Adsorption and structural properties of mesoporous carbons obtained from mesophase pitch and phenol-formaldehyde carbon precursors using porous templates prepared from colloidal silica

Abstract

Synthesis of carbons with uniform spherical mesopores is explored from mesophase pitch and polymerized phenol-formaldehyde carbon precursors using porous templates prepared from silica colloids having diameters of 16, 31 and 46 nm. It is shown that the polymer-based carbons exhibited very large pore volumes (between 3.5 and 4.0 cc g⁻¹) and complex pore size distributions because of incomplete filling of silica templates. In contrast, mesophase pitch filled all pores of the silica templates, which led to the carbons with uniform spherical mesopores reflecting the size of the silica colloids used. There is some evidence for mesostructural ordering in the pitch-based carbons obtained by using silica templates assembled from uniform colloids of diameters greater than 30 nm. This ordering is clearly visible for the pitch-based carbon obtained by using the silica template consisting of 46 nm colloids, which demonstrates the feasibility of colloidal crystal synthesis from uniform spheres of size below 50 nm. These unique structural properties of pitch-based carbons are reflected by paralleled capillary condensation and steep evaporation steps of nitrogen adsorption isotherm, which indicates high uniformity of mesopores and mesopore windows.