Preparation of poly(3-hexylthiophene)/graphene nanocomposite via in situ reduction of modified graphite oxide sheets
Introduction
Graphene, well known for its excellent performance such as high conductivity, heat resistance and perfect mechanic properties, has been recognized as one of the most promising carbon materials after the fullerene and the carbon nanotube since its discovery in 2004 by Geim and co-workers [1]. With years of the investigation, graphene has been found to be available to prepare polymer-based composite after some simple and effective modifications. Stankovich et al. first prepared a series of isocyanate-treated graphite oxides (GOs) which can be easily dispersed in strong polar organic solvents such as N,N-dimethylformamide (DMF), 1-methyl-2-pyrrolidinone (NMP) and dimethyl sulfoxide (DMSO) [2]. Yin and co-workers [3], [4], [5] have reported that graphene has its potential to be a novel acceptor material for organic photovoltaic devices. They firstly prepared the modified graphite oxide (mGO)/poly(3-hexylthiophene) (P3HT) composite in 1,2-dichlorobenzene (DCB) and then spin-coated the composite on the indium tin oxide (ITO) glass substrate. This strategy had its own advantage that P3HT was annealed at the same time, which had been proved positive to energy conversion efficiency. However, the mGO can be stable in DCB for only a few minutes even after ultrasonic dispersion, which will prevent it from large scale solution processing in the future.
To make the mGO more stable in the less polar organic solvent like that of carbon nanotubes, there are usually two ways [6]: one is covalent bonding [7], [8], [9], [10], the other is noncovalent bonding [11], [12], [13], [14]. We decide to choose the second strategy because it does not destroy the intrinsic structures of graphene and gives structurally intact graphene with functionalities. Herein, we report a simple and effective approach [15], [16] to improve storage stability of P3HT/mGO in a less polar solvent such as chloroform through an in situ reduction method. In the presence of P3HT, mGOs can be reduced in situ and simultaneously coated with P3HT and then prevent it from aggregation and finally exhibit enhanced storage stability. The P3HT/mGO nanocomposites are also characterized and investigated by means of atomic force microscope (AFM), transmission electron microscope (TEM), photoluminescence (PL), Raman spectra, X-ray photoelectron spectroscopy (XPS), and UV–vis measurements. The preparation, characterization, microstructures, optical, and electrical properties of the resulting P3HT/mGO nanocomposites will be discussed.
Section snippets
Experimental
Poly(3-hexylthiophene) (P3HT) was prepared from 3-hexylthiophene by chemical oxidation polymerization [17]. Graphite oxide (GO) was prepared from natural graphite (Qindao Huatai Co., Ltd., average particle size 4 μm, 99%) by the modified Hummers method [18] and dried for weeks in a desiccator before use. Modified GO (mGO) was prepared according to Stankovich method [2]. Briefly, dried graphite oxide (100 mg) was suspended in anhydrous DMF (30 mL) and treated with phenyl isocyanate (500 mg, Aladdin,
Results and discussion
For comparison, we prepared two kinds of chemical-reduced mGO with or without the presence of P3HT by the same method as described above. Fifteen milligrams of P3HT/re-mGO nanocomposite (P3HT:re-mGO = 90:10, by wt.) and 1.5 mg of pure re-mGO were dispersed in the chloroform. Both of the two samples were allowed to stand for 10 min and their dispersion behaviors are shown in Fig. 2. It is obviously seen that the right one will aggregate and suspend in the chloroform as was reported in the literature
Conclusions
In conclusion, P3HT/re-mGO nanocomposite has been successfully obtained via the methods of in situ reduction of isocyanate-treated graphite oxide in the presence of P3HT. The resulting P3HT/re-mGO nanocomposite materials exhibit good dispersity in chloroform and show high storage stability (>20 days). The method described in this work can be extended to obtain other main-chain conjugated polymer/re-mGO nanocomposites in common organic solvents as well. Further work to achieve this goal is under
Acknowledgements
Support from (1) the National Natural Science Foundation of China (50703029 and 10804072); (2) Shanghai Rising-Star Program (09QA1406300 and 07QA14026), the Foundation of Nano Science Technology Project of Shanghai China (0752nm012 and 0952nm02700), and Key Fundamental Project of Shanghai China (08JC1410400); (3) Key Laboratory of Macromolecular Synthesis and Functionalization, Ministry of Education, Zhejiang University (Grant No. 2009MSF05); and (4) Open Fund of Shanghai Key Laboratory of
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