Materials Science and Engineering B 167 (2010) 133–136 Contents lists available at ScienceDirect Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb A novel synthesis of graphene by dichromate oxidation Sourov Chandra, Sumanta Sahu, Panchanan Pramanik ∗ Nanomaterials Laboratory, Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India article info Article history: Received 3 July 2009 Received in revised form 12 October 2009 Accepted 17 January 2010 Keywords: Graphene sheets Graphene oxide Nano ribbon Zeta potential abstract A novel synthetic route has been developed to produce very stable aqueous dispersed graphene sheets from the pristine graphite by oxidation with dichromate followed by reduction with hydrazine. The particle size, physical feature and zeta potential of graphene oxide show better than that of the modified Hummer’s method. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Graphene and graphene-based nano composites nowadays have much importance due to their exceptional electronic [1] and mechanical properties [2]. For those properties graphene-based nano composites are unique materials for microelectrical devices [3], sensors [4], biomedicines [5], mechanic resonators [6], ultra- capacitors [7] etc. Graphene has been synthesized by various methods including scotch tape method [8], electrostatic deposition of graphene [9], thermal or chemical decomposition of graphitic materials [10], thermal [11], chemical [12] and mechanical [8] exfo- liation, chemical vapour deposition [13] etc. In case of chemical exfoliation, at first graphite is converted to its oxide (GO) or epox- ide by modified Hummer’s method [14,15] using KMnO 4 or using potassium chlorate [16] or m-CPBA [17] (in case of epoxide) as an oxidant. Chemical vapour deposition (CVD) method is the best pro- cess for the synthesis of graphene for microelectronic industry, and the material produced by solution route is not comparable with the material produced by CVD for this class of application. The graphene generated by solution-oxidation (chemical exfoliation) finds some other areas of applications like sensor, catalyst-support, compos- ite, drug delivery, and gas storage. The graphene sheets produced by chemical oxidation have been used as the electrodes for ultra- capacitors or sensors due to their high surface area, as reported by Ruoff and co-workers [7]. Graphene oxide is highly dispersible in water and it could be easily deposited onto SiO 2 substrates by spin coating. After reduction it shows reasonable electrical con- ∗ Corresponding author. Tel.: +91 9434016995; fax: +91 3222 255303. E-mail addresses: panchanan 123@yahoo.com, pramanik1946@gmail.com (P. Pramanik). ductivity and hence it generates graphene-based semiconductors [3,18]. All the available methods have many serious inconveniences. When KMnO 4 is used, the removal of MnO 2 generated from the reaction involves a tedious process using H 2 O 2 . Again when KClO 3 is used, it generates a lot of chlorine dioxide gas and the mix- ture is highly hazardous. Similar situation is with m-CPBA as an oxidant. To overcome all these inconveniences, the process that involves a simple oxidation by acidified dichromate has been devel- oped through this investigation. It does not involve the removal of any precipitated product from the reaction mixture. The precip- itate of exfoliated graphite oxide is sonicated to form separated graphene oxide sheet and finally graphene sheet is formed by conventional reduction with hydrazine. The quality of chemically produced graphene-oxide and graphene by this process is similar to that of the reported one. So it may find applications in place of GO and graphene (by Hummer’s method) in various fields. 2. Experimental procedure In this procedure, at first graphite oxide was prepared from expandable graphite using K 2 Cr 2 O 7 as an efficient oxidant. Briefly, 5 g of graphite and 3.75 g of NaNO 3 were mixed in a conical flask. Then the mixture was kept in an ice bath and 375 ml of conc. H 2 SO 4 was poured into it with constant stirring. Subsequently 37.6 g of K 2 Cr 2 O 7 was slowly added over about 2 h with constant stirring. Stirring was again continued for 2 h in ice bath. After that mixture was continuously stirred for 5 days at room temperature. The initial colour of the solution became dark yellow, which turned to dark green after 4 days. After 5 days of stirring 750 ml of 5% aqueous H 2 SO 4 was slowly added to the above mixture over about 1 h and during mixing the temperature of the whole system 0921-5107/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2010.01.029