Synthesis and Characterization of Conducting Self-Assembled

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Synthesis and Characterization of Conducting Self-Assembled Polyaniline Nanotubes/Zeolite Nanocomposite ´ iric´-Marjanovic´,*,† Vera Dondur,† Maja Milojevic´,† Milosˇ Mojovic´,† Gordana C Slavko Mentus,† Aleksandra Radulovic´,‡ Zorica Vukovic´,§ and Jaroslav Stejskal| Faculty of Physical Chemistry, UniVersity of Belgrade, and Institute of General and Physical Chemistry, Studentski Trg 12-16, 11158 Belgrade, Serbia, Department of Catalysis and Chemical Engineering, ICTM, NjegosˇeVa 12, Belgrade, Serbia, and Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republic ReceiVed September 16, 2008. ReVised Manuscript ReceiVed NoVember 4, 2008 Self-assembled conducting, paramagnetic polyaniline nanotubes have been synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in aqueous medium in the presence of zeolite HZSM-5, without added acid. The influence of initial zeolite/aniline weight ratio on the conductivity, molecular and supramolecular structure, paramagnetic characteristics, thermal stability, and specific surface area of polyaniline/zeolite composites was studied. The conducting (∼10-2 S cm-1), semiconducting (3 × 10-5 S cm-1), and nonconducting (5 × 10-9 S cm-1) composites are produced using the zeolite/aniline weight ratios 1, 5, and 10, respectively. The coexistence of polyaniline nanotubes, which have a typical outer diameter of 70-170 nm and an inner diameter of 5-50 nm, accompanied by nanorods with a diameter of 60-100 nm and polyaniline/zeolite mesoporous aggregates, distinct from the morphology of microporous zeolite HZSM-5, was proved in the conducting nanocomposite by scanning and transmission electron microscopies. FTIR spectroscopy confirmed the presence of polyaniline in the form of conducting emeraldine salt and suggested significant interaction of polyaniline with zeolite. The evolution of molecular and supramolecular structure of polyaniline in the presence of zeolite was discussed.

Introduction Intrinsically conducting polymers have received considerable attention owing to their wide potential applications in erasable information storage, shielding of electromagnetic interference, radar-absorbing materials, sensors, indicators, actuators, catalysts, electronic and bioelectronic components, rechargeable batteries, membranes, electrochemical capacitors, electrochromic devices, nonlinear optical devices, light-emitting diodes, and antistatic and anticorrosion coatings.1 Polyaniline (PANI) is one of the most important conducting polymers, frequently studied due to its ease of synthesis by standard chemical or electrochemical oxidative polymerization, low cost, high conductivity, and good environmental and thermal stability.2 PANI exists in various acid-base and redox forms with substantially different chemical and physical properties.3 Only the green emeraldine salt form (Scheme 1) is conducting (∼100 S cm-1). The preparation of bulk quantities of conducting PANI is usually performed by the chemical oxidative polymerization of aniline in aqueous solution in the presence of strong acids (initial pH < 2.0), ammonium * Corresponding author. E-mail: [email protected]. † Faculty of Physical Chemistry, University of Belgrade. ‡ Institute of General and Physical Chemistry. § ICTM. | Academy of Sciences of the Czech Republic. (1) ConductiVe ElectroactiVe Polymers: Intelligent Materials Systems; Wallace, G. G., Spinks, G. M., Kane-Maguire, L. A. P., Teasdale P. R., Eds.; CRC Press: Boca Raton, FL, 2003. (2) (a) MacDiarmid, A. G.; Chiang, J. C.; Richter, A. F.; Epstein, A. J. Synth. Met. 1987, 18, 285. (b) MacDiarmid, A. G.; Yang, L. S.; Huang, W.-S.; Humphrey, B. D. Synth. Met. 1987, 18, 393. (c) Yue, J.; Epstein, A. J.; Zhong, Z.; Gallagher, P. K.; MacDiarmid, A. G. Synth. Met. 1991, 41, 765. (d) Cao, Y.; Smith, P.; Heeger, A. J. Synth. Met. 1992, 48, 91. (e) Kaneto, K.; Kaneko, M.; Min, Y.; MacDiarmid, A. G. Synth. Met. 1995, 71, 2211. (f) Wang, H. L.; MacDiarmid, A. G.; Wang, Y. Z.; Gebler, D. D.; Epstein, A. J. Synth. Met. 1996, 78, 33. (g) Ahmad, N.; MacDiarmid, A. G. Synth. Met. 1996, 78, 103. (h) Dhawan, S. K.; Kurnar, D.; Ram, M. K.; Chandra, S.; Trivedi, D. C. Sens. Actuators, B 1997, 40, 99. (i) Tallman, D. E.; Spinks, G.; Dominis, A.; Wallace, G. G. J. Solid State Electrochem. 2002, 6, 73. (3) Stejskal, J.; Kratochvı´l, P.; Jenkins, A. D. Polymer 1996, 37, 367.

