▎ 摘　　要

In this work, graphene is facilely prepared by direct exfoliation of graphite in aqueous media with the assistance of alkali lignin (AL). The graphite is successfully exfoliated into single- and multi-layer graphene, with about 20% monolayer ones, and the concentration of graphene in the aqueous dispersions can reach 0.65 +/- 0.03 mg mL(-1). The nanosheets are stabilized in the dispersions owing to pi-pi interaction between the graphene and AL, and the electrostatic repulsion between negative charged AL, as verified by fluorescence and zeta-potential measurements. The results also show that there are very few defects in the basil-plane of the graphene so that the free-standing graphene films prepared from the dispersions exhibit good electrical conductivity. Finally, the addition of only 0.1 wt% such graphene sheets to an epoxy resin gives 15%, 49%, and 97% enhancement in tensile strength, critical stress intensity factor and critical strain energy release rate, respectively. (C) 2014 Elsevier Ltd. All rights reserved.