Please cite this article in press as: V.B. Mohan, et al., Mater. Sci. Eng. B (2014), http://dx.doi.org/10.1016/j.mseb.2014.11.002 ARTICLE IN PRESS G Model MSB 13644 1–12 Materials Science and Engineering B xxx (2014) xxx–xxx Contents lists available at ScienceDirect Materials Science and Engineering B jo ur nal ho me page: www.elsevier.com/locate/mseb Characterisation of reduced graphene oxide: Effects of reduction variables on electrical conductivity Velram Balaji Mohan ∗ , Reuben Brown, Krishnan Jayaraman, Debes Bhattacharyya Q1 Centre for Advanced Composite Materials (CACM), Department of Mechanical Engineering, Building 740-181, Tamaki Campus, 261 Morrin Road, Glen Innes The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand a r t i c l e i n f o Article history: Received 20 June 2014 Received in revised form 22 September 2014 Accepted 5 November 2014 Available online xxx Keywords: Graphene oxide Reduced graphene oxide Q3 Reduction Raman spectroscopy X-ray diffraction X-ray photoelectron spectroscopy d-Spacing Electrical conductivity a b s t r a c t Graphene is a useful material Q2 because of its excellent electronic and physical properties. Graphene and its derivatives can be used as functional reinforcements in polymers for applications, such as sensors, flexible devices, packaging, and functional nanocomposites. This article focuses on the synthesis, reduction using three different reductants (hydrobromic acid, hydrazine hydrate and hydroiodic acid) and characteri- sation (using Raman spectroscopy X-ray diffraction and X-ray photoelectron spectroscopy) of reduced graphene oxide in order to systematically maximise its electrical conductivity and identify a structure with physical properties which possesses higher electrical conductivity. Results for reduced graphene oxide film that has been reduced with hydroiodic acid show an electrical conductivity of 103.3 S cm -1 with better flexibility compared to rGOs reduced by hydrobromic acid and hydrazine hydrate. © 2014 Published by Elsevier B.V. 1. Introduction Mechanically superior, with thickness in the micro/nano-metre range [1], self-supporting graphene oxide (GO) films can have a wide range of applications in electronic (a flexible electrode made out of graphene is shown in Fig. 1) and biomedical devices [2–10]. Deemed the thinnest material in existence, graphene can be con- sidered as a building block for all other carbon nano-fillers [11–13]. Such materials exhibit potential for applications in the areas of aerospace, construction, automotive, fluid separation and elec- tronics [14,15]. Reduced graphene oxide (rGO) exhibits properties between those of graphene and GO, with the reduction process influencing these properties strongly. Many different reduction methodologies have been used [14,17–31] in an attempt to increase the efficiency of the reduc- tion process and improve the final properties of the rGO. However the widely varying results obtained by these methods mean that their effects on the structure of graphene oxide are still under ∗ Corresponding author. Tel.: +64 2108168842. E-mail addresses: vmoh005@aucklanduni.ac.nz (V.B. Mohan), reuben.brown@auckland.ac.nz (R. Brown), k.jayaraman@auckland.ac.nz (K. Jayaraman), d.bhattacharyya@auckland.ac.nz (D. Bhattacharyya). discussion. Furthermore, there is not much work done in the cre- ation of useful combined rGO based composites [32] and even less work on systematic measurements of mechanical, electrical and chemical properties [13,28,33,34] of these systems. This study takes a systematic synthesis approach to add com- parative detail to the discussion on the reduction efficiency of GO using hydrohalic acids and the effects of these synthetic methods on the properties of interest, especially the electrical conductivity of the reduced graphene oxide (rGO) films. Electrical conductiv- ity is important in the applications of nano-electronics, such as super-capacitors, transparent conductors, sensors, storage cells, and actuators [4,17,35–39]. In addition, it has been demonstrated that chemically modified graphene and its derivatives can be rein- forced in a polymeric or inorganic matrix with better dispersion to make electrically conducting composites that have many potential practical applications [11,32,35,40–50]. Raman spectroscopy is a commonly used method to charac- terise carbon products as conjugated and double carbon–carbon bonds lead to high Raman intensities [51]. XRD is used to analyse structural changes [52], especially d-spacing variations in rGO lay- ers at different reduction conditions. Scanning electron microscopy (SEM) has been used to characterise the changes in microstructure of rGO [48,53–56]. Characterisation of rGOs by Raman spec- troscopy and X-ray diffraction demonstrate the chemical reduction http://dx.doi.org/10.1016/j.mseb.2014.11.002 0921-5107/© 2014 Published by Elsevier B.V. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66