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Fabrication of High-Quality Graphene Oxide Nanoscrolls and Application

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Fabrication of High-Quality Graphene Oxide Nanoscrolls and Application Fan et al. Nanoscale Research Letters (2015) 10:192 DOI 10.1186/s11671-015-0894-3 NANO EXPRESS Open Access Fabrication of high-quality graphene oxide nanoscrolls and application in supercapacitor Tianju Fan1, Wenjin Zeng1, Qiaoli Niu1, Songzhao Tong1, Kaiyu Cai1, Yidong Liu2*, Wei Huang1,2, Yong Min1,3* and Arthur J Epstein3 Abstract We reported a simple and effective way of fabricating one-dimensional (1D) graphene oxide nanoscrolls (GONS) from graphene oxide (GO) sheets through shock cooling by liquid nitrogen. The corresponding mechanism of rolling was proposed. One possibility is the formation of ice crystals during the shock cooling process in liquid nitrogen to be the driving force. The other might be due to the uneven stress of the sheets inside or outside ice during the lyophilization. After reducing, graphene nanoscrolls (GNS) exhibited good structural stability, high specific surface area, and high specific capacitance. The capacitance properties were investigated by cyclic voltammetry, galvanostatic charge-discharge, and electrical impedance spectroscopy. A specific capacity of 156 F/g for the GNS at the current density of 1.0 A/g was obtained comparing with the specific capacity of 108 F/g for graphene sheets. Those results indicated that GNS-based rolling structure could be a kind of promising electrode material for supercapacitors and batteries. PACS: 81.07.De (Nanotubes); 81.16.Be (Chemical synthesis methods); 62.23.Hj (Nanowires); 72.80.Vp (Graphene electronic transport) Keywords: Graphene nanoscrolls; Shock cooling; Supercapacitors Background capillary compression using ultrasonic atomization. In con- Graphene was one-atom-thick carbon material with re- trast to its flat structure that tended to aggregate, the crum- markable electronic, mechanical, and thermal properties pled graphene spheres feature had high surface area and [1,2]. It can be viewed as a fundamental two-dimensional remarkable stability against aggregation [8]. These three- (2D) building block for an array of nanostructures. Geim dimensional (3D) bulkyball structures had demonstrated et al. described that graphene can be wrapped up into zero- promising applications in energy conversion and storage dimensional (0D) buckyballs or rolled into one-dimensional devices [9,10]. Most of the produced carbon nanoscrolls nanotubes [3]. In fact, theoretical studies have long pre- (CNS) were rolled up by thin graphite. Recently, graphene dicted that individual graphene sheets with high elasticity sheet (GS)-wrapped CNS with high quality were reported can undergo rapid conformational changes, which resulting by using isopropyl alcohol solution to roll up monolayer, in the formation of nanoscale sandwiches, buckyball, knots, but this method suffers from complicated procedures and and tubes via folding, crumpling, sliding, and rolling [4]. low yield and throughput [11]. Therefore, the rapid devel- Currently, only two of the predicted structures (buckyball opment of graphene nanoscrolls (GNS) was still hindered [5] and nanoscroll [6,7]) have been reported. Graphene by lacking of a simple and effective method to produce nanosheets were easily crumpled into ball-like structures by high-purity and high-quality GNS in high yield. Another interesting one-dimensional (1D) tubular structure, CNS were formed by rolling up of flat graphite * Correspondence: [email protected]; [email protected] thin nanoplates [12], attracted intensive investigations as 2State Key Laboratory of Organic Electronics and Information Displays and Fountain Global Photoelectric Technology Co., Ltd. 2 Xinyue Road, Yancheng, well. Due to their hybrid topology, CNS were expected to Jiangsu 224000, China possess some unique physiochemical properties distinct 1Institute of Advanced Materials, Nanjing University of Posts and from those of graphene and carbon nanotubes (CNTs). Telecommunications, 9 Wenyuan Road, Nanjing, Jiangsu 210046, China Full list of author information is available at the end of the article © 2015 Fan et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. Fan et al. Nanoscale Research Letters (2015) 10:192 Page 2 of 8 Theoretical calculations predicted that CNS were a oxide was dispersed in water to form graphene oxide promising candidate for hydrogen storage as they had a dispersion (0.84 mg/mL, 80 mL) in a 100-mL beaker more accessible surface than CNTs [13,14]. In addition, which was rapidly cooled by surrounding with liquid ni- the CNS possess a tunable interplanar distance by trogen. The water was removed by freeze-drying ma- intercalation or doping. It had also been found that chine. The remaining GONS (0.24 g) was dispersed in CNS were suitable as electrodes for supercapacitors water (150 mL) and reduced by sodium nitrite (0.34 g) [15] and batteries [16,17]. However, due to our