Current Opinion in Solid State and Materials Science 12 (2008) 9–13
Contents lists available at ScienceDirect
Current Opinion in Solid State and Materials Science journal homepage: www.elsevier.com/locate/cossms
Preparation and characterization of conducting polyaniline/silica nanosheet composites Peng Liu * State Key Laboratory of Applied Organic Chemistry, Institute of Polymer Science and Engineering, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, PR China
a r t i c l e
i n f o
Article history: Received 11 November 2008 Accepted 6 January 2009
Keywords: Polyaniline Silica nanosheets Nanocomposite Electrical conductivity
a b s t r a c t A series of polyaniline/silica nanosheet composites (PANI/SNS) with different contents of the silica nanosheets derived from vermiculite via acid-leaching were prepared via the in situ chemical oxidation polymerization. The PANI/SNS composites were characterized with Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and electrical conductivity measurement. It is interesting that the electrical conductivities of the PANI/SNS composites increased with the increasing of the contents of the silica nanosheets added because of the moisture absorption. It was conﬁrmed by the TGA analysis. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Polyaniline (PANI) has been known as one of the most technologically important conducting polymers because of its high electrical conductivity, easy producibility, environmental stability, easy preparation, and relatively low cost . It has attracted much attention in recent years due to its potential applications in various hi-tech aspects, for example, in electrochemical displayers, sensors, catalysis, redox capacitors, electromagnetic shielding as well as in secondary batteries [2–6]. In the past few years, nanocomposites based on polyaniline have been harvesting several intriguing properties within themselves due to the mutual inﬂuence of the individual constituents and synergism of their properties . In the reported polyaniline based nanocomposites, the inorganic nanoparticles (oxides [8–11] and metals [12–15]), nanosheets [16–25], nanotubes [26–30], nanobelts [31,32], and nanorods [33,34] were also used for the polyaniline based nanocomposites. Compared to other inorganic nanomaterials (nanoparticles, nanotubes, nanobelts and nanorods), the nanosheets have only one dimension (their thicknesses) in nanoscale. The most used inorganic nanosheets, the layered silicates and oxides, were nonconductor. So the research and developments on the electrical conductivities of their polyaniline based nanocomposites are attractive. In the present work, the silica nanosheets (SNS), obtained via acid-leaching of vermiculite, were used for the polyaniline based nanocomposites. The products, PANI/SNS composites were charac* Tel.: +86 931 8912516; fax: +86 931 8912582. E-mail address: [email protected]
1359-0286/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.cossms.2009.01.001
terized with FT-IR, SEM, XRD, TGA, and electrical conductivity measurement. The effect of the amounts of the silica nanosheets added on the electrical conductivities of the PANI/SNS composites was investigated. 2. Experimental 2.1. Raw materials and reagents Vermiculite used was purchased from Xinjiang, China. Vermiculite was pretreated with hydrochloric acid according to a reported patent . 25 g of 250-mesh crude vermiculite was added into a 1-L polypropylene beaker containing 800 mL of 2 M HCl solution at room temperature. The resulting slurry was magnetically stirred for 12 h. The product was separated by ﬁltration and then washed thoroughly with distilled water several times until the ﬁltrate had a pH value of 7.0. Then the silica nanosheets obtained were stored as aqueous suspension for the further use. Aniline, ammonium persulfate (APS), and other solvents used were all analytical grade reagents of Tianjin Chemicals Co. Ltd., China, and used without any pre-treatment. Distilled water was used throughout. 2.2. Preparation of the PANI/SNS composites Certain amount of the silica nanosheets suspension (including 0.23 g silica nanosheets/10 ml), aniline (9.313 g, 0.10 mol), and 10 ml conc. HCl were added into 200 ml water with stirring in ice-water bath. The mixtures were stirred for further 30 min to ensure that the mixtures were cooled to 0 °C. Then 100 ml aqueous
