A Simple Melt Impregnation Method to Synthesize Ordered Mesoporous Carbon and Carbon Nanofiber Bundles with Graphitized Structure from Pitches

Abstract

In this paper, we report a simple melt impregnation method by using cheap mesophase pitches (MPs) as carbon precursors to prepare ordered mesoporous carbon with ordered graphitized pore walls at low temperature. This facile procedure includes melting MPs at 140 °C and impregnation of the melt into hexagonal or bicontinuous cubic mesoporous silica templates. After the removal of silica templates by HF solution, ordered mesoporous carbon materials with replica structures of 2-D hexagonal p 6 mm or cubic Ia 3̄ d symmetry were derived. The pore walls of the hexagonal mesoporous carbon products are composed of graphitized domains with the (002) crystallographic plane of the graphite perpendicular to the long axis of the carbon nanorods. Theoretical computations show that negatively charged O atoms of Si−OH and Si−O−Si from the surface of mesoporous silica channels can interact with the positive charged H atoms of the MPs, which makes the stacking units incorporate into the pores with the (002) plane vertical to the channels, and finally the oriented periodicity of the graphite domains is formed. N 2 sorption measurements show that the materials possess no micropores. For the bicontinuous cubic mesoporous carbon, HRTEM images show that the material is a true replica framework of Ia 3̄ d symmetry. The graphitized structure of the pore walls seems to have an orientation related to the bicontinuous pore structure, which could not be simply defined based on current TEM results. Graphitized carbon nanofiber bundles with a uniform diameter of about 7 nm were obtained by using Fe 2 O 3 nanoparticle doped mesoporous silica as a template. A spiral graphite structure was observed for the materials. Cyclic voltammetry measurements show low charge/discharge currents for the graphitized materials compared to the amorphous mesoporous carbon, further confirming the anisotropic character of the graphitized mesoporous carbons. The method can be widely applied to the hard-templating synthesis of graphitized carbon nanostructures and other doped carbon nanomaterials.