Synthesis and characterization of nanocomposites based on polyaniline-gold/graphene nanosheets
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Polymer nanocomposites (NSPANI/AuNP/GR) based on nanostructured polyaniline, gold nanoparticles (AuNP) and graphene nanosheets (GR) have been synthesized using in situ polymerization. A series of nanocomposites have been synthesized by varying the concentration of GR and chloroauric acid to optimize the formulation with respect to the electrochemical activities. Out of these series of NSPANI/AuNP/GR nanocomposites, it has been found that only one particular nanocomposite has the best electrochemical properties, as analyzed by cyclic voltammetry (CV) and differential pulse voltammetry and conductivity. The best nanocomposite has been characterized by Fourier transform infrared Raman spectroscopy, UV–vis spectroscopy, X-ray diffraction studies, transmission electron microscopy, scanning electron microscopy and atomic force microscopy. The CV of the best nanocomposites show the well-defined reversible redox peaks characteristic of polyaniline, confirming that the polymer maintains its electro activity in the nanocomposites. Another nanocomposite has been prepared with identical composition (as found with the best nanocomposite) by mixing of pre-synthesized nanostructured polyaniline with chloroauric acid and graphene dispersion in order to predict the mechanism of in situ polymerization. It is inferred that the nanocomposite prepared by blending technique loses its property within 48 h indicating phase separation whereas the nanocomposite prepared by in situ technique is highly stable.
KeywordsPolyaniline nanocomposite Graphene nanosheet Gold nanoparticles Electrochemical properties
In recent years, conductive polymers synthesized in the form of nanostructures are of particular interest since their unique morphology with high specific surface area usually results in very exclusive advantages such as improved dispersion (Li et al. 2007) in organic and inorganic solvents, enhanced electronic conductivity (Banerjee and Mandal 1995; Thanpitcha et al. 2008) and response to sensor applications (Virji et al. 2004; Huang et al. 2004). Their synthesis and chemical modification offer unlimited possibilities unlike inorganic metals and semiconductors, which is an advantage with these polymers. It is possible to reduce the structural disorder in doped conducting polymers by choosing optimum parameters during synthesis. It is worthwhile to mention that the nanostructured intrinsically conducting polymers (NSICP) offer reduced structural disorder which consequently helps in increasing the electronic conductivity of the polymers (Bianchi et al. 1999). The nanostructured conducting polyaniline (NSPANI) is unique among the family of conducting polymers because of its ease of synthesis, environmental stability, tunable electronic conductivity, versatile electrochemical switching behavior (Xia et al. 2010), reversible doping/dedoping chemistry(Huang et al. 1986; MacDiarmid 1997; MacDiarmid et al. 1985) excellent mechanical strength, and suitability for making composites with different types of binders, which make it one of the most suitable components in the fabrication of macromolecular electronic devices such as opto and microelectronics, photonics (Holdcroft 2008), sensors in chemical (Virji et al. 2004), electrochemical (Janata and Josowicz 2003; Wang and Chan 2004) and biological applications (Liu et al. 2005). Nanostructured polyaniline has been mainly obtained with the aid of template-guided polymerization within channels of microporous zeolites, electrodes, porous membranes or via chemical routes in the presence of self-organized supramolecules or stabilizers and non-templated routes (Nandi et al. 2007).
Graphene, a two-dimensional sheet of sp2 conjugated atomic carbon, has stimulated intense research interest because of its unique band structure, massless fermions, and ultrahigh carrier mobility (Geim 2009; Tang et al. 2010). These unique properties hold great promise for potential applications in many technological aspects such as nanoelectronics, sensors, nanocomposites, batteries, supercapacitors and hydrogen storage (Li et al. 2008). The high specific surface area of 2,630 m2/g enables it to afford an ultrahigh loading capacity for biomolecules and drugs (Tang et al. 2010; Liu et al. 2008). Recently, graphene has been successfully used in many bioassay applications (Tang et al. 2010; Lu et al. 2010; Dong et al. 2010). Due to the excellent properties of graphene and the advantages of polyaniline, it is most likely chosen to be the conductive polymer backbone for graphene–polymer composites. An important aspect of such graphene-based composite materials is to maintain the graphene sheets as thin as possible and to disperse them homogeneously in the matrix, which is necessary for improving its electrochemical properties. Both electrochemical and chemical methods have been used to synthesize the composite in reported literatures (Wang et al. 2009a, 2010; Murugan et al. 2009). Very recently, Goswami et al. (2011) have focused on the synthesis of composites of PANI-β-camphor sulfonic acid (β-CSA) nanofibers with graphene oxide (GO) and Graphene (GR) and have investigated the cold cathode field emission performance of the same. Bai et al. (2009) employed sulfonated polyaniline and Zhou et al. (2010) developed a synthesis mediated by polymerized ionic liquid for the preparation of stable aqueous dispersions of polyaniline/graphene materials. Some recent studies have already discussed about the structural, optical, electrical and thermal properties of graphene–polyaniline composites and concluded that these composites can be utilized for numerous applications in nanoelectronics, rechargeable batteries, electromagnetic interference (EMI) shielding and many more (Zhang et al. 2010; Wu et al. 2010; Bourdo et al. 2008).
