Free radicals and graphite

Abstract

The basal faces of crystalline graphite do not react with molecular oxygen at ambient or moderately raised temperatures. Free radicals, however, react with exposed graphene layers of graphites and carbon materials. Such reactions can be exploited for the functionalization of carbon surfaces. Disordered carbons, e.g. activated carbons, are slowly oxidized also at room temperature when water vapor is present. Surface oxides are formed, and some CO2 is gradually released in this aging reaction. It was found that nitrogen doping of carbons accelerates considerably their aging and increases also their catalytic activity in other oxidation reactions with O2. Evidence is presented that this activation of O2 molecules is due to transfer of electrons from the N-doped carbons to adsorbed O2. The electrons come from nitrogen atoms bound substitutionally in the graphene layers. Superoxide ions, O2-, are created that react with water producing hydroxyl radicals, OH