Porosity development during steam activation of carbon foams from chemically modified pitch

Microporous carbon foams with high surface areas were obtained by steam activation of foams synthesized from modified pitches by a low pressure foaming process. The choice of the chemical modification of the pitch precursor must be done carefully as it strongly modifies the chemical composition, morphology, structure and reactivity of the resulting carbon foam. [Display omitted] ► Carbon foams from chemically modified pitches are obtained at low pressure. ► The composition of the modified pitch strongly affects the structural features of the foams. ► Sulfuric acid rendered dense and structurally organized foams. ► Narrow microporosity was created during the foaming of nitric acid modified pitches. ► Microporous carbon foams with high surface area were obtained by steam activation. The steam activation of carbon foams obtained after thermo-oxidation treatment of coal tar pitch using inorganic acids (H2SO4 and HNO3), and subsequent low pressure foaming process without stabilization step, was investigated. The characterization of the activated carbon foams showed a strong dependence of the final structure of these materials from the chemical composition of the pitch precursor. This was related to the conditions of thermo-oxidation pre-treatment with inorganic acids, used to modify the composition of the initial pitch. In both cases carbon foams with uniform open cell structures were obtained, although they showed very different properties. When nitric acid was used in the initial thermo-oxidative treatment, the steam activation process of the carbon foam proceeded to a larger extent; the porosity parameters of this sample are twice higher than those obtained when using sulfuric acid. This was attributed to the catalytic effect of H2SO4 during the foaming step, which leads to the formation of dense carbon foams with highly ordered structure as inferred from XRD. At converse, densification of the carbon foam did not occur when using nitric acid in the initial thermo-oxidative treatment; the resulting material displayed labile surface groups decomposing at moderate temperatures, as well as an incipient microporosity, which further increased during the steam activation.