Sizing the ozone Fenton reaction pathways: Ferryl vs hydroxyl

Abstract

Ozone Fenton chem. between a ferrous ion (Fe²⁺) and ozone (O₃) produces ferryl ion (Fe(IV)O²⁺) through O-atom transfer and hydroxyl radical (.OH) through single-electron transfer reaction, and so far the two products have been studied sep. This work investigates their relative importance using di-Me sulfoxide (Me₂S=O, DMSO) as a representative org. substrate and online/offline electrospray mass-spectrometry (ESI-MS) as the anal. technique. Ozone-Fenton reaction occurs at the interface of an aq. DMSO/Fe²⁺ jet and an intersecting O₃ stream in online ESI-MS, and in the bulk aq. phase of a converging stream of DMSO/Fe²⁺ soln. and O₃ soln. in offline ESI-MS. We measure the ratio of ferrylproducts : hydroxyl-products to be 300-1600 at air-water interface, at 10⁵ faster rate than in bulk. The presence of ligands expands the range of ratio to 100-8000 while increasing the overall yield by up to a factor of 4. The ferryl ion in all tested conditions play a more important role than hydroxyl radical in ozone Fenton chem. in acidic aq. medium, a typical condition in atm. aerosols.