▎ 摘　　要

Since 2004 and the awarding of the Nobel Prize for the discovery of graphene there has ensued a worldwide research effort to study and capitalize on the unique properties of graphene. A great deal of that research utilizes graphite as a starting material and strongly oxidizes it to produce graphene oxide. In this review an alternate way to produce graphene oxide that utilizes a less expensive carbon source and that requires less dangerous and environmentally impactful chemicals is reviewed. The carbon source is leonardite, which is a low grade lignite coal that occurs in many lignite deposits. Humic add (HA) is the base extractable organic matter commonly found in soil. HA, extracted from leonardite, is highly oxidized and contains a number of oxygenated groups around the edges of the graphene like core. This material is very similar to graphene oxide (GO) produced by add oxidation of graphite. This HA extract has been utilized as a starting material rather than graphite for producing GO and ultimately graphene. This paper reviews the characterization of this material as compared to GO, reduction and functionalization of the extract by several different chemical and thermal means, and reduction of the HA to graphene, and several applications of the reduced HA. This approach potentially provides a low cost source for reduced functionalized graphene nanosheets for large scale production. (C) 2015 Elsevier Ltd. All rights reserved.