Scheme 1. Polyaniline-Emeraldine Salt Form

peroxydisulfate (APS) being the most frequently used oxidant.4 A granular morphology has invariably been observed for PANI prepared under such conditions. Nowadays, there is great interest in the research of nanostructured conducting PANI because its dispersibility and processability have significantly improved, and its performance is substantially enhanced in many conventional applications in comparison with granular PANI.5 The oxidative polymerization of aniline with APS in aqueous solution starting from alkaline, neutral, and slightly acidic reaction conditions at pH > 4.0 and finishing at pH < 2.0 (falling pH method) has been recognized as a reliable template-free synthetic route to PANI nanotubes.6-18 (4) Stejskal, J.; Gilbert, R. G. Pure Appl. Chem. 2002, 74, 857. (5) (a) Virji, S.; Huang, J.; Kaner, R. B.; Weiller, B. H. Nano Lett. 2004, 4, 491. (b) Huang, J. Pure Appl. Chem. 2006, 78, 15. (6) (a) Zhang, Z.; Wei, Z.; Wan, M. Macromolecules 2002, 35, 5937. (b) Lu, X.; Mao, H.; Chao, D.; Zhang, W.; Wei, Y. Macromol. Chem. Phys. 2006, 207, 2142. (7) (a) Qiu, H.; Wan, M. J. Polym. Sci., Part A: Polym. Chem. 2001, 39, 3485. (b) Qiu, H.; Wan, M.; Matthews, B.; Dai, L. Macromolecules 2001, 34, 675. (c) Zhang, L.; Wan, M. Nanotechnology 2002, 13, 750. (d) Wei, Z.; Zhang, Z.; Wan, M. Langmuir 2002, 18, 917. (e) Long, Y.; Zhang, L.; Ma, Y.; Chen, Z.; Wang, N.; Zhang, Z.; Wan, M. Macromol. Rapid Commun. 2003, 24, 938. (f) Long, Y.; Luo, J.; Xu, J.; Chen, Z.; Zhang, L.; Li, J.; Wan, M. J. Phys.: Condens. Matter 2004, 16, 1123. (g) Xia, H.; Chan, H. S. O.; Xiao, C.; Cheng, D. Nanotechnology 2004, 15, 1807. (h) Pinto, N. J.; Carrioń, P. L.; Ayala, A. M.; Ortiz-Marciales, M. Synth. Met. 2005, 148, 271. (i) Zhang, Z.; Wei, Z.; Zhang, L.; Wan, M. Acta Mater. 2005, 53, 1373. (j) Zhang, L.; Wan, M. Thin Solid Films 2005, 477, 24. (k) Xia, H.; Narayanan, J.; Cheng, D.; Xiao, C.; Liu, X.; Chan, H. S. O. J. Phys. Chem. B 2005, 109, 12677.