limited in a 250-mL round-bottom flask, which was then heated knowledge of this new material, the research on the to 90°C for 2 h, the water was removed, and the residue aforementioned graphene architectures (from graphene was washed by water to obtain GNS. to nanoscroll) was limited mainly on theoretical predic- tions. Most of the predicted graphene architectures had Characterization not been produced experimentally. Scanning electron microscope (SEM) images were ob- In this work, we reported the graphene oxide nanosc- tained by a high-resolution scanning electron micro- rolls (GONS) of a distinct form of 1D tubular graphene scope (JEOL, JSM-7401, JEOL Ltd., Akishima-shi, Japan) architecture, which fabricated by shock cooling of aque- at 3.0 kV. Transmission electron microscopy (TEM) ex- ous graphene oxide (GO) dispersion by liquid nitrogen. periments were performed on a high-resolution trans- The resulting stable and curly 1D structure was found mission electron microscope (JEOL, TEM, exited at to be high specific surface area and high specific capaci- 100 kV, JEOL Ltd., Akishima-shi, Japan) equipped with tance. As a consequence, a high reversible capacity, selected area electron diffraction (SAED). X-ray diffrac- good thermal stability and good rate capability, and ex- tion (XRD) was recorded on a Rigaku D/Max-RB dif- cellent cyclic stability were achieved. fractometer (Rigaku Corporation, Tokyo, Japan) with CuKα radiation at 40 kV and 120 mA. Thermogravimet- Methods ric analysis (TGA) was carried out using a thermogravi- Chemicals and materials metric analyzer (METTLER TOLEDO, TGA/DSC-1, Graphite powder (400 mesh) was obtained from Beijing Mettler-Toledo GmbH, Switzerland) from 30°C to 600°C −1 Chemical Reagents (Beijing, China). KMnO4,NaNO2, at a heating rate of 10°C min in N2. Raman spectra were NaOH, concentrated H2SO4, concentrated HCl, and characterized by a JY Horiba Raman (Aramis, Horiba, H2O2 (30%) were all analytical grade and purchased Ltd., Minami-ku Kyoto, Japan) under 514-nm laser for from Shanghai Sinopharm Chemical Reagent Co., Ltd the accumulation intensity of three-time scan. (Shanghai, China). All aqueous solutions were prepared with ultrapure water (18 MΩ). Capacitance performance test Capacitance performances of GNS materials were tested Preparation of graphene oxide by cyclic voltammetry (CV), galvanostatic charge/dis- GO is prepared by the modified hummers method [18]. charge, and electrochemical impedance spectroscopy (on Briefly, 1.0 g of graphite and 60 mL H2SO4 (98%) was a CHI 660E, CH Instruments, Inc., Bee Cave, TX, USA). stirredinanicebath,and5.8gKMnO4 was slowly All of the electrochemical experiments were carried out added with stirring for 0.5 h. The solution is heated to in a three-electrode system. The fabrication of working 30°C for 2 h, 40 mL of deionizer water is added slowly, electrodes was carried out as follows. GNS (4.2 mg) were the reaction is heated to 90°C for 30 min, then, 80 mL mixed with carbon black and poly (tetrafluoroethylene) of deionizer water is added. When the temperature is at a mass ratio of 85:10:5 in several drops of ethanol. cooled to 60°C, 10 mL H2O2 (30%) is added to give an The working electrode was formed after drying. The po- orange yellow solution. Two hundred milliliters of 5% tential range of CV examination was −0.2 to 1.0 V, and HCl solution is added, decanted the supernatant, and that of galvanostatic charge/discharge tests was 0 to centrifuged with deionizer water to pH 4 to 6, and the 1.0 V. Electrochemical impedance spectroscopy (EIS) mixture solution is further dialyzed in a dialysis bag in tests were performed in the frequency range of 105 to 2 days, and low density large graphene oxide is obtained. 0.05 Hz at 10-mV amplitude referring to open-circuit potential (OCP). Cycling stability of the materials was Preparation of GNS performed on galvanostatic charge/discharge curves at GO was produced by the modified Hummers method current density of 1 A/g after 2,000 cycles. through acid oxidation of flake graphite. The primary graphite was suspended in water under sonication for Results and discussion 1 h, which followed by centrifugation at 4,000 rpm for Mechanism for the formation of GONS 30 min and dispersed in the water. The resulting yellow The transformation from 2D graphene sheet into the mixture was cooled to room temperature. Graphene curly tubular 1D structure could be understood with the Fan et al. Nanoscale Research Letters (2015) 10:192 Page 3 of 8 aid of the illustrations in Figure 1. GO sheets was pre- exposed in the air while the other was still remaining in- pared by the chemical exfoliation from graphite. Initially, side ice. GO maintained flat sheets containing functional groups of carboxyl, hydroxy, and epoxy (Figure 1a). The hydro- Structure of the GONS philic groups on GO surface result its good dispersibility Figure 2a,b showed a SEM image of GO sheets exfoliated in aqueous solution. GO was dispersed in water to ob- from graphite.
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