The effect of porosity and particle size on the kinetics of porous carbon xerogels surface oxidation

Abstract

Carbon surface oxidation was investigated to assess the effects of porosity and particle size on its course. Carbon xerogels that differed in porosity (micro-, micro-meso-, and micro-meso-macroporous materials) and particle size (from fine powders to monolithic cubes) were prepared. The prepared materials were characterized in detail with nitrogen sorption, SEM, and HRTEM. The oxidation of carbon xerogels was studied by isothermal thermogravimetry (TG) in an oxidizing atmosphere (50% O2 and 50% Ar). Isothermal TG experiments showed that the effects of particle size and porosity are interrelated and should be evaluated together as both significantly influence diffusion and heat transfer during carbon oxidation. On the basis of isothermal TG data, apparent kinetic parameters were determined assuming that carbon burn-off, the creation of oxygen surface groups, and the decomposition of created oxygen surface groups are reactions controlling the carbon surface oxidation. Detailed analysis of the obtained parameters proved that porosity and particle size do not affect the basic chemical reactions that occur on the carbon surface during oxidation.