▎ 摘　　要

Graphene has received abundant attentions in many applications because of its extraordinary properties. Liquid-phase exfoliation is one of the most important methods to obtain graphene from graphite. However, due to strong van der Waals interaction force, it is still extremely challenging to further improve the exfoliation efficiency. Here we report that by carrying out reductions with the oxygenic functional groups on the pristine graphite edges using hydrazine hydrate and hydrogen at 800 degrees C as a pretreatment approach, the exfoliation efficiency can be improved by similar to 37% using a lithium-assisted liquid-phase exfoliation approach. The change of the functional groups is characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The graphene sheets show high degree of structural integrity and few defects. A thin film is prepared from the exfoliated graphene by vacuum assisted filtration and treated by annealing and mechanical compression. The graphene thin film shows a high thermal conductivity of 1707 Wm(-1) K-1, which is superior to that of common metal materials, such as Cu and Al. (C) 2018 Elsevier Ltd. All rights reserved.