Also, several studies have been performed on the electrochemical properties of metal-doped graphene (Hongkun and Chao 2011; Zhang et al. 2011; Shen et al. 2010) as well as in the area of metal-doped graphene (GR)/conducting polymer (CP) composites (Stoller et al. 2008; Wang et al. 2009b). The metal nanoparticles deposited onto the graphene serve as an efficient catalyst to improve electrochemical performance of the GR/CP and that they resulted in the increase of the charge transfer between GR and CP by bridge effect (Kim et al. 2010). However, there has been limited work in the area of metal-doped NSCP/graphene composites.
Recently, conducting polymer nanocomposites have attracted much attention for their ability to enhance electrical and mechanical properties by synergistic effects through the interaction of the two components. For example, graphene-conducting polymer composites have also become attractive as electrode materials due to their combination effect as low-dimensional organic conductors and a high surface area and excellent conductivity of graphenes. Also, several studies have been performed on the electrochemical properties of metal-doped graphene, whereas there has been limited work in the area of metal/graphene/conducting polymer composites (Stoller et al. 2008; Wang et al. 2009b).
Therefore in the present study, polymer nanocomposites (NSPANI/AuNP/GR) based on nanostructured polyaniline (NSPANI), gold nanoparticles (AuNP) and graphene nanosheets (GR) have been synthesized using in situ polymerization. A series of nanocomposites have been synthesized by varying the concentration of graphene and chloroauric acid to optimize the formulation with respect to the electrochemical activities, conductivity and stable film forming property. Another NSPANI nanocomposite with identical composition was prepared by mixing of pre-synthesized nanostructured polyaniline with chloroauric acid and graphene dispersion in order to predict the mechanism of in situ formation of nanocomposite and to compare the electrochemical properties of both the nanocomposites.
Few layered graphene (Quantum materials corporation, Bangalore), Aniline (Sigma-Aldrich), sodium dodecyl sulphate (SDS) (Qualigen), ammonium persulfate (NH4)2S2O8 (E-Merck), hydrochloric acid (Qualigen), Chloroauric acid HClO4 (Sigma-Aldrich) were used in the present experiment. Deionized water from a Millipore-MilliQ was used in all cases to prepare aqueous solutions. Monomer was double distilled before polymerization.
In situ polymerization
Experimental conditions for the synthesis of samples
Experimental conditions for the synthesis of samples
Nanostructured polyaniline (NSPANI) (ml)
Graphene (GR) (mg)
Gold (HClO4) (μl)
Total time for stirring (h)
7 Added after 15 min
7 Added after 30 min
7 Added after 45 min
7 Added after 1 h
The UV–vis spectrum of the nanocomposites was recorded using a Shimadzu UV-1800 UV–vis spectrophotometer. Morphological imaging was obtained by transmission electron microscope (TEM), using a JEOL JEM-1011 at 80 kV and scanning electron microscope (LEO 440 Model). FT-IR Raman spectra of these samples were recorded using a Varian-FT-IR spectrometer series II. Atomic force microscopy (AFM) was performed by Park Systems XE-70 Atomic Force Microscope in non-contact mode. X-ray analysis was performed using a Rigaku make powder X-ray diffractometer (model RINT 2100) with a Cu target (λ = 1.54059 Å). Cyclic voltammetric study was carried out using Autolab Potentiostat/Galvanostat Model 273A.
