Facile preparation of reduced graphene by optimizing oxidation condition and further reducing the exfoliated products
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A cost-effective and highly efficient method was proposed for preparing reduced graphene (rEG) by modified Hummers approach. The influence of ratio of KMnO4 to graphite, oxidation time and oxidation temperature on oxidative degree of graphite oxide (GO) was investigated by x-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The thermal exfoliated graphene (EG) was characterized with transmission electron microscopy (TEM), FTIR, Raman spectrum and Brunauer–Emmett–Teller (BET) method. The EG was treated for 4 h at 800 °C with H2/Ar mixed atmosphere (15/85, v%) to remove the residual functional groups. The characterization of x-ray photoelectron spectroscopy (XPS) showed that rEG contains less functional groups than EG, which shows the C/O ratio increased from 10.6 (EG) to 34.71 (rEG). The results indicate that treating EG with a mixed H2/Ar atmosphere (15/85, v%) remarkably removes residual functional groups of EG, supplying a simple and feasible approach with large scale production of reduced graphene.
I. INTRODUCTION 2
Graphene, one-atom-thick layer of sp -hybridized carbon atoms arranged in a hexagonal lattice, has gained extensive attention due to its impressive electronic, optical, magnetic, thermal, and mechanical properties.1–3 It is used in several important areas such as supercapacitors, gas storage media, sensors, and lithium ion batteries.4–6 Many methods have been used to prepare graphene sheets, which includes micromechanical cleavage of highly ordered pyrolytic graphite (HOPG), 7 chemical vapor deposition (CVD), 8 liquid-phase exfoliation of expanded graphite and graphite,9,10 arc-discharge,11,12 transforming from carbon nanotubes13 and the chemical oxidation–reduction of exfoliated graphite oxide.14–16 Although these methods have been successful in producing graphene, time-consuming processes led to high production costs, therefore, how to effectively massproduce graphene-based materials is still arousing the interest of researchers. The chemical oxidation-reduction method is widely considered as a promising approach for large-scale prepare graphene sheets (GSs), it includes the Brodie,17 Hummers,18 and Staudenmaier methods.19 In these methods parent graphite is oxidized to graphite oxide (GO). On the one hand, the structure and chemical properties of GOs vary in the different oxidative degree: Contributing Editor: Mauricio Terrones a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.476
the formation of hydroxyl and carboxyl groups was detected at a lower oxidation level while epoxide groups formed at a higher level, we studied the order disruption in AB stacking during the increase in high oxidative levels have been studied.20 The use of strong acids and oxidants severely damages the sp2-bonded of graphene and deteriorates its performance in various applications even though these damages could be recovered partly by subsequent reduction process.21 By tuning the sp2/sp3 ratios of the carbon atoms the structure of GOs can be altered
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