Surface chemistry of porous carbons from N-polymers and their blends with pitch

A series of activated carbons having from 0.8 to 7.2 wt.% of nitrogen substituted for carbon in graphene layer was prepared by steam activation of chars derived from polyacrylonitrile (PAN), oxidized form of polyvinylpyridine (PVPox) and their blends with coal-tar pitch (CTP). Porosity development at 50 wt.% burn-off was monitored using N2 adsorption at −196 °C and the surface chemistry was characterized by elemental analysis, X-ray photoelectron spectroscopy, pH of the point zero charge pHPZC and acid/base titration. Activated carbons from PAN and CTP/PAN blends show a similar moderate porosity development (SBET ∼ 800 m2 g−1). PVPox gives most microporous carbons (SBET ∼ 1400 m2 g−1) but the porosity diminishes with pitch contribution to blend. Substitutional nitrogen effectively enhances the basicity of the carbon surface. pHPZC increases proportionally to nitrogen content and reaches a maximum over 10 for PAN derived carbon of N/C ratio 0.07. Conversely, the maximum number of basic sites from titration with HCl, ∼2 mmol g−1, is found for PVPox carbon with a moderate nitrogen proportion (N/C = 0.025), however, with a superior porosity development. Introduction of nitrogen does not affect the number and distribution of acidic oxygen groups of activated carbon.