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An Iron-Based Green Approach to 1-h Production of Single-Layer Graphene Oxide

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An Iron-Based Green Approach to 1-h Production of Single-Layer Graphene Oxide

Li Peng et al. Nat Commun.

Abstract

As a reliable and scalable precursor of graphene, graphene oxide (GO) is of great importance. However, the environmentally hazardous heavy metals and poisonous gases, explosion risk and long reaction times involved in the current synthesis methods of GO increase the production costs and hinder its real applications. Here we report an iron-based green strategy for the production of single-layer GO in 1 h. Using the strong oxidant K2FeO4, our approach not only avoids the introduction of polluting heavy metals and toxic gases in preparation and products but also enables the recycling of sulphuric acid, eliminating pollution. Our dried GO powder is highly soluble in water, in which it forms liquid crystals capable of being processed into macroscopic graphene fibres, films and aerogels. This green, safe, highly efficient and ultralow-cost approach paves the way to large-scale commercial applications of graphene.

Figures

Figure 1
Figure 1. Large-scale synthesis of single-layer GOFe via K2FeO4-based methodology.
(a) Seventy-five litre GOFe aqueous solution with a concentration of 10 mg ml−1. (b) GOFe solution in H2O and N,N-dimethylformamide (DMF) with a concentration of 3 mg ml−1. (c) SEM image of GOFe on Si/SiO2 substrate. (d) The size distribution of the GOFe sheets, counted and calculated from c and Supplementary Fig. 2. (e) TEM image of GOFe and its SAED diffraction patterns (inset). (f) Tapping mode AFM image and height profile of GOFe. (g) GOFe solution of H2O and DMF with a concentration of 3 mg ml−1 after storage for 1 year. (h) Image of aqueous LCs in a quartz tube between crossed polarisers and POM image between crossed polarisers in planar cells of aqueous GOFe LCs at a concentration of 3 mg ml−1. Scale bars, 20 μm (c), 2 μm (e), 4 μm (f) and 5 mm (h, left), 1 μm (h, right).
Figure 2
Figure 2. Comparison of GOFe and GOMn.
(a) Raman spectra recorded using 514 nm laser excitation, (b) XRD spectra, (c) ultraviolet–visible spectra recorded in aqueous solution at 0.05 mg ml−1, (d) TGA plots, (e) Fourier transform infrared spectra and (fh) XPS spectra and its C1s XPS spectra of GOFe and GOMn. 1 and 2 denote GOFe and GOMn, respectively. All of these data show that GOFe and GOMn have similar composition and structures.
Figure 3
Figure 3. Mechanism of GOFe synthesis with the oxidant of K2FeO4.
The whole synthetic process (1 h) contains two main stages: intercalation–oxidation (IO) and oxidation–exfoliation (OE). The in situ generated FeO42− and atomic oxygen [O] act as oxidants and the O2 formed from residual [O] provides mild and durative gas exfoliation. In the IO stage, the concentrated sulphuric acid and oxidants intercalate into the layers of graphite to form intercalated graphite oxide (GIO). During the intercalation, the oxidants break the π–π conjugated structures of graphite, generating negatively charged functional groups, and increasing the interlayer spacing. In the following OE stage, the oxidants further oxidize the carbon basal planes of GIO, giving rise to more functional groups and enlarging the interlayer space. After recycling of sulphuric acid and washing with water, 100% slGO is achieved.
Figure 4
Figure 4. Kinetics of the synthesis of GOFe.
(a) XRD spectra of the samples taken from the synthesis process at the reaction times=0 min, 3 min, 5 min, 8 min, 11 min, 15 min 30 min, 45 min, 1 h and 2 h (110), respectively. (b) Interlayer spacing of selected samples at the OE stage versus reaction time. (c) TGA plots of the same samples as shown in a. (d) Weight loss of GOFe at 600 °C (left, red) and corresponding zeta potential (right, blue) as a function of reaction time. The kinetics of GOFe confirms that the whole reaction process completes in 1 h, including ~15 min of intercalation–oxidation and 45 min of oxidization–exfoliation. (e) Sample-H, Sample-T and GOFe (2 mg ml−1) placed in water, indicating that only GOFe is well-soluble. (f) XRD spectra, (g) C1s XPS spectra and (h) TGA plots of GOFe, Sample-H and Sample-T with the reaction time 1 h. (ik) SEM images of graphite, Sample-T and Sample-H, showing that the conventional Hummers methods with the oxidant of KMnO4 can only result in thick graphite-like particles rather than slGO in 1 h of reaction time. Scale bar, 20 μm (ik).
Figure 5
Figure 5. Spray-dried GOFe powder for re-dissolving.
(a) Fresh GOFe LC solution of H2O with a concentration of 6 mg ml−1. (b) Macroscopic photograph of spray-dried GOFe powders with a density of 224 mg cm−3. (c,d) SEM images of GOFe powders, showing that the GOFe individual particles have a peony-like morphology. The insert of d is a peony. (e) Re-dissolved GOFe solutions of H2O and N,N-dimethylformamide with a concentration of 4 mg ml−1. (f) SEM image of re-dissolved single-layered GOFe sheets on Si/SiO2 substrate. (g) Tapping mode AFM image and height profile of re-dissolved GOFe. (h) POM images of re-dissolved GOFe aqueous LCs in a quartz tube and a planar cell between crossed polarisers at a concentration of 4 mg ml−1. Scale bars, 3 μm (c), 500 nm (d), 10 μm (f), 2 μm (g) and 5 mm (h, left), 1 μm (h, right).
Figure 6
Figure 6. Macroscopic assembled materials of re-dissolved GOFe.
(ac) A wet-spun 14-m long continuous fibre with diameter 10 μm and its SEM images at the cross-section of fibre. (df) A film made by the filtration method and its SEM image of a section. (gi) Ultralight weight GOFe aerogel with a density of 2 mg cm−3 and its SEM images showing CNT-coated graphene morphology. Scale bars, 3 cm (a), 1 μm (b), 500 nm (c), 1 cm (d), 3 μm (e), 400 nm (f), 2 cm (g), 30 μm (h) and 2 μm (i).

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