Production of hydrogen peroxide enabled by microdroplets

Geometry and dimensionality of a reaction system are known to play an important role in determining the yield as well as the rate of the reaction, especially in simple bimolecular reactions (1⇓⇓⇓⇓⇓⇓–8). Recently, several results have been reported for reactions in small droplets, which include charged microdroplets (3), microdiameter emulsions (2), inverted micelles (4), and the surfaces of aerosol particles (1). It has been found that chemical reactions can be accelerated in water microdroplets (2, 3, 6, 7), which indicates that the surface of aqueous microdroplets provides a unique reaction environment with different thermodynamics and kinetic properties compared to the bulk phase. In PNAS, Lee et al. (8) report experimental evidence that hydrogen peroxide (H2O2) is spontaneously produced from pure water by atomizing bulk water into microdroplets, which does not occur in bulk aqueous solutions. Production of H2O2 increases with decreasing microdroplet size, and the generated H2O2 concentration is ∼30 µM. Further analysis suggests that hydroxyl radical (OH) (which is generated by loss of an electron from OH− near the surface of the water microdroplet) recombination is the most likely source. H2O2 is a very simple compound in nature but with great importance in clinical, pharmaceutical, textile, environmental, and food manufacturing applications. One of the most important applications of H2O2 is its use in pulp and paper bleaching (9). It is also a very attractive oxidant for liquid-phase reactions, since H2O2 can oxidize a large variety of inorganic and organic substrates in liquid-phase reactions under very mild reaction conditions. Also, it can be used to improve the environment by oxidative removal of toxic compounds (10). Upon decomposition, H2O … [↵][1]1To whom correspondence may be addressed. Email: frjoseph{at}sas.upenn.edu. [1]: #xref-corresp-1-1