The influence of three different intercalation techniques on the microstructure of exfoliated graphite

Abstract

The characteristics of exfoliated graphite derived from three intercalation methods: gas phase intercalation of iron (III) chloride, modified Hummers method and an electrochemical technique, were compared. Despite the absence of strong oxidisers the electrochemical method produced a material which is very similar to that of the modified Hummers method in virtually every respect. These both produced a graphite oxide based material whilst the gas phase method resulted in a stage 1 intercalation compound. The different materials demonstrated very distinctive exfoliation behaviour. The gas phase material exhibits 3% mass loss during expansion but has a large amount of residual intercalant. The graphite oxide based methods result in mass loss of up to 25% in the expansion zone. For all three samples the residual impurities lead to a reduction in oxidative resistance. Once removed all samples exhibit nearly identical oxidation behaviour. All three methods delivered graphite nanoplatelets with a very high aspect ratio through considerable expansion. Surprisingly the gas phase method caused persistent residual damage. All three methods yielded a product with varying levels of basal and edge damage, but the purified Hummers material exhibited marginally more ‘ideal’ characteristics. The simplest but still effective technique was found to be the electrochemical approach.