Nanostructured TiO2 as a sonophotocatalytic cavitation agent for spatially controlled sonochemistry

Abstract

Sonochemistry has garnered interest in its ability to facilitate greener chemistry by minimizing the use of hazardous reagents and harsh reaction conditions commonly used in chemical synthesis. The operating principle for sonochemistry is inertial cavitation, whereby bubble collapse will induce water pyrolysis to generate radicals for use in chemical reactions. Unfortunately, this process is limited by the low efficiencies in converting electrical energy to cavitation energy for free radical generation. To remedy this, researchers have exploited phenomena, e.g., sonoluminescence, using heterogenous catalysts to increase the radical generation rate; however, the stochastic nature of cavitation requires prolonged periods of high intensity, continuous wave irradiation to generate sufficient reaction rates. To address these limitations, we nanostructured TiO2 to function as sonophotocatalytic cavitation agents (SCAs). Our SCAs demonstrate that sonoluminescence can more efficiently occur at the catalyst surface and at lower energies using pulsed ultrasound. We evaluated the functionality of our SCAs by benzyl alcohol oxidation to benzaldehyde, where we further modified the catalysts using AuPd nanoparticles to function as a co-catalyst for enhanced sonoreactivity. Our findings present the key design elements for developing an effective SCA, allowing future work to explore the versatility of SCAs for a wide range of chemical applications.