▎ 摘　　要

Graphene is an appealing two-dimensional material with superior mechanical, electrical, and thermal properties. Mass production of high-quality graphene is attracting more and more researchers' attention in recent years. Most of the current methods for synthesizing graphene use purified chemical reagents that could be expensive for large-scale production. In this study, we have developed a less expensive method to synthesise high-quality graphene sheets from wheat straw via a combined hydrothermal and graphitization approach. The resulting graphene sheets show favorable features such as ultrathin nanosheet frameworks (2-10 atomic layers), high graphitization (up to 90.7%), graphite-like interlayer spacing (0.3362 nm), and the mesoporous structure. When used as an anode material for lithium ion batteries, the few-layer graphene delivers high reversible capacity (502 mAh g(-1) at 0.1 C), superior rate capability (463.5, 431.4, and 306.8 mAh g(-1) at 1, 2, and 5 C, respectively), and good cycling performance (392.8 mAh g(-1) at 1 C after 300 cycles). The wheat straw-derived graphene sheets also display the relatively flat voltage profiles with a negligible charge/discharge voltage hysteresis. Moreover, this low-cost, highly efficient, and catalyst-free technique is a significant milepost towards environmentally-sustainable, commercially feasible fabrication of carbon nanomaterials from renewable natural resources. (C) 2016 Elsevier B.V. All rights reserved.