Fabrication of high-quality or highly porous graphene sheets from exfoliated graphene oxide via reactions in alkaline solutions

The applications of solution-exfoliated graphene oxide (GO) as an electrical/electrochemical conductor require rational design-based approaches. Herein, we show that reduced GO nanosheets with highly ordered or nanoporous structures can be fabricated by treatment of graphite oxide (GrO) having variable-oxidation-degree with hot KOH solution. As model systems, GrO powders fabricated by modified Brodie and Hummers methods (B-GrO and H-GrO, respectively) were exfoliated into GO in alkaline solutions (to afford B-KGO and H-KGO, respectively), followed by 2.5-h refluxing at 100 degrees C. Notably, B-KGO was exceptionally resistant to hot KOH solution, whereas H-KGO was partially reduced under these conditions, as confirmed by C-13 solid-state NMR, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy analyses. Moreover, reduced B-KGO featured highly ordered structures, whereas reduced H-KGO contained nanopores resulting from low-temperature activation in KOH solution. These extraordinary reactions of KGO nanosheets were translated into different electrical properties of reduced KGO nanosheets and different rheological properties of the corresponding pastes. (C) 2018 Elsevier Ltd. All rights reserved.