Partial graphitization of activated carbon by surface acidification

Abstract

The microstructure of three activated carbons showed direct dependence with the concentration of particular surface oxygen groups (SOGs), as implemented by dilute, sequential nitric acid treatments (10% v/v). Previous work concerning one of the three carbons displayed a SOG/π-bond structure relationship. Herein, this relationship is expanded by examining the impact of SOG implementation on crystallite structure. Progressive oxidation revealed proportional changes in microstructure for activated carbons that originally contained a low density of total acidity (DTA). Increasing total surface acidity was associated with fewer but elongated single graphene layers (↑R-value, ↑La), increased stacking height (↑Lc) due to assembly of the elongated single graphene layers, and increased graphite-like order (↓Raman I(D):I(G) ratios). The re-mobilization of π-bond density and proportional enhancement of crystallite dimensions failed when DTA was excessive on the carbon surface, with additional SOG concentration promoting graphite-like disorder. The dominant SOG proposed to be responsible for structure change was carboxylic acids for granulated carbons and pyrones for more amorphous powered carbon as supported by corroborating DRIFTs and Raman trends. Dominant SOGs were determined to conjugate the surface and basal plane bulk, as attaching SOGs transform aromatic π-density into olefin-type bonding, enabling the respective crystallite changes.