the microfluidic to the millifluidic, and large-scale reactor parallelization.
Malmstadt has used microfluidic channels with tailored surface energies to widen the range of flow rates in which stable droplet formation is possible, allowing for the throughput of a reactor for producing gold and silver nanoparticles to be increased orders of magnitude. Similarly, new 3D geometries for droplet formation allow for flow stability across a network of parallel reactors synthesizing platinum nanoparticles. This enabling technology for parallelization was adapted to a large-scale parallel reactor, in which 16 channels synthesized CsPbBr3 quantum dots under the guidance of a real-time optimization algorithm that used in situ monitoring to guarantee uniform particle sizes across the network. This parallel network can process on the order of 1 L/h of reagent, an industrially relevant throughput.
These scaling approaches have been coupled with tools from green chemistry to design sustainable synthesis approaches. In particular, Malmstadt has pioneered the use of ionic liquids as solvents for the in-flow synthesis of nanoparticles and has recently demonstrated that design-of-experiments and in situ optimization approaches can be used to locate operating points for in-flow solvent recycling.
Together, this suite of technologies represents a promising route to the green synthesis of next-generation catalysts needed for a range of sustainable energy applications.
Noah Malmstadt is a professor of chemical engineering and materials science, chemistry, and biomedical engineering at the University of Southern California, where he also serves as associate chair of the Mork Family Department of Chemical Engineering & Materials Science. He earned his BS in chemical engineering from Caltech and a Ph.D. in bioengineering from the University of Washington. After a postdoctoral fellowship at UCLA, he joined the USC faculty in 2017. Malmstadt is the recipient of an ONR Young Investigator award, a Charles Lee Powell Foundation research award, and a Journal of Laboratory Automation JALA Ten award. He is a senior member of the National Academy of Inventors. Malmstadt’s work focuses on engineered interfaces for applications spanning nanomaterials synthesis, medical diagnostics, and cell membrane biophysics. His research group pioneered the application of 3D printing techniques to microfluidic device manufacturing and has led the development of sustainable chemistry practices for manufacturing nanomaterials.