Results and discussion
Cyclic voltammetry (CV)
Differential pulse voltammetry (DPV)
We have chosen now NSPANI/AuNP/GR as a best sample and further studied its structure and morphology by FT-IR Raman, XRD, SEM, TEM and AFM to confirm its synthesis.
X-ray diffraction (XRD) studies
By applying this formula, we have calculated the size of nanoparticles as 70 nm.
Scanning electron microscopy
Transmission electron microscopy (TEM)
Atomic force microscopy
Roughness parameters for the nanocomposites
Root mean square roughness Rq (nm)
Average roughness Ra (nm)
Ten point average roughness Rz (nm)
Out of all the depositions, only NSPANI/AuNP/GR film has minimum root mean square roughness, average roughness and ten point average roughness. This shows that NSPANI/AuNP/GR film is homogenous and continuous and it can be further used for any device application.
Comparison of electrochemical activity of NSPANI/AuNP/GR nanocomposite formed by in situ polymerization and blending process
Mechanism of formation
Highest conductivity is obtained for NSPANI/AuNP/Gr nanocomposite (4.31 × 10−5) as is revealed from conductivity measurements (Fig. 4). This data reveal that the polyaniline in the composites is richer in quinoid units than the NSPANI. This also suggests that the chains of the polyaniline deposited on the surface of the graphene have longer conjugation lengths. The π-bonded surface of the graphene might interact strongly with the conjugated structure of polyaniline, especially via the quinoid ring (Quillard et al. 1994). In general, aromatic structures are known to interact strongly with the basal plane of the graphitic surface via π-stacking (Park et al. 2009). The interaction between the quinoid ring of the polyaniline and the graphene may facilitate the charge-transfer process between the components of the system and increase the effective degree of electron delocalization, thereby enhancing the conductivity of the composites (Park et al. 2009). It is expected that Au nanoparticles doped onto polyaniline lead to the bridge effect between graphene and polyaniline, resulting in the improved charge transfer and demonstrating a synergy effect on the electrical properties. This indicates that gold nanoparticles and graphene can serve as effective conducting fillers to enhance the electrical properties of polyaniline (Ma et al. 2008).
Polymer nanocomposites (NSPANI/AuNP/GR) based on nanostructured polyaniline, gold nanoparticles (AuNP) and graphene nanosheets (GR) have been synthesized using in situ polymerization. A series of nanocomposites have been synthesized by varying the concentration of graphene and chloroauric acid to optimize the formulation with respect to the electrochemical activities. Out of these series of NSPANI/AuNP/GR nanocomposites, it has been found that only one particular nanocomposite has the best electrochemical properties, as analyzed by cyclic voltammetry (CV) and differential pulse voltammetric (DPV) techniques and conductivity. The CV of the best nanocomposites show the well-defined reversible redox peaks characteristic of polyaniline, confirming that the polymer maintains its electro activity in the nanocomposites. Furthermore, the best NSPANI/AuNP/GR has shown remarkable enhancement in current density (6.22 × 10−4 A) as compared to NSPANI (9.58 × 10−6 A) and NSPANI/GR (4.54 × 10−5 A) nanocomposite indicating an optimum composite formulation. Another NSPANI nanocomposite has been prepared with identical composition (as found with the best nanocomposite) by mixing of pre-synthesized nanostructured polyaniline with chloroauric acid and graphene dispersion in order to predict the mechanism of in situ formation of nanocomposite. The electrochemical properties of both the nanocomposites has been compared and shown that the nanocomposite prepared by blending technique loses its property within 48 h indicating phase separation whereas the nanocomposite prepared by in situ technique is highly stable. These intriguing features of the nanocomposites make them promising materials for applications in biosensors.
We acknowledge the financial assistance received from the Department of Biotechnology, Govt. of India (Project No BTPR 11123/MD/32/41/2008 DBT). We are thankful to Dr. A. K. Chauhan (Founder President, Amity University, Uttar Pradesh) for providing the platform for research at Amity University Uttar Pradesh and we also offer our sincere thanks to Dr.(Mrs.) Balwinder Shukla, Director General A.S.E.T, Dr. R. P. Singh, Director, AINT and Prof. A. K. Srivastava, Director General, AIB, AUUP for their constant support and encouragement. We are also thankful to Dr. Subhasish Ghosh, Akansha and Pawan, JNU New Delhi for conducting SEM and AFM studies.
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