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

• Published in: Microporous and mesoporous materials 2005-07, Vol.82 (1), p.113-120
• Main Authors: Machnikowski, J., Grzyb, B., Machnikowska, H., Weber, J.V.
• Format: Article
• Language: English
• Subjects: Acid/base properties; Activated carbon; Adsorbents; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; N-polymers; Nitrogen substitution; Porous materials; Pyrolysis; Surface physical chemistry
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2005.03.004

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 N 2 adsorption at −196 °C and the surface chemistry was characterized by elemental analysis, X-ray photoelectron spectroscopy, pH of the point zero charge pH PZC and acid/base titration. Activated carbons from PAN and CTP/PAN blends show a similar moderate porosity development ( S BET ∼ 800 m 2 g −1). PVPox gives most microporous carbons ( S BET ∼ 1400 m 2 g −1) but the porosity diminishes with pitch contribution to blend. Substitutional nitrogen effectively enhances the basicity of the carbon surface. pH PZC 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.