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Controllable Edge Oxidation and Bubbling Exfoliation Enable the Fabrication of High Quality Water Dispersible Graphene

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ABSTRACT

Despite significant progresses made on mass production of chemically exfoliated graphene, the quality, cost and environmental friendliness remain major challenges for its market penetration. Here, we present a fast and green exfoliation strategy for large scale production of high quality water dispersible few layer graphene through a controllable edge oxidation and localized gas bubbling process. Mild edge oxidation guarantees that the pristine sp2 lattice is largely intact and the edges are functionalized with hydrophilic groups, giving rise to high conductivity and good water dispersibility at the same time. The aqueous concentration can be as high as 5.0 mg mL−1, which is an order of magnitude higher than previously reports. The water soluble graphene can be directly spray-coated on various substrates, and the back-gated field effect transistor give hole and electron mobility of ~496 and ~676 cm2 V−1 s−1, respectively. These results achieved are expected to expedite various applications of graphene.

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Bubbling exfoliation of edge oxidized graphite for water soluble graphene.(a) Schematic diagram of preparation process. Left: oxidation at graphite edges; middle: bubbling and exfoliation; right: dispersion. (b) Raman ID/IG mapping image on a 50 μm × 50 μm graphite, showing most defects located around the edges. (c) SEM image of an edge oxidized graphite. (d) Digital photographs of bubbling process of 0.5 g precursor in 80 mL bubbling reagent for 0, 5 and 15 min, respectively. (e) Digital photographs of 20 L, 2.5 mg mL−1 graphene aqueous solution prepared through the bubbling exfoliation. Scale bar, 10 μm (c).
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f1: Bubbling exfoliation of edge oxidized graphite for water soluble graphene.(a) Schematic diagram of preparation process. Left: oxidation at graphite edges; middle: bubbling and exfoliation; right: dispersion. (b) Raman ID/IG mapping image on a 50 μm × 50 μm graphite, showing most defects located around the edges. (c) SEM image of an edge oxidized graphite. (d) Digital photographs of bubbling process of 0.5 g precursor in 80 mL bubbling reagent for 0, 5 and 15 min, respectively. (e) Digital photographs of 20 L, 2.5 mg mL−1 graphene aqueous solution prepared through the bubbling exfoliation. Scale bar, 10 μm (c).

Mentions: Our approach is clearly illustrated in the schematic diagram of Fig. 1a and the bubbling process of Supplementary Video 1. At first, the controllable weak oxidization in the mixture of sulfuric acid and potassium permanganate (KMnO4) facilitates the wetting of graphite in water and the edge opening of layered graphite sheets, while keeping most basal planes of graphite intact; Then, the exfoliation is accomplished by interlayer gas bubbling process of the precursor in the mixture of hydrogen peroxide (H2O2) and ammonia (NH3). The weak oxidation on the graphite edges was realized through controlling mass ratios between oxidant KMnO4 and natural graphite. The typical mass ratio of KMnO4 and natural graphite is 1:1, and the reaction temperature and time is 25 °C and 2 h, respectively. Compared with generally reported Hummers or modified Hummers, as shown in Supplementary Table 1, we employed less oxidant, low temperature and very short reaction time, which results in lower oxygen content and higher C/O ratio of 5.34, as shown in the X-ray photoelectron spectroscopy (XPS) of oxidized graphite data in Supplementary Fig. S1. The oxygen content from XPS is 15.7 at.%, which is double confirmed by CHN elemental analysis. We propose that oxygen mainly locates on the edges and the surface of graphite sheets. The total atomic layer number is more than 2.5 × 104 for a graphite flake with 10 μm thickness, and the surface atomic layers will protect the inner layers from further oxidation while the edges have more defects as “weak” points to be attacked, and the space between graphite layers provides possibility for intercalation from the edges.


Controllable Edge Oxidation and Bubbling Exfoliation Enable the Fabrication of High Quality Water Dispersible Graphene
Bubbling exfoliation of edge oxidized graphite for water soluble graphene.(a) Schematic diagram of preparation process. Left: oxidation at graphite edges; middle: bubbling and exfoliation; right: dispersion. (b) Raman ID/IG mapping image on a 50 μm × 50 μm graphite, showing most defects located around the edges. (c) SEM image of an edge oxidized graphite. (d) Digital photographs of bubbling process of 0.5 g precursor in 80 mL bubbling reagent for 0, 5 and 15 min, respectively. (e) Digital photographs of 20 L, 2.5 mg mL−1 graphene aqueous solution prepared through the bubbling exfoliation. Scale bar, 10 μm (c).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5036305&req=5

f1: Bubbling exfoliation of edge oxidized graphite for water soluble graphene.(a) Schematic diagram of preparation process. Left: oxidation at graphite edges; middle: bubbling and exfoliation; right: dispersion. (b) Raman ID/IG mapping image on a 50 μm × 50 μm graphite, showing most defects located around the edges. (c) SEM image of an edge oxidized graphite. (d) Digital photographs of bubbling process of 0.5 g precursor in 80 mL bubbling reagent for 0, 5 and 15 min, respectively. (e) Digital photographs of 20 L, 2.5 mg mL−1 graphene aqueous solution prepared through the bubbling exfoliation. Scale bar, 10 μm (c).
Mentions: Our approach is clearly illustrated in the schematic diagram of Fig. 1a and the bubbling process of Supplementary Video 1. At first, the controllable weak oxidization in the mixture of sulfuric acid and potassium permanganate (KMnO4) facilitates the wetting of graphite in water and the edge opening of layered graphite sheets, while keeping most basal planes of graphite intact; Then, the exfoliation is accomplished by interlayer gas bubbling process of the precursor in the mixture of hydrogen peroxide (H2O2) and ammonia (NH3). The weak oxidation on the graphite edges was realized through controlling mass ratios between oxidant KMnO4 and natural graphite. The typical mass ratio of KMnO4 and natural graphite is 1:1, and the reaction temperature and time is 25 °C and 2 h, respectively. Compared with generally reported Hummers or modified Hummers, as shown in Supplementary Table 1, we employed less oxidant, low temperature and very short reaction time, which results in lower oxygen content and higher C/O ratio of 5.34, as shown in the X-ray photoelectron spectroscopy (XPS) of oxidized graphite data in Supplementary Fig. S1. The oxygen content from XPS is 15.7 at.%, which is double confirmed by CHN elemental analysis. We propose that oxygen mainly locates on the edges and the surface of graphite sheets. The total atomic layer number is more than 2.5 × 104 for a graphite flake with 10 μm thickness, and the surface atomic layers will protect the inner layers from further oxidation while the edges have more defects as “weak” points to be attacked, and the space between graphite layers provides possibility for intercalation from the edges.

View Article: PubMed Central - PubMed

ABSTRACT

Despite significant progresses made on mass production of chemically exfoliated graphene, the quality, cost and environmental friendliness remain major challenges for its market penetration. Here, we present a fast and green exfoliation strategy for large scale production of high quality water dispersible few layer graphene through a controllable edge oxidation and localized gas bubbling process. Mild edge oxidation guarantees that the pristine sp2 lattice is largely intact and the edges are functionalized with hydrophilic groups, giving rise to high conductivity and good water dispersibility at the same time. The aqueous concentration can be as high as 5.0 mg mL−1, which is an order of magnitude higher than previously reports. The water soluble graphene can be directly spray-coated on various substrates, and the back-gated field effect transistor give hole and electron mobility of ~496 and ~676 cm2 V−1 s−1, respectively. These results achieved are expected to expedite various applications of graphene.

No MeSH data available.


Related in: MedlinePlus