Mechanism of Hydrogen Peroxide Formation on Sprayed Water Microdroplets.

How is H 2 O 2 formed in sprayed water is not well understood. It is believed to involve the association of HO • radicals spontaneously generated from HO - ions by internal electric fields on the surface of neutral microdroplets. Spraying water actually creates charged microdroplets carrying either excess OH - or H + intrinsic ions that repel each other toward the very surface. The requisite electron transfer (ET) takes place between surface-bound ions: HO S - + H S + = HO S • + H S • , during encounters between positive and negative microdroplets. The ET endothermicity in bulk water (Δ H = 448 kJ mol -1 ) is reversed in low-density surface water by the destabilization of the strongly hydrated reactant ions: Δ H hydration (H + + OH - ) = -1670 kJ mol -1 , relative to neutral radical products: Δ H hydration (HO • + H • ) = -58 kJ mol -1 . The formation of H 2 O 2 is driven by the energy supplied for spraying water, and caused by restricted hydration on microdroplet surfaces.