P. Liu / Current Opinion in Solid State and Materials Science 12 (2008) 9–13
solution of APS (containing APS 22.820 g, 0.10 mol) was dropped into the emulsions in 60 min. The mixture was stirred for another 4 h in ice-water bath. The products, PANI/SNS composites with different amounts of the silica nanosheets (1.0–4.0% weight ratios to aniline) (Table 1) were ﬁltered and washed with water and ethanol each for three times in turn. Finally they were dried at 40 °C for 24 h under vacuum. 2.3. Analysis and characterization Elemental analysis (EA) of C and N was performed on Elementar vario EL instrument. The chemical structure of the PANI/SNS powders were conducted by recording infrared spectra using NEXUS 670 (Nicolet) in the range of 400–4000 cm 1 with the resolution of 4 cm 1. The KBr pellet technique was adopted to prepare the
Table 1 Preparation conditions of the PANI/SNS composites. Samples
Water (ml) Aniline (mol) HCl (mol) APS (mol) SNS (g) Products (g)
200 0.10 0.10 0.10 0 8.24
200 0.10 0.10 0.10 0.093 7.32
200 0.10 0.10 0.10 0.186 7.14
200 0.10 0.10 0.10 0.279 7.42
200 0.10 0.10 0.10 0.372 7.57
sample for recording the IR spectra. The XRD patterns were recorded in the range of 2h = 10–80° by step scanning with a Shimadzu XRD-6000 X-ray diffractometer. Nickel-ﬁlter Cu Ka radiation (k = 0.15418 nm) was used with a generator voltage of 40 kV and a current of 30 mA. The morphology of the silica nanosheets was characterized with a JEM-1200 EX/S transmission electron microscope (TEM). The silica nanosheets suspended colloid solution was deposited on a copper grid covered with a perforated carbon ﬁlm. The Zeta potentials of the silica nanosheets at different pH values were determined with Zetasizer Nano ZS (Malvern Instruments Ltd, UK). The thermal stabilities of the PANI/SNS powders were determined with Shimadzu ZRY-2P at heating rate of 10 °C/ min from room temperature to 700 °C under N2 atmosphere. The surface morphologies of the PANI/SNS powders were observed using scanning electron microscopy (SEM) (XL-20, Philips Corporation, the Netherlands), operating at 25 kV. The electrical conductivities of the PANI/SNS powders were measured using SDY-4 FourPoint Probe Meter at ambient temperature employing the method on a pressed pellet. 3. Results and discussion 3.1. Silica nanosheets The preparation of the silica nanosheets via acid-leaching of vermiculite was reported in our previous work . After a contact
Fig. 1. SEM images.
P. Liu / Current Opinion in Solid State and Materials Science 12 (2008) 9–13
Fig. 2. TEM images of the silica nanosheets.
the silica nanosheets were negative charged. So the monomer, aniline, might adsorbed onto their surfaces as anilinium chloride salt  before the addition of the oxidant. 3.2. PANI/SNS composites
Fig 1. (continued)
time of 12 h with 2.0 M HCl, the diffraction peaks at 7.3° of the vermiculite was missing. This indicated that the silicate was delaminated and the platelets of vermiculite were less than tens cells or layers of single crystals. The silica nanosheets (Fig. 1 b) showed ordered layered structures compared with the pristine vermiculite (Fig. 1a) from SEM analysis. The terrace structure of the silica nanosheets was observed by TEM (Fig. 2). The silica nanosheets showed the negative zeta potential in the studied pH range (pH 2.0–12.0). This indicated that the surfaces of
The preparation parameters, including the amount of the silica nanosheets, aniline, and the concentration of hydrochloric acid in solution, are given in Table 1. One could found that the conversion of the monomer decreased with the increasing of the amount of the silica nanosheets. From the SEM images (Fig. 1d–g), the morphologies of the PANI/SNS composites containing the silica nanosheets 1.0–3.0% were similar to the pure PANI (Fig. 1c). This indicates that the silica nanosheets had been covered and encapsulated by the polyaniline matrices. However, some uncovered silica nanosheets were found when 4.0% weight ratio of the silica nanosheets added. Fig. 3 shows the FT-IR spectrum of PANI/SNS 4 composites containing 4.0% of the silica nanosheets. The characteristic peaks at about 1460 and 1600 cm 1 are assigned to the [email protected]