10.1021/la8030396 CCC: $40.75  2009 American Chemical Society Published on Web 01/26/2009

Polyaniline Nanotubes/Zeolite Nanocomposite

Conducting PANI nanotubes have been synthesized by the chemical oxidative template-free method in the presence of various inorganic acids,6 sulfonic acids,7,8 carboxylic acids,9-12 polymeric acids,13 sulfonated carbon nanotubes,14 sulfonated dendrons,15 and titanium dioxide.16 The new simplified templatefree method of the synthesis of conducting self-assembled PANI nanotubes by the oxidation of aniline with APS in water without any added acid has recently been created.10,17 This facile and efficient synthetic method not only omits hard-template and posttreatment of template removal, but also simplifies reagents. Conducting PANI/inorganic porous solid composites have been the subject of considerable interest because of their improved mechanical and chemical performance compared with the pure PANI. Among various inorganic porous materials for the development of the PANI/inorganic composites, zeolites have received growing attention during last two decades.19-36 PANI/ zeolite composites were prepared by the oxidation of aniline within the zeolite (Y, HZ, HS, HY, MCM-41, 13X, ZSM-5, β) (8) Janosˇevic´, A.; Círic´-Marjanovic´, G.; Marjanovic´, B.; Holler, P.; Trchova´, M.; Stejskal, J. Nanotechnology 2008, 19, 135606. (9) (a) Yang, Y. S.; Wan, M. X. J. Mater. Chem. 2002, 12, 897. (b) Zhang, L.; Wan, M. AdV. Funct. Mater. 2003, 13, 815. (c) Zhang, L.; Long, Y.; Chen, Z.; Wan, M. AdV. Funct. Mater. 2004, 14, 693. (d) Zhang, L.; Peng, H.; Zujovic, Z. D.; Kilmartin, P. A.; Soeller, C.; Travas-Sejdic, J. Macromol. Chem. Phys. 2007, 208, 1210. (e) Sun, Q.; Deng, Y. Mater. Lett. 2008, 62, 1831. (f) Zujovic, Z. D.; Zhang, L.; Bowmaker, G. A.; Kilmartin, P. A.; Travas-Sejdic, J. Macromolecules 2008, 41, 3125. (g) Petrov, P.; Mokreva, P.; Tsvetanov, C.; Terlemezyan, L. Colloid Polym. Sci. 2008, 286, 691. (h) Sun, Q.; Park, M.-C.; Deng, J. Mater. Chem. Phys. 2008, 110, 276. (10) Konyushenko, E. N.; Stejskal, J.; Sˇedeˇnkova´, I.; Trchova´, M.; Sapurina, I.; Cieslar, M.; Prokesˇ, J. Polym. Int. 2006, 55, 31. (11) Stejskal, J.; Sapurina, I.; Trchova´, M.; Konyushenko, E. N.; Holler, P. Polymer 2006, 47, 8253. (12) Stejskal, J.; Sapurina, I.; Trchova´, M.; Konyushenko, E. N. Macromolecules 2008, 41, 3530. (13) (a) Zhang, L.; Peng, H.; Hsu, C. F.; Kilmartin, P. A.; Travas-Sejdic, J. Nanotechnology 2007, 18, 115607. (b) Zhang, L.; Peng, H.; Kilmartin, P. A.; Soeller, C.; Travas-Sejdic, J. Electroanalysis 2007, 19, 870. (c) Zhang, L.; Peng, H.; Sui, J.; Kilmartin, P. A.; Travas-Sejdic, J. Curr. Appl. Phys. 2008, 8, 312. (14) Wei, Z.; Wan, M.; Lin, T.; Dai, L. AdV. Mater. 2003, 15, 136. (15) Cheng, C.; Jiang, J.; Tang, R.; Xi, F. Synth. Met. 2004, 145, 61. (16) Zhang, L.; Wan, M. J. Phys. Chem. B 2003, 107, 6748. (17) Trchova´, M.; Konyushenko, E. N.; Stejskal, J.; Sˇedeˇnkova´, I.; Holler, P.; ´ Ciric´-Marjanovic´, G. J. Phys. Chem. B 2006, 110, 9461. (18) (a) Chiou, N.-R.; Lee, L. J.; Epstein, A. J. Chem. Mater. 2007, 19, 3589. (b) Ding, H.; Shen, J.; Wan, M.; Chen, Z. Macromol. Chem. Phys. 2008, 209, 864. (19) (a) Enzel, P.; Bein, T. J. Phys. Chem. 1989, 93, 6270. (b) Enzel, P.; Bein, T. J. Chem. Soc., Chem. Commun. 1989, 1326. (c) Bein, T.; Enzel, P. Synth. Met. 1989, 29, El63. (d) Bein, T.; Enzel, P. Angew. Chem., Int. Ed. 1989, 28, 1692. (e) Bein, T.; Enzel, P. Mol. Cryst. Liq. Cryst. 1990, 181, 315. (20) Phani, K. L. N.; Pitchumani, S.; Ravichandran, S. Langmuir 1993, 9, 2455. (21) Chang, T.-C.; Ho, S.-Y.; Chao, K.-J. J. Phys. Org. Chem. 1994, 7, 371. (22) Wu, C.-G.; Bein, T. Science 1994, 264, 1757. (23) Wang, L.; Zhu, D.; Tan, Y. Adsorption 1999, 5, 279. (24) Frisch, H. L.; Song, G.; Ma, J.; Rafailovich, M.; Zhu, S.; Yang, N.-L.; Yan, X. J. Phys. Chem. B 2001, 105, 11901. (25) Sreedhar, B.; Palaniappan, S.; Narayanan, S. Polym. AdV. Technol. 2002, 13, 459. (26) Dalas, E.; Vitoratos, E.; Sakkopoulos, S.; Malkaj, P. J. Power Sources 2004, 128, 319. (27) Ma´rquez, F.; Roque-Malherbe, R.; Duconge´, J.; del Valle, W. Surf. Interface Anal. 2004, 36, 1060. (28) Densakulprasert, N.; Wannatong, L.; Chotpattananont, D.; Hiamtup, O.; Sirivat, A. Mater. Sci. Eng., B 2005, 117, 276. (29) Anunziata, O. A.; Go´mez Costa, M. B.; Sańchez, R. D. J. Colloid Interface Sci. 2005, 292, 509. (30) Chuapradit, C.; Wannatong, L. R.; Chotpattananont, D.; Hiamtup, P.; Sirivat, A.; Schwank, J. Polymer 2005, 46, 947. (31) Maity, A.; Ballav, N.; Biswas, M. J. Appl. Polym. Sci. 2006, 101, 913. (32) Malkaj, P.; Dalas, E.; Vitoratos, E.; Sakkopoulos, S. J. Appl. Polym. Sci. 2006, 101, 1853. (33) Ma, X.; Xu, H.; Li, G.; Wang, M.; Chen, H.; Chen, S. Macromol. Mater. Eng. 2006, 291, 1539. (34) Feng, X.; Yang, G.; Liu, Y.; Hou, W.; Zhu, J.-J. J. Appl. Polym. Sci. 2006, 101, 2088. (35) Vitoratos, E.; Sakkopoulos, S.; Dalas, E.; Malkaj, P.; Anestis, C. Curr. Appl. Phys. 2007, 7, 578. (36) Flores-Loyola, E.; Cruz-Silva, R.; Romero-Garcıá, J.; Angulo-Sańchez, J. L.; Castillon, F. F.; Farıás, M. H. Mater. Chem. Phys. 2007, 105, 136.

