Mark Hersam is a Professor of Materials Science and Engineering at Northwestern University and a MacArthur Foundation "genius" grant winner. He's a pioneer in the area of nanomaterials separations, the processes by which nanomaterials are purified. We chat about the impact of his lab’s breakthrough demonstration of carbon nanotube purification, the perceived value of separations in general, the commercial status of the technology, and the road ahead. (Recorded on September 20, 2016)