stretching modes of the benzenoid ring and the quinoid ring, respectively. The peak at 1250 cm 1 is corresponded to CAN stretching vibration of the secondary aromatic amine. These results are in good agreement with previous spectroscopic characterizations of PANI. The band at 3425 and 3230 cm 1 is attributable to NAH and OAH stretching mode. The peak at 1100 cm 1 is attributable to SiAO vibration of the silica nanosheets. This conﬁrms the incorporation of the silica nanosheets in polyaniline matrix using in situ polymerization method for nanocomposite preparation. Fig. 4 shows the XRD patterns of PANI and PANI/SNS composites. The patterns of PANI exhibit two broad peaks at 2h = 21° and 26°, which can be ascribed to periodicity parallel and periodicity perpendicular to the polymer chain, respectively . There was no new peaks appeared. Therefore no additional crystalline order is introduced into the nanocomposites, and the crystalline behavior of PANI is not affected much by the amorphous silica nanosheets. 3.3. Electrical conductivities and TGA The conductivities of nanocomposites were found to increase from 1.16 to16.67 X 1 cm 1 with the increasing of the silica nano-
P. Liu / Current Opinion in Solid State and Materials Science 12 (2008) 9–13
98 96 94 92 90 88 86 84 82 4000
Wavenumber (cm )
Fig. 3. FT-IR spectrum of the PANI/SNS 4.
280 260 240 220 200 180 160 140 120 100 80 60 40 20 0
Silica/PANI 4 Silica/PANI 3
Novel polyaniline based nanocomposites combined with the silica nanosheets obtained via acid-leaching of vermiculite were prepared via the in situ chemical oxidative polymerization. The addition of the silica nanosheets did not damage the backbone structure of PANI. The conductivities of PANI/SNS composites are higher than that of pure PANI, and are enhanced with the increase in the SNS/monomer mass ratio because of the moisture absorption. It is expected the PANI/SNS composites could be used as sensors for moisture.
Silica/PANI 1 PANI
Theta-2Theta (deg) Fig. 4. XRD patterns of PANI and PANI/SNS composites.
PANI PANI/SNS 1 PANI/SNS 2 PANI/SNS 3 PANI/SNS 4
TGA analysis (Fig. 5). The weight losses around 100 °C increased with the increasing of the silica nanosheets added in the composites. The weight losses were attributed to the release of the moisture absorption. So the increase of the electrical conductivities could be attributed to the moisture absorption which content was higher when the more silica nanosheets added. However, the conductivities of the PANI/SNS nanocomposites prepared in this work were lower than some PANI/layered nanocomposites reported. For example, the conductivities of the PANI/ layered clay nanocomposites were higher than that of the pure PANI . It had been explained that the PANI chains intercalated into the layers were more extended. So the conductivities were enhanced although the nonconductors were added. In the present work, the silica nanosheets were dispersed intricately in the nanocomposites, as shown in Fig. 1. The PANI chains were not intercalated into the layers of the SNS so they were not extended as in the PANI/layered clay nanocomposites. And the silica nanosheets only disrupted the three-dimensional organization of the polymer chains. Furthermore, the dopant, HCl, might escape during the post-treatments of the samples, such as washing and drying. So the lower conductivities were resulted. In the TGA analysis of the nanocomposites, it was found that the presence of the silica nanosheets had not improved the thermal stability of polyaniline obviously. Similar results were obtained by the PANI/red mud nanocomposites . It might due to the inﬂuence of the silica nanosheets on the polymerization and structures of the conducting polymer.