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channel system,19,21,22,24,27 by chemical,23,29,31-34 electrochemical,20 emulsion,25 and enzymatic36 oxidative polymerizations of aniline in the presence of zeolites (MCM-41, 13X, β, FUYB, Y), dry mixing of PANI powder with the zeolites (Y, 13X, MCM41, LTA),28,30 and addition of zeolite (Zenith-N, LTN) to the PANI solution.26,35 These hybrid materials were proposed to have potential applications as electronic components,19 as sensors (e.g., for gases or pH),28,30,32,33 as antiferromagnetic materials,24 as cathodes in a primary cell,26 for the curing of epoxy resin,25 and for enhancing the thermal conductivity of zeolite.23 Here we report, for the first time, the synthesis of conducting PANI nanotubes/zeolite nanocomposite, which combines unique properties of one-dimensional PANI nanostructures and PANI/ zeolite hybrid materials, by a self-assembly process without added acid. We expect that this simple and versatile synthetic strategy could provide new opportunities for producing a wide range of other nanocomposites of conducting self-assembled PANI nanotubes and various inorganic materials. Prepared PANI/zeolite composites were characterized by FTIR, UV-visible, and EPR spectroscopies, scanning (SEM) and transmission (TEM) electron microscopies, thermogravimetric analysis, and specific surface area and electrical conductivity measurements. Attention has been focused on the effect of initial zeolite/aniline weight ratio on the structure and physicochemical properties of synthesized PANI/zeolite composites.

