New Sonochemical Methodologies for Nanostructured Materials

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

TECHNICAL SUMMARY: The chemical effects of ultrasound do not come from a direct interaction with molecular species. Instead, sonochemistry arises from acoustic cavitation: the formation, growth, and implosive collapse of bubbles in a liquid. Collapse of bubble clouds produces intense local heating (~5000 K), high pressures (~1000 atm), enormous heating/cooling rates, all in isolated sub-micron reactors. Cavitation thus represents a unique interaction of energy and matter and provides access to a distinct region of reactivity and a general synthetic methodology for the production of unusual materials. The goal of this proposal is to couple a fundamental understanding of the chemical and physical effects of high intensity ultrasound to the development of a new synthetic methodology with diverse applications in the synthesis of nanostructured materials with unusual morphologies and useful chemical properties. Projects will utilize synthetic sonochemical methodologies that fall into three related categories: (1) the direct sonochemical synthesis of novel nanostructured materials; (2) the synthesis of novel nanostructured materials using ultrasonic spray pyrolysis; and (3) the effects of acoustic cavitation on slurries: inter-particle collisions and sonocrystallization. The targets in these three domains include new routes to nanomaterials and nanoporous materials for lithium ion battery anodes, novel fluorescent carbon nanodots, and new morphologically-robust hollow-shell forms of main-group metal oxides for CO2 sequestration. In addition, the fundamental physical phenomena that occur during ultrasonic irradiation of liquid-solid slurries will be explored. Cavitation in slurries generates shockwaves that can drive solid particles together at velocities that approach the speed of sound in the liquid. These interparticle collisions can have dramatic effects on the reactivities of slurried powders. For example, the effect of ultrasound on crystallization will be examined to produce a mechanistic understanding of the phenomena; sonocrystallization which has been empirically used on large scale for preparation of active pharmaceutical ingredients (APIs), but little systematic understanding of its origins is currently available. NON-TECHNICAL SUMMARY: The use of high intensity ultrasound has undergone dramatic growth in materials science during the past decade. As our understanding of the chemical effects of ultrasound has grown, so too has the impact of sonochemistry on a wide range of the physical sciences. Importantly, sonochemistry also has substantial strategic research significance to our industrial economy. Ultrasound already has major industrial applications (e.g., cleaning, welding, emulsification, biotech processing), and the U.S. dominates the world market in production of ultrasonic equipment. Commercial generators of high intensity ultrasound for very large scale liquid processing are available off the shelf, and ultrasonic cleaning is now the standard for both general purpose industrial and microelectronics applications. Thus, the development of sonochemistry and its applications will advance a global market in which the U.S. has a significant commercial advantage. Broader impacts also include the education of the general public about sonochemistry, e.g., through popularized articles which the PI has written for essentially all the general science magazines and major encyclopedias. Finally, substantial success has been made in advanced technical training: over the past five years, 13 Ph.D.'s were graduated, including 4 women and one African-American.