Reactivity of wood charcoal with ozone

Abstract

We investigated the resistance of wood charcoal against ozone and estimated the half-life of the charcoal in air. The weight of wood charcoal prepared by the carbonization of Fagus crenata sawdust at 400°C (C-400) was not affected with up to 8.5% ozone while the charcoal prepared at 1000°C (C-1000) burned with 4.9% ozone. Pores with a diameter of approximately 100–200 nm were observed on the surface of ozone-treated C-1000 by scanning electron microscopy, although no pores were found in ozone-treated C-400. The peak positions of the C1s spectra and the full width at half maximum of X-ray photoelectron spectrum peaks suggest that C-400 has an amorphous structure composed of aliphatic carbons and small aromatic molecules while C-1000 and activated charcoal (AC) are polyaromatic. It is likely that the aromatic layers of C-1000 and AC were destroyed and the edge carbon atoms were removed as CO or CO₂ by ozone oxidation. We estimated the half-life of C-1000 with ozone in air to be about 50 000 years by assuming that the weight of C-1000 decayed exponentially. Thus, it is suggested that wood charcoal is stable on a geological time scale.