Experimental Section Materials. Aniline (p.a., Centrohem, Serbia) was distilled under reduced pressure and stored at room temperature, under argon, prior to use. APS (analytical grade, Centrohem, Serbia) and zeolite HZSM-5 [H6(H2O)16(Al6Si90O192), Zeolyst International, SiO2/Al2O3 ) 30, specific surface area SBET ) 400 m2 g-1, average particle size 1-2 µm] were used as received. Synthesis of PANI Nanotubes/Zeolite HZSM-5 Nanocomposite. A typical procedure for preparing PANI nanotubes/zeolite HZSM-5 nanocomposite was as follows: zeolite HZSM-5 (0.93 g) was dispersed in 20 mL of distilled water, and then aniline (0.93 g; 1.0 × 10-2 mol) and water, up to 25 mL total volume of dispersion, were added. This suspension was stirred for 10 min, and then 25 mL of the aqueous solution containing 2.85 g of APS (1.25 × 10-2 mol) was poured into the zeolite/aniline (w/w ) 1) suspension with constant stirring. The resulting mixture was allowed to react 2 h at room temperature, with stirring. The precipitated PANI-zeolite nanocomposite was then collected on a filter, rinsed with 5 × 10-3 M H2SO4, and dried in vacuo at 60 °C for 3 h. Various weight ratios of zeolite HZSM-5 to aniline were used: 1, 5, and 10, and composites prepared at these ratios are designated as PANIZ-1, PANIZ-2, and PANIZ-3, respectively. For each experiment, the molar ratio of APS to aniline was 1.25 and the amount of zeolite was 0.93 g. As a reference sample, pure PANI was prepared by the same procedure, without zeolite. The pH values of the starting zeolite/aniline suspensions were 6.3, 6.0, and 5.1 for the experiments with zeolite/ aniline weight ratios of 1, 5, and 10, respectively. The polymerization times, tpol, were specified to achieve a final pH value 1.5-1.7, i.e., tpol ) 2 h for pure PANI and PANIZ-1, tpol ) 24 h for PANIZ-2, and tpol ) 48 h for PANIZ-3. A portion of product (pure PANI or PANI/zeolite composite) was treated with an excess of 5% ammonium hydroxide for 3 h, to transform it to base (deprotonated) form, and the resulting precipitate was collected on a filter, rinsed with 5% ammonium hydroxide, and dried in vacuo at 60 °C for 3 h. Characterization. A scanning electron microscope JEOL JSM 6460 LV and a transmission electron microscope Tecnai G2 Spirit (FEI, Brno, Czech Republic) have been used to characterize the morphology of the samples. Powder materials were deposited on adhesive tape fixed to specimen tabs and then ion sputter coated with gold using a BAL-TEC SCD 005 Sputter Coater before SEM measurements. For conductivity measurements, the samples were pressed into pellets, 10 mm in diameter and 1 mm thick, under a

