Dispersion behaviour of graphene oxide and reduced graphene oxide

doi:10.1016/j.jcis.2014.05.033

Journal of Colloid and Interface Science

Volume 430, 15 September 2014, Pages 108-112

https://doi.org/10.1016/j.jcis.2014.05.033 Get rights and content

Highlights

•
Investigation of GO and rGO dispersion behaviour in eighteen organic solvents.
•
Comparing the stability and the dispersion quality of the two derivatives.
•
Determining specific solubility values of GO and rGO.
•
Estimating the Hansen and Hildebrand parameters of GO and for the first time, of rGO.
•
Model for identifying mixtures of solvents for large-scale graphene ink production.

Abstract

The dispersion behaviour of graphene oxide (GO) and chemically reduced GO (rGO) has been investigated in a wide range of organic solvents. The effect of the reduction process on the GO solubility in eighteen different solvents was examined and analysed, taking into consideration the solvent polarity, the surface tension and the Hansen and Hildebrand solubility parameters. rGO concentrations up to ∼9 μg/mL in chlorinated solvents were achieved, demonstrating an efficient solubilization strategy, extending the scope for scalable liquid-phase processing of conductive rGO inks for the development of printed flexible electronics.

Graphical abstract

Introduction

Graphene is an atomically thin layer of sp²-bonded carbon atoms, stacked in a two-dimensional (2D) honeycomb lattice, forming the basic building block for carbon allotropes of any dimensionality [1]. Since its isolation as a monolayer, graphene has attracted an extraordinary amount of interest due to its potential application in the fastest growing scientific fields, such as supercapacitors [2], biosensors [3], photovoltaics [4] and touch panels [5].

Chemical vapour deposition (CVD) [6] and micromechanical exfoliation of graphite are the most widely used fabrication methods of less defective graphene films. However, the CVD deposition of uniform large area graphene films on arbitrary substrates at low temperatures is not possible and furthermore this method is incompatible with roll to roll mass production processes. At the same time, the exfoliated graphene exhibits very low solubility in common organic solvents [7], due to the essential addition of a stabilizer as the exfoliation liquid medium [8].

On the other hand, exfoliated graphene oxide (GO) is the ideal alternative for the production of solution processable graphene, as it can be synthesized in large quantities from inexpensive graphite powder and can readily yield stable dispersions in various solvents [9]. GO is an oxidized graphene sheet having its basal planes decorated mostly with epoxide and hydroxyl groups, in addition to carbonyl and carboxyl groups located at the edges [10].

The covalent character of C–O bonds disrupts the sp² conjugation of the hexagonal graphene lattice, making GO an insulator. Nevertheless, GO can be partially reduced to conductive graphene-like sheets by removing the oxygen-containing groups [11], [12], [13]. In this way the conjugated structure of graphene can be recovered, resulting in reduced graphene oxide (rGO) with important electrical properties partially restored [14].

However, the preparation of dispersed form of graphene for applications in printed flexible electronics is not a straightforward process, since its stability in various solvents is a critical point. In this context, the solubility of GO in various solvents has been recently examined by several groups [9], [15], [16]. However, there is a gap in the literature on the direct comparison on solubility values on GO and rGO, which in principle they are different. Therefore, the knowledge on how conductive rGO stable solution can be obtained in common organic solvents is vital.

In this work, the dispersion behaviour of GO and chemically rGO is compared, aiming to get an insight into how the removal of oxygen containing groups during the reduction process affects its dispersion quality. The solubility/dispersibility of rGO is investigated in eighteen different solvents and directly compared with the pristine GO. In this way, critical solubility values are recorded aiming at the application of conductive rGO inks on printed flexible electronic devices [17].

Section snippets

Results and discussion

For the preparation of GO and rGO dispersions, the products prepared as described in the Experimental Section (SI), were first grounded with a mortar and pestle. In order to compare the dispersion behaviour in the different solvents, the same quantity of GO and rGO powder (∼1 mg) was added to a given volume of solvent (∼2 mL), with an initial concentration of 0.5 mg/mL. GO and rGO dispersions were tested in the following organic solvents: (DI) water, acetone, methanol, ethanol, 2-propanol,

Conclusions

The dispersion behaviour of GO and rGO in eighteen solvents was compared. The Hansen and Hildebrand parameters of GO and rGO were estimated verifying that the reduction process has a strong effect on the solubility and stability. Solutions of GO in NMP, ethylene glycol and water presented significant long-term stability with solubility values reaching ∼8.7 μg/mL for NMP. While, the dispersion behaviour of GO changed after its reduction, presenting better interaction with solvents like o-DCB (∼9

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Short CommunicationDispersion behaviour of graphene oxide and reduced graphene oxide

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Results and discussion

Conclusions

Carbon

Carbon

Carbon

Nat. Mater.

Nano Lett.

Angew. Chem. Int. Ed.

Adv. Funct. Mater.

Nat. Nanotech.

Nano Lett.

Chem. Commun.

Langmuir

Langmuir

Short Communication
Dispersion behaviour of graphene oxide and reduced graphene oxide