Paper-like graphene-Ag composite films with enhanced mechanical and electrical properties
© Gao et al; licensee Springer. 2013
Received: 2 January 2013
Accepted: 13 January 2013
Published: 17 January 2013
In this paper, we have reported that paper-like graphene-Ag composite films could be prepared by a facile and novel chemical reduction method at a large scale. Using ascorbic acid as a reducing agent, graphene oxide films dipped in Ag+ aqueous solutions can be easily reduced along with the decoration of different sizes of Ag particles distributed uniformly. The results reveal that the obtained films exhibit improved mechanical properties with the enhancement of tensile strength and Young's modulus by as high as 82% and 136%, respectively. The electrical properties of graphene-Ag composite films were studied as well, with the sheet resistance of which reaching lower than approximately 600 Ω/□. The graphene-Ag composite films can be expected to find interesting applications in the area of nanoelectronics, sensors, transparent electrodes, supercapacitors, and nanocomposites.
KeywordsGraphene Ag particles Composite films Graphene oxide In situ reduction Graphene paper Electrical properties Mechanical properties
Graphene, a two-dimensional single atomic layer of sp 2 -hybridized carbon arranged in a honeycomb structure, has generated tremendous interest due to its unique combination of electronic, mechanical, chemical, and thermal properties [1–4]. Many potential applications in various fields, including filler materials [5, 6], field-emission devices , nanoscale electronic devices , sensors [8–10], transparent electrodes [11–14], and so on [15–18], have been reported.
Large-scale preparation of paper-like graphene films has aroused much attention for their unique mechanical and electrical properties [15, 16, 19–22]. Some methods, including micromechanical exfoliation , chemical vapor deposition [12, 23–25], and self-assembly [26–32] have been used to prepare this fascinating structure of the films, which have great potential for the applications in transparent electrodes , supercapacitors , biosensors , etc. Meanwhile, some noble metal nanoparticles have been added into the graphene films to improve the electronic and electrochemical properties of the composite films [31, 32] using many methods, such as chemical reduction , electrochemical reduction , biochemical reduction , and in situ thermal reduction . As a result, the fabricated composite films have shown a tremendous potential in improving the electrochemical properties  and as an electrode of biosensors .
Although many efforts and applications have been achieved for these novel carbon films, it is still a great challenge to develop a novel method to prepare the films at a large scale. Herein, we report a new method to prepare graphene-Ag composite films with excellent and improved properties, which are fabricated by the large-scale assembly of graphene oxide films, followed by in situ reduction of graphene oxide films together with Ag+ by ascorbic acid. The mechanical and electrical properties of the obtained graphene-Ag composite films are also investigated.
The natural graphite powder (carbon content 99.999%) in the experiment was purchased from Qingdao Tianyuan Carbon Co. Ltd, Qingdao, China. Other solvents and reagents were of analytical reagent grade and used as received.
Preparation of graphene-Ag composite films
Atomic force microscope (AFM) image was taken with the Multimode Nanoscope V scanning probe microscopy system (Veeco Instruments Inc., Plainview, NY, USA) using tapping mode with Picoscan v5.3.3 software. The morphology of the films were observed using a scanning electron microscope (SEM) using a Carl Zeiss ULTRA 55 (Carl Zeiss, Oberkochen, Germany) with energy dispersive X-ray (EDX) spectrometry mode. The crystal structures of the films were examined by X-ray diffraction (XRD; D/MAX-2200, Rigaku, Tokyo, Japan) with Cu Kα (λ = 1.5418 Å) and 2θ from 5° to 85°. The Raman spectra were obtained using a Senterra R200-L Raman spectrometer (Bruker Optik GmbH, Ettlingen, Germany) with a 514-nm line of laser source. Fourier transform infrared (FTIR) spectra were recorded using a Vertex 70 vacuum FTIR spectrometer (Bruker Optik GmbH) and scanned from 4,000 to 400 cm−1 with KBr as background. Thermogravimetric analysis (TGA; Pyris 1, PerkinElmer, Waltham, MA, USA) was performed under a highly pure nitrogen atmosphere with a heating rate of 1°C to 10°C/min from 30°C to 700°C. The films with 5-mm width and 4- to 5-cm length were measured by dynamic mechanical analysis (DMA; TA-Q800, TA Instruments, Newcastle, DE, USA) at the room temperature. A four-probe detector (RTS-8, 4 PROBES TECH, Guangzhou, China) was used to measure the sheet resistance of the films.
Results and discussion
Elements of all films measured by EDX
Atomic ratio (C/O)
Mechanical properties of graphene oxide films and graphene films reduced for different times
1.3 ± 0.2
33.0 ± 1.3
3.3 ± 0.3
(b) 1 h
0.8 ± 0.1
49.3 ± 0.9
6.8 ± 0.1
(c) 5 h
0.9 ± 0.1
60.2 ± 0.6
7.8 ± 0.1
(d) 12 h
0.9 ± 0.1
32.5 ± 1.4
3.9 ± 0.2
In summary, we have demonstrated that graphene-Ag composite films are fabricated in a large scale using a facile chemical reduction method. The graphene oxide sheets can be easily assembled to form free-standing graphene oxide films during the volatilization process on PTFE hydrophobic substrate. After dipping the graphene oxide films into the Ag+ aqueous solution, Ag particles can be uniformly distributed on the surface of graphene films using ascorbic acid as a reducing agent. The morphology of the composite films can be maintained during the reduction process. The obtained films have been characterized by AFM, SEM, XRD, Raman, FTIR, TGA, DMA, and a four-probe detector. The results show that the obtained films exhibit improved mechanical properties with the enhancement of tensile strength and Young's modulus by as high as 82% and 136%, respectively. The electrical properties of the graphene-Ag composite films were studied as well, with the sheet resistance of which reaching lower than approximately 600 Ω/□. The composite films hold a great potential for applications in the fields of nanoelectronics, sensors, transparent electrodes, supercapacitors, and nanocomposites.
This work was supported by the National High-Tech R & D Program of China (863, no. 2011AA050504), National Natural Science Foundation of China (no. 51102164), Program for New Century Excellent Talents in University, Shanghai Science and Technology Grant (12JC1405700 and 12nm0503800), Shanghai Pujiang Program (no. 11PJD011), the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, Medical-Engineering Crossover Fund (YG2012MS40 and YG2012MS37), and Science-Engineering Crossover Fund (X198052) of Shanghai Jiao Tong University. We also acknowledge the analysis support from the Instrumental Analysis Center of Shanghai Jiao Tong University.
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