Preparation of grafted few-layer graphene from K-THF-graphite intercalation compounds by the addition of aldehyde

The preparation of graphene with large area, few layers, and without oxidation is required. Thus far, we have determined that by synthesizing graphite intercalation compounds (GICs) and adding water to them, it was possible to prepare few-layer graphene without oxidation; however, its area was small. Therefore, we investigated the addition of aldehyde (with different alkyl chain lengths containing electron-withdrawing groups, which allowed the use of an electrophilic addition reaction on carbon hexagonal layers) to GICs to prepare few-layer graphene with a large area and without oxidation. In this study, stage-1 ternary graphite intercalation compounds (K-THF-GICs) were synthesized using the solution method. Aldehyde solvents with different alkyl chain lengths were then added to K-THF-GICs, and the mixtures were stirred for 72 h. An attempt was made to prepare few-layer, small-area graphene with little oxidation. Results indicated that the addition of aldehyde containing an electron-withdrawing group to GICs promoted exfoliation with the electrophilic addition reaction on the carbon hexagonal layer, producing few-layer graphene. UV–vis (Ultraviolet・Visible Absorption Spectroscopy) results showed that solvents with long alkyl chains were more suitable for preparing few-layer graphene than solvents with short alkyl chains. According to Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, graphene exfoliated by decanal or octadecanal as three and two layers, respectively, was minimally oxidized and showed an area of several tens of μm2. Comparative analysis of the heat treatment of few-layer graphene demonstrated that it was possible to graft few-layer graphene exfoliated using decanal or octadecanal. Such grafting may be involved in exfoliation. Few-layer graphene was then prepared by adding an aldehyde solvent containing long alkyl chains to K-THF-GICs. Using octadecanal containing the longest alkyl chain among the solvents tested in this study, few-layer graphene with a thickness of 1.8 nm and an average area of 84 µm2 was obtained with little oxidation.