Dissolved Oxygen Redox as the Source of Hydrogen Peroxide and Hydroxyl Radical in Sonicated Emulsive Water Microdroplets
Abdelilah Asserghine, Aravind Baby, Jeanne N’Diaye, Adolfo I. B. Romo, Supriya Das, Chloe A. Litts, Prashant K. Jain, Joaquín Rodríguez‐López
Abstract
High Resolution Image Download MS PowerPoint Slide Sonicated emulsive water microdroplets (SEWMs) accelerate and enable a variety of catalyst-free chemical transformations. However, significant unanswered questions remain regarding the chemical intermediates they form and their possible redox origin. In this study, we identified dissolved O 2 as the primary originator of reactive oxygen species (ROS) such as OH • and H 2 O 2 . We uncovered the role of dissolved O 2 redox by using a combination of microelectrochemical methods to detect H 2 O 2, isotopic methods to identify the source of H 2 O 2, and a combination of electron spin resonance and the DMPO spin trap to detect radicals such as OH • . Notably, we found that H 2 O 2 production is correlated with O 2 content via a reduction pathway enabled by a sufficiently large reducing power that can additionally generate H 2 and even perform Pb electroless deposition on Au and Cu metal substrates. Building on our findings, continuous O 2 bubbling of SEWMs showed accumulation of H 2 O 2 up to ∼88 mM in the aqueous phase within 1 h of sonication, demonstrating the scale-up promise of this method. Distinct to sonochemistry of a single phase, this study advances our understanding of the confluence of redox and chemical reaction mechanisms within SEWMs as a biphasic system. This insight paves the way for improving their reaction kinetics, yield, and selectivity, positioning these attractive redox microreactors as alternatives to traditional electrolyzers.