Interaction of Oxygen with Nanophase Carbons Investigated by Electron Spin Resonance Spectroscopy

Abstract

ABSTRACTInteraction of oxygen with three commercial activated carbons (GX203, P1400 and MEED50 supplied by PICA USA Inc., with BET surface areas of 1000, 1150 and 2000 m2/g respectively) is investigated using 9 GHz electron spin resonance (ESR) spectroscopy. All three carbons give a single ESR line with g = 2.0028(3), but the linewidth ΔH and the spin concentration Ns, are strongly affected by exposure to oxygen. The ESR parameters (g, ΔH, Ns) are measured for different partial pressures of oxygen. For the highly evacuated samples, δH ≃ 1.2 Oe and Ns ≃ 1019/gm and these results are interpreted in terms of uncompensated surface dangling bonds. Oxygen exposure broadens the line and reduces Ns, in direct relation to the surface areas of the carbons and the effect is reversible. Possible effects of the paramagnetic oxygen on dangling bonds are discussed.