Critical temperatures in the synthesis of graphene-like materials by thermal exfoliation-reduction of graphite oxide

We prepared a series of graphene-like materials by thermal exfoliation/reduction of a graphite oxide (GO) at temperatures between 127 degrees C and 2400 degrees C. The extent of the exfoliation and reduction of the GO at different temperatures, as well as the impact on the resultant graphene-like materials (TRGs), were studied through their chemical/structural characterization. The main oxygen loss was observed at 127 degrees C during the blasting of the GO, which produced its exfoliation into monolayer functionalized TRG with hydroxyl groups and minor amounts of epoxy and carboxyl groups. Above 600 degrees C, the reduction continued smoothly, with oxygen and hydrogen loss and the conversion of hybridised carbon atoms from sp(3) into sp(2). 1000 degrees C appears to be a critical temperature for the efficiency of the reduction process, as the resulting TRG contained <2% oxygen and 81.5% sp(2)-carbon atoms. The materials obtained at 2000 degrees C and 2400 degrees C were almost oxygen-free and the layers exhibited a dramatic restoration of the pristine graphite structure, as confirmed by the increase in the average size of the sp(2)-domains. The typical disordered stacking of TRGs increases with temperature, although they can be dispersed yielding monolayers at 127 and 300 degrees C and stacks of up to 4-6 layers above 1000 degrees C, as determined by AFM. (c) 2012 Elsevier Ltd. All rights reserved.