Boosting energy efficiency and selectivity of glucose oxidation toward glucuronic acid in high-frequency ultrasound using multicavity CuO catalytic cavitation agents

Abstract

Sonochemistry has shown potential to facilitate chemical conversion under near-ambient conditions in water without any chemical additive or other external stimulus. With the help of catalytic cavitation agents, the generation of radicals from ultrasound-induced inertial cavitation can be enhanced and utilized more efficiently for selective chemical transformations. In this study, multicavity CuO (MC-CuO) microparticles were prepared and employed as catalytic cavitation agents to promote spatially selective cavitation and simultaneously catalyze sonochemical oxidation of glucose. Accordingly, the rate of production of OH radicals by sonolysis of water, inferred from titration, was directly related to the cavitation energy, which was determined by analyzing the acoustic signal during pulsed irradiation of 500 kHz ultrasound. Two reaction pathways for glucose oxidation were identified. First, the generation of OH radicals and possibly other reactive oxygen species in the bulk aqueous phase resulted in the formation of gluconic acid, together with other byproducts of C–C bond cleavage and ring opening. Second, the generation of OH radicals in close proximity to CuO resulted in the formation of glucuronic acid with the six membered ring preserved. The present study demonstrates that by appropriately controlling the acoustic parameters (e.g. duty cycle, peak negative pressure and irradiation time) and reaction conditions (e.g. gas atmosphere and the addition of catalytic cavitation agent), it is possible to steer the selectivity of sono-oxidation of glucose towards glucuronic acid, the most value-added product, whilst minimizing the energy input to drive the sonochemical oxidation reaction.