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 ¹⁹F 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