70 60 50 40 30 100
Temperature (deg) Fig. 5. TGA curves.
sheets weight ratios from 0% to 4.0% (Table 1). It is interesting that the electrical conductivities increased with the increasing of the nanosheets in the polyaniline based nanocomposites combined with nonconductor nanosheets. This could be explained with the
 Gospodinova N, Terlemezyan L. Conducting polymers prepared by oxidative polymerization: polyaniline. Prog Polym Sci 1998;23:1443–84.  Kang ET, Neoh KG, Tan KL. Polyaniline: A polymer with many interesting intrinsic redox states. Prog Polym Sci 1998;23:277–324.  Patil AO, Heeger AJ, Wudl F. Optical properties of conducting polymers. Chem Rev 1988;88:183–200.  Nakajima T, Kawagoe T. Polyaniline: Structural analysis and application for battery. Syn Metal 1989;28:629–38.  Tahir ZM, Alocilia EC, Grooms DL. Polyaniline synthesis and its biosensor application. Biosens Bioelectr 2005;20:1690–5.  Yang CH, Chih YK, Wu WC, Chen CH. Molecular assembly engineering of selfdoped polyaniline ﬁlm for application in electrochromic devices. Electrochem Solid-State Lett 2006;9:C5–8.  Sezer E. Conducting nanocomposite systems. In: Erokhin V, Ram M, Yavuz O, editors, The New Frontiers of Organic and Composite Nanotechnology, Elsevier, 2008; p. 143–235..  Schnitzler DC, Meruvia MS, Hummelgen IA, Zarbin AJG. Preparation and characterization of novel hybrid materials formed from (Ti, Sn)O2 nanoparticles and polyaniline. Chem Mater 2003;15:4658–65.  Xu P, Han XJ, Jiang JJ, Wang XH, Li XD, Wen AH. Synthesis and characterization of novel coralloid polyaniline/BaFe12O19 nanocomposites. J Phys Chem C 2007;111:12603–8.  Liu P, Liu WM, Xue QJ. In situ chemical oxidative graft polymerization of aniline from silica nanoparticles. Mater Chem Phys 2004;87:109–13.  Zhang LX, Liu P, Su ZX. Preparation of PANI–TiO2 nanocomposites and their solid-phase photocatalytic degradation. Polym Degrad Stab 2006;91:2213–9.  Sivakumar M, Gedanken A. A sonochemical method for the synthesis of polyaniline and Au–polyaniline composites using H2O2 for enhancing rate and yield. Syn Metal 2005;148:301–6.
P. Liu / Current Opinion in Solid State and Materials Science 12 (2008) 9–13  Oliveira MM, Castro EG, Canestraro CD, Zanchet D, Uqarte D, Roman LS, et al. A simple two-phase route to silver nanoparticles/polyaniline structures. J Phys Chem B 2006;110:17063–9.  Houdayer A, Schneider R, Billaud D, Ghanbaja J, Lambert J. New polyaniline/ Ni(0) nanocomposites: Synthesis, characterization and evaluation of their catalytic activity in Heck couplings. Syn Metal 2005;151:165–74.  Pillalamarri SK, Blum FD, Tokuhiro AT, Bertino MF. One-pot synthesis of polyaniline-metal nanocomposites. Chem Mater 2005;17:5941–4.  Kim BH, Jung JH, Hong SH, Joo J, Epstein AJ, Mizoguchi K, et al. Nanocomposite of polyaniline and Na+-montmorillonite clay. Macromolecules 2002;35:1419–23.  Lu J, Zhao XP. Electrorheological properties of suspensions based on polyaniline-montmorillonite clay nanocomposite. J Mater Res 2002;17:1513–9.  Yang SM, Chen KH. Synthesis of polyaniline-modiﬁed montmorillonite nanocomposite. Syn Metal 2003;135–136:51–2.  