3124 Langmuir, Vol. 25, No. 5, 2009 pressure of 124 MPa using a hydraulic press. The conductivity was measured between stainless steel pistons, at room temperature, by means of an ac bridge (Waynne Kerr Universal Bridge B 224), at fixed frequency of 1.0 kHz. During the measurement, pressure was maintained at the mentioned value. All samples were dried in vacuum at 60 °C for 3 h before the conductivity measurement. The thermogravimetric analysis was carried out using a TA Instruments model SDT 2960 thermoanalytical device in an air stream (35 mL min-1) at a heating rate of 10 °C min-1. Elemental analysis (C, H, N, and S) was performed using an Elemental Analyzer VARIO EL III (Elementar). The content of Al and Si in the composites was determined by inductively coupled plasma (ICP), using a iCAP6500 Duo ICP spectrometer (Thermo Scientific). The sample was placed in a platinum crucible, and the PANI part of the composite was burned using a Bunsen burner. Then, the inorganic residue (zeolite) was fused with sodium carbonate (weight ratio Na2CO3/zeolite ) 16) for 45 min, dissolved in water, and analyzed by ICP. FTIR spectra of the samples were recorded in the range of 400-4000 cm-1 using a MIDAC M 2000 Series Research Laboratory FTIR Spectrometer at 4 cm-1 resolution. Powdered samples were dispersed in KBr and compressed into pellets. UV-visible spectra of the deprotonated samples dissolved in N-methyl-2-pyrrolidone (NMP) were recorded using a UV-vis Spectrometer GBC Cintra 10e. The EPR spectra of solid-state samples were recorded at room temperature using a Varian E104-A EPR spectrometer operating at X-band (9.3 GHz) using the following settings: 1 G modulation amplitude, 100 kHz modulation frequency, 10 mW microwave power, 200 G scan range, and 4 min scan time. Spectra were recorded and analyzed using EW software (Scientific Software). The X-ray powder diffraction (XRPD) patterns were obtained on a Philips PW-1710 automate diffractometer using a Cu tube operated at 40 kV and 35 mA. Diffraction data were collected in the 5-65° 2θ region counting at every 0.02°. Nitrogen adsorption-desorption isotherms were determined on a Sorptomatic 1990 Thermo Finningen at -196 °C. Samples were degassed at 95 °C for 24 h. The specific surface area of samples, SBET, was calculated according to the Brunauer, Emmett, Teller method from the linear part of the nitrogen adsorption isotherms (0.05 < p/p0 < 0.35, where p and p0 are the equilibrium and saturation pressure of N2 at the temperature of adsorption).37,38 Total pore volume was calculated according to the Gurvitch method for p/p0 ) 0.98.37,38 The pore size distribution for mesopores was calculated according to the Dollimore-Heal method from the desorption branch of the isotherm.39 Porosimetry measurements were carried out on a Carlo Erba Porosimeter 2000 using the Milestone 100 Software System. This high-pressure mercury intrusion porosimeter operates in the interval 0.1-200 MPa, enabling estimation of pores in the interval 7.5-15 000 nm. In the porosity measurements, all composite samples were analyzed as pellets because powder samples have large interparticle distances, which would give irrelevant porosimetry data. When pure PANI is pressed into pellets it loses both micro- and mesoporosity; therefore, Hg porosimetry and BET analysis of PANI in pellet form could not be performed. For that reason pure PANI was analyzed as a powder by Hg porosimetry; however, because of small PANI particle size, BET analysis was not operational due to the vacuum required by this method. Aniline adsorption on zeolite HZSM-5 was analyzed using a UV-vis Spectrometer GBC Cintra 10e, at room temperature. HZSM-5 zeolite (200 mg) was dispersed in the aqueous solution (20 mL) of aniline, and the resulting suspension was allowed to equilibrate for 1 h. After centrifugation, aniline concentration was determined by monitoring the decrease in absorbance at the wavelength of absorption maximum of 280 nm.

Results and Discussion The oxidative polymerization of aniline with APS in aqueous zeolite suspensions without added acid is an exothermic process (37) Gregg, S. H.; Sing, K. S. Adsorption, Surface Area and Porosity; Academic Press: New York, 1967. (38) Rouquerol, F.; Rouquerol, J.; Sing, K. Adsorption by Powders and Porous Solids; Academic Press: London, 1999. (39) Dollimore, D.; Heal, G. R. J. Appl. Chem. 1964, 14, 109.

´ iric´-MarjanoVic´ et al. C

Figure 1. Temperature changes during the oxidation of aniline (0.2 M) with APS (0.25 M) in water: without added zeolite HZSM-5 (0) and for the synthesis of PANIZ-1 (b), PANIZ-2 (2), and PANIZ-3 (O) composites. Phases I-IV correspond to the course of aniline polymerization in the presence of zeolite HZSM-5, for the synthesis of PANIZ-1.

