Selective Formation of Hydrogen and Hydroxyl Radicals by Electron Beam Irradiation and Their Reactivity with Perfluorosulfonated Acid Ionomer

Abstract

Selective formation and reactivity of hydrogen (H(•)) and hydroxyl (HO(•)) radicals with perfluorinated sulfonated ionomer membrane, Nafion 211, is described. Selective formation of radicals was achieved by electron beam irradiation of aqueous solutions of H2O2 or H2SO4 to form HO(•) and H(•), respectively, and confirmed by ESR spectroscopy using a spin trap. The structure of Nafion 211 after reaction with H(•) or HO(•) was determined using calibrated (19)F magic angle spinning NMR spectroscopy. Soluble residues of degradation were analyzed by liquid and solid-state NMR. NMR and ATR-FTIR spectroscopy, together with determination of ion exchange capacity, water uptake, proton conductivity, and fluoride ion release, strongly indicate that attack by H(•) occurs at the tertiary carbon C-F bond on both the main and side chain; whereas attack by HO(•) occurs solely on the side chain, specifically, the α-O-C bond.