Wu CS, Huang YJ, Hsieh TH, Huang PT, Hsieh BZ, Han YK, et al. Studies on the conducting nanocomposite prepared by in situ polymerization of aniline monomers in a neat (aqueous) synthetic mica clay. J Polym Sci: Polym Chem 2008;46:1800–9.  Zeng QH, Wang DZ, Yu AB, Yu GQ. Synthesis of polymer-montmorillonite nanocomposites by in situ intercalative polymerization. Nanotechnology 2002;13:549–53.  Yang G, Hou WH, Feng XM, Jiang XF, Guo J. Density functional theoretical studies on polyaniline/HNb3O8 layered nanocomposites. Adv Funct Mater 2007;17:3521–9.  Zhang DH, Qin JG, Yakushi K, Nakazawa Y, Ichimura K. Preparation of a new nanocomposite of conducting polyaniline into layered MnPS3. Mater Sci Eng A 2000;286:183–7.  Huguenin F, Ferreira M, Zucolotto V, Nart FC, Torresi RM, Jr Oliveria, et al. Molecular-level manipulation of V2O5/polyaniline layer-by-layer ﬁlms to control electrochromogenic and electrochemical properties. Chem Mater 2004;16:2293–9.  Bourdo S, Li ZR, Boros AS, Watanabe F, Viswanathan T, Pavel I. Structural, electrical, and thermal behavior of graphite-polyaniline composites with increased crystallinity. Adv Funct Mater 2008;18:432–40.
 Liu DF, Du XS, Meng YZ. Facile synthesis of exfoliated polyaniline/vermiculite nanocomposites. Mater Lett 2006;60:1847–50.  Zengin H, Zhou W, Jin J, Czerw R, Smith Jr DW, Echegoyen L, et al. Carbon nanotube doped polyaniline. Adv Mater 2002;14:1480–3.  Sainz R, Benito AM, Martínez MT, Galindo JF, Sotres J, Baró AM, et al. Soluble self-aligned carbon nanotube/polyaniline composites. Adv Mater 2005;17:278–81.  Zhi CY, Bando Y, Tang CC, Honda S, Sato K, Kuwahara H, et al. Characteristics of boron nitride nanotube-polyaniline composites. Angew Chem Int Ed 2005;44:7929–32.  Small WR, Panhuis M. Inkjet printing of transparent, electrically conducting single-walled carbon-nanotube composites. Small 2007;3:1500–3.  Zhang L, Wang TM, Liu P. Polyaniline-coated halloysite nanotubes via in-situ chemical polymerization. Appl Surf Sci 2008;255:2091–7.  Xu J, Li XL, Liu JF, Wang X, Peng Q, Li YD. Solution route to inorganic nanobeltconducting organic polymer core-shell nanocomposites. J Polym Sci: Polym Chem 2005;43:2892–900.  Song GP, Han J, Guo R. Synthesis of polyaniline/NiO nanobelts by a selfassembly process. Syn Metal 2007;157:170–5.  Dutta K, De S, De SK. Optical and electrical characterizations of self-assembled CdS nanorods-polyaniline composites. J Appl Phys 2007;101:p093711.  Liu YS, Liu P, Su ZX. Core-shell [email protected]
composite particles via in situ oxidative polymerization. Syn Metal 2007;157:585–91.  Rittler HR. Method of treating phyllosilicates. U.S. Patent 1990; 4,952,388.  Zhao MF, Tang ZB, Liu P. Removal of methylene blue from aqueous solution with silica nano-sheets derived from vermiculite. J Hazard Mater 2008;158:43–51.  Zhang ZM, Wei ZX, Wan MX. Nanostructures of polyaniline doped with inorganic acids. Macromolecules 2002;35:5937–42.  Wu Q, Xue Z, Qi Z, Wang F. Synthesis and characterization of PAn/clay nanocomposite with extended chain conformation of polyaniline. Polymer 2000;41:2029–32.  Gok A, Omastova M, Prokes J. Synthesis and characterization of red mud/ polyaniline composites: Electrical properties and thermal stability. Eur Polym J 2007;43:2471–80.