The Spontaneous Electron-Mediated\nRedox Processes\non Sprayed Water Microdroplets

Abstract

Water is considered as an inert environment for the dispersion\nof many chemical systems. However, by simply spraying bulk water into\nmicrosized droplets, the water microdroplets have been shown to possess\na large plethora of unique properties, including the ability to accelerate\nchemical reactions by several orders of magnitude compared to the\nsame reactions in bulk water, and/or to trigger spontaneous reactions\nthat cannot occur in bulk water. A high electric field (∼10⁹ V/m) at the air–water interface of microdroplets has\nbeen postulated to be the probable cause of the unique chemistries.\nThis high field can even oxidize electrons out of hydroxide ions or\nother closed-shell molecules dissolved in water, forming radicals\nand electrons. Subsequently, the electrons can trigger further reduction\nprocesses. In this Perspective, by showing a large number of such\nelectron-mediated redox reactions, and by studying the kinetics of\nthese reactions, we opine that the redox reactions on sprayed water\nmicrodroplets are essentially processes using electrons as the charge\ncarriers. The potential impacts of the redox capability of microdroplets\nare also discussed in a larger context of synthetic chemistry and\natmospheric chemistry.