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, 13 C 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 FeCl 2 prior to pyrolysis at 800 C leads to porous carbon materials with relatively high surface areas, 253 and 281 m 2 g À1 . 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.

Diacetylenes with Ionic‐Liquid‐Like Substituents: Associating a Polymerizing Cation with a Polymerizing Anion in a Single Precursor for the Synthesis of N‐Doped Carbon Materials

“…Remarkably,t hese nitrogen contents are very close to those attained previously with neutral precursors. [11] This is consistent with the formation, at some stage of the decomposition path of 1·Br and 2·Br,o fn eutrals peciesa nalogous to those produced by thermolysis of 1 and 2 (see above).…”

“…Thise vent corresponds to the formation of ap olymer by cross-linking of the diacetylenic units. [11] Various polymeric structures have been described depending on the type of precursor used. In the case of at opochemically reactived iacetylene, 1,4-addition occurs to produce a p-conjugated polymerw ith an enyne structure.…”

“…This simple procedure does not requiret he prior preparation of ap olymer. [11] Owing to their high reactivity,t hese low-molecularweighta nd soluble precursors undergo polycyclization in the early stages of the heat treatment to yield graphite-likes tructures, and thus any vaporizationi sp revented and the loss of volatile fragments limited.T or eachh igher Nc ontentsw hile keeping the advantage of soluble precursors that can be depositedo nv arious substrates by impregnation or spraying before heat treatment, we turned to an alternative strategy inspired by ILs. Indeed, quaternizationo ft he previously described neutral precursors followed by anion metathesis opens the way to al arge variety of imidazolium and benzimidazolium precursors.…”

“…Such results underpin the pivotalrole of the diacetylene fragment in the precursor for the preparation of carbon materials, as already noted in ap revious study on neutral diacetylenes. [11] X-ray powder diffraction, Raman spectroscopy,a nd X-ray photoelectron spectroscopy (XPS) showed that the pyrolysates all have graphite-like structures, and adsorption measurements with krypton at 77 Ks howed that these solids are nonporous.A se xpected, the highest nitrogen contents were found for the precursors bearing nitrogen-rich anions, but reasonable values were also observedwith the bromide salts. The results obtained with the latter salts are in keeping with those reported recently for bisulfate-containing precursors.…”

One-step, template-free synthesis of highly porous nitrogen/sulfur-codoped carbons from a single protic salt and their application to CO2 capture

“…32 The cumulative surface area as a function of the pore size was further analyzed using the NLDFT method (slit/cylinder pores). 46,[60][61][62] The G mode had E2g symmetry that involved the in-plane bond-stretching motions of pairs of sp 2 -hybridized C atoms, and this mode does not require the presence of a sixmembered ring. More specifically, the cumulative surface areas for both AN-8 and AN-10 were saturated at 3.5 nm, while AN-7 attained the highest value at 2.2 nm.…”