Azole-functionalized diacetylenes as precursors for nitrogen-doped graphitic carbon materials

Abstract

A novel strategy for the preparation of nitrogen-doped carbon is presented that is based on the use of azole-functionalized diacetylenic precursors (imidazole and benzimidazole). As demonstrated by thermal analyses (TGA, DSC) and spectroscopic measurements (IR, 13C solid-state NMR), these diacetylenic molecules undergo exothermic polyaromatization at low temperature. This process is independent of the intrinsic ability of the diacetylenes to undergo solid-state topochemical polymerization. At 800 °C, graphite-like structures incorporating nitrogen are obtained, as proven by XPS measurements. The nitrogen contents of the residues resulting from thermolysis at 800 °C are fairly high, 7.4 and 8.4 wt%, and these percentages amount to about 4 wt% at 1100 °C. This study also shows that mixing these diacetylenes with small amounts of FeCl2 prior to pyrolysis at 800 °C leads to porous carbon materials with relatively high surface areas, 253 and 281 m2 g−1. TEM photographs indicate that these porous carbon materials form graphitic nanostructures. Polydiacetylenes also decompose into graphite-like materials, and the degree of graphitization of these materials and their nitrogen contents are comparable to those of the residues obtained by pyrolysis of the diacetylene monomers. Thus, low molecular weight diacetylenic monomers are effective precursors to access graphite-like materials, and this process does not require the prior preparation of a polymer.