Functionalized ionic liquid-assisted mechanochemical synthesis of graphene nanosheet/polypyrrole nanocomposites Xiangjun Lu, Wei He, Hui Dou ⁎, Sudong Yang, Liang Hao, Fang Zhang, Laifa Shen, Xiaogang Zhang ⁎ College of Material Science and Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China abstract article info Article history: Received 5 July 2011 Accepted 9 December 2011 Available online 14 December 2011 Keywords: Polypyrrole Graphene nanosheet Polymeric composites Nanocomposites This study describes a simple and effective ionic liquid (IL)-assisted mechanochemical route to prepare a set of nanostructured graphene nanosheet/polypyrrole (GNS/PPy) composites of with different PPy loading. The functionalized IL 1-butyl-3-methylimidazolium tetrachloroferrate (Bmim[FeCl 4 ]) used here acts as not only the dispersant of GNS but also the catalyst and dopant in the synthesis of PPy. FTIR illustrates the presence of PPy in the composites. A comparative study performed on composites and pure PPy has led to two main conclusions: on one hand, the microstructure of the GNS/PPy composites is dependent on the loading of PPy. On the other hand, GNS/PPy composites show improved conductivity and thermal stability compared with pure PPy. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Polypyrrole (PPy) with excellent atmospheric stability, good bio- compatibility and convenient preparation is one of the most promis- ing conducting polymers and can be exploited in various applications. However, PPy also has some inevitable disadvantages, that is, weak mechanical property and low electronic conductivity in dedoping state. Recently, the combination of graphene nanosheet (GNS) with extraordinary electrical and mechanical properties and PPy has re- ceived much attention to improve its mechanical, electrical and elec- trochemical properties [1–3]. Nevertheless, the aggregation of GNS is a great challenge to synthesize GNS/PPy composite with a uniform structure. Ionic liquid (IL) consisting of a pair of cation and anion is regarded as a new class of dispersants for GNS [4]. The shielding effect of IL on the π–π stacking interactions among GNS takes the key role in dis- persing GNS, and thus the dispersing of GNS with IL has less effect on the characteristics of GNS. Significantly, the tunability of the chem- ical structures of IL (including anions, cations or their combination) can be expected to form functionalized IL. From this viewpoint, mag- netic ionic liquid (MIL) has been developed [5]. The difference be- tween MIL and conventional IL is that the anion of MIL is FeCl 4 - . Conducting polymers (PPy [6], poly(3,4-ethylenedioxythiophene) [7] and poly(3-methyl thiophene) [8]) were successfully synthesized in the presence of 1-butyl-3-methylimidazolium tetrachloroferrate (Bmim[FeCl 4 ]), in which the FeCl 4 - moiety acts as synthetic catalyst and dopant of conducting polymers. Such a unique chemical structure prompts us to explore Bmim[FeCl 4 ] as a dispersant of GNS and syn- thetic catalyst and dopant of PPy in preparing uniform GNS/PPy composite. 2. Experimental section The Bmim[FeCl 4 ] (molecular structure showing in Fig. 1a) was synthesized according to previous report [5]. GNS was prepared by 1-octyl-3-methyl-imidazolium tetrafluoroborate ([C 8 MIM][BF 4 ])- assisted electrochemical synthesis (the obtained C 8 MIM-functiona- lized GNS was abbreviated as GNS CM ) [9]. 30 mg GNS CM , 2 g Bmim [FeCl 4 ] and agate grinding balls (six with a diameter of 1 cm and four with a diameter of 0.5 cm) were placed in a 50 mL agate grinding bowl. The bowl was spun at 400 rpm in a planetary micromill for 1 h and then the mixture turned into a black gel. The IL gel could be ex- truded from a needle tube and formed a cable-like material that was not torn apart when suspended (Fig. 1b). Pyrrole (0.3 g) was added and the mixture was milled for another 0.5, 2 and 12 h, respec- tively. The products were rinsed several times with distilled water and ethanol. The mass of PPy in GNS CM /PPy composites for 0.5, 2 and 12 h was 35, 65 and 90 wt.%, respectively by calculating the weight difference between the final products and GNS CM (The sam- ples were denoted as G CM Py35, G CM Py65 and G CM Py90, respectively). PPy was synthesized by the same procedure described above but without GNS CM . FTIR spectra were recorded with a Model 360 Nicolet AVATAR. The morphology was investigated by LEO1530 SEM. Electri- cal conductivity was measured by conventional four-probe DC meth- od. TGA measurements were carried out under nitrogen flow with a NETZSCH STA 409 PC system TG Analyzer (10 °C min -1 ). Materials Letters 71 (2012) 57–59 ⁎ Corresponding authors. Tel.: + 86 025 52112918; fax: + 86 025 52112626. E-mail addresses: dh_msc@nuaa.edu.cn (H. Dou), azhangxg@nuaa.edu.cn (X. Zhang). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.12.037 Contents lists available at SciVerse ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/matlet