Reducing Graphene Oxide to Graphene Using Environmentally Safe Materials

Graphene [1,2] has many potential electronic, optoelectronic and biological uses [3]. However, graphene itself is non-soluble and this makes it very difficult to deposit from solution (other than from non-stable suspensions). On the other hand, graphene oxide is highly soluble and very easy to deposit from inks and solutions [4], but is also insulating and so has very few electronic properties of interest.

Graphene StructureThe conversion of graphene oxide back to graphene is therefore of huge interest to both the scientific and industrial community. At the moment, this process is most typically done with extremely toxic and environmentally hazardous chemicals such as hydrazine and Lawesson's reagent.

The development of a technique to deposit graphene oxide onto a substrate in a uniform and even coating, and then convert it to graphene using only environmentally-safe chemicals would facilitate both R&D and industrial exploitation of the mechanical, optical and electrical properties of graphene.

Ossila produce a range of components and data sheets that can enable researchers to quickly and easily undertake this process, whilst making use of our existing infrastructure such as:

A thorough literature review suggested that using a naturally derived reducing agent, namely Vitamin C (L-ascorbic acid) [5,6], it is possible to reduce graphene oxide flakes deposited onto pre-fabricated test chips from an aqueous dispersion via spin coating. The results presented below are an adaption of the original work first reported by Zhang et al. in their 2010 paper [5].

The technique involves the submersion of the pre-fabricated test-chips in a solution of vitamin C in water at room temperature for several days. Optimization on the process time, temperature and concentration is currently ongoing, but initial results are highly promising and, in only a few days work, we were able to produce figures of merit close to those reported in the literature [5]. The rapid speed of progress is largely due to the use of the existing test chip infrastructure, which not only allows for fast electrical measurement but also for single-layer flakes of graphene (oxide) to be located under an optical microscope. This is due to the 300 nm thick silicon dioxide dielectric layer, which is crucial because this specific thickness provides suitable interference to enable the monolayer to be visible on the surface.

 

Interdigitated FET channels for measuring graphene
Figure 1: the active area of one of the 20 FET devices found on our high density substrates which have interdigitated source-drain electrons with 5 micron channel lengths.

 

Graphene flakes within Pt FET device channels
Figure 2: shows graphene oxide flakes across the platinum electrodes.

 

I-V and conductance data of a reduced graphene oxide FET deviceConductance of graphene oxide reduced over time
Figure 3: demonstration of the field-effect behaviour of graphene oxide devices which reduces over time. The device exhibits a conductance of 3.7 mS after 10 days reduction in vitamin C solution.

 

If you have any queries or would like more information on our graphene studies please do not hesitate to contact us.

 

References: (please note that Ossila has no formal connection to any of the authors or institutions in these references.)

[1] Nobel Lecture: Graphene: Materials in the Flatland. K.S. Novoselov, Rev. Mod. Phys., 83(3), 837–849 (2011)

[2] The rise of graphene. A.K. Geim & K.S. Novoselov, 6(3), 183–191 (2007)

[3] A roadmap for graphene. K.S. Novoselov et al., Nature, 490(7419), 192–200 (2012)

[4] Graphene oxide: preparation, functionalization, and electrochemical applications. D. Chen et al., Chem. Rev., 112(11), 6027–53 (2012)

[5] Reduction of graphene oxide via L-ascorbic acid. J. Zhang et al., Chem. Comm., 46(7), 1112–4 (2010)

[6] Chemical reduction of graphene oxide: a synthetic chemistry viewpoint. C.K. Chua & M. Pumera, Chem. Soc. Rev., 43(1), 291–312 (2014)

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