(Figure 1). Thermochemistry of these oxidations substantially depends on the zeolite/aniline weight ratio. The synthesis of PANIZ-1 proceeds in two exothermic phases which are well separated by an athermal period (Figure 1), similarly to the corresponding oxidation of aniline in water,10,17 but with lower polymerization rate. This decrease of the rate of aniline oxidation in the presence of zeolite is due to the decrease of the concentration of aniline molecules in the bulk of the aqueous zeolite suspension, because of the partial adsorption of aniline molecules on zeolite HZSM-5. In the first phase at pH > 4, which is accompanied by rapid heat evolution, the fast oxidative oligomerization of aniline with peroxydisulfate occurs (phase I, Figure 1). The acidity of the reaction mixture continuously increases because of the formation of sulfuric acid as a byproduct.10,17 The linear lowmolecular-weight N-C4 coupled aniline oligomers (4-aminodiphenylamine, etc.) as well as branched oligoanilines are formed (Figure 2).17,40-43 The intramolecular oxidative cyclization of low-molecular-weight branched aniline oligomers with peroxydisulfate leads to the formation of substituted phenazines (pseudomauveine, etc., Figure 2).17,40-43 Because the concentration of peroxydisulfate (a strong oxidant) rapidly decreases, the polymerization mechanism becomes based on the redox reactions of nonprotonated nigraniline- [(-C6H4NdC6H4dN-)3n (C6H4NH)2n-] and pernigraniline-like oligoanilines [(-C6H4Nd C6H4dN-)n] (weak oxidants) with aniline and its low-molecularweight protoemeraldine- [(-C6H4NdC6H4dN-)n(C6H4NH)6n-] and leucoemeraldine-like oligomers [-(C6H4NH)n-] (phase II, Figures 1 and 2). During this athermal phase of aniline polymerization, the acidity slowly increases to pH 2.5 and anilinium cation (pKa ) 4.6) becomes prevalent over nonprotonated aniline molecule. The protonation of pernigraniline-like oligoanilines, causing the significant increase of their oxidant power and solubility, coincides with the autoacceleration of aniline polymerization at pH < 2.5 (phase III, Figure 1). In this polymerization phase, sulfate anions (pKa2 of sulfuric acid is ∼2) became also protonated, (40) Círic´-Marjanovic´, G.; Trchova´, M.; Stejskal, J. Collect. Czech. Chem. Commun. 2006, 71, 1407. (41) Círic´-Marjanovic´, G.; Trchova´, M.; Stejskal, J. Int. J. Quantum Chem. 2008, 108, 318. ´ iric´-Marjanovic´, G.; Konyushenko, E. N.; Trchova´, M.; Stejskal, J. Synth. (42) C Met. 2008, 158, 200. ´ iric´-Marjanovic´, G.; Trchova´, M.; Stejskal, J. J. Raman Spectrosc. 2008, (43) C 39, 1375.


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Figure 2. Mechanism of the oxidative polymerization of aniline with APS, in aqueous suspension of zeolite HZSM-5, at zeolite/aniline weight ratio ) 1 (PANIZ-1).

Figure 3. Adsorption isotherm of aniline adsorbed on HZSM-5 zeolite (ceq denotes an equilibrium concentration of aniline in the solution obtained after centrifugation of the aqueous suspension containing aniline and zeolite HZSM-5).

Figure 4. Size of aniline molecule in aqueous medium, determined by the MNDO-PM3/COSMO semiempirical quantum chemical method. The literature value of 0.12 nm for the van der Waals radius of the hydrogen atom was taken into account.

thus promoting the charge separation process in the emeraldine salt form of oligoanilines and PANI, i.e., formation of delocalized polaronic form.41,43 Protonated pernigraniline-like oligoanilines [(-C6H4NH+d C6H4dNH+-)n] react further with remaining anilinium cations and reduced segments of partly oxidized oligoanilines, via the redox equilibrating process, leading thus to the formation of

longer PANI chains in the form of emeraldine salt (PANI hydrogen sulfate) with prevalent N-C4 coupling mode between aniline units (Figure 2). After the temperature reached its maximum, the medium cools down (postpolymerization period, phase IV, Figure 1). The syntheses of PANIZ-2 and PANIZ-3 proceed with slow increase in temperature of the reaction mixture (Figure 1), similarly to the oxidative polymerization of aniline in an acidic

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Figure 5. SEM images of (A) pure PANI, (B, C) PANIZ-1, (D) PANIZ-2, (E) PANIZ-3, and (F) pure zeolite HZSM-5.

aqueous solution at pH < 2,10,42 where much less oxidizable anilinium cations are prevalent over nonprotonated aniline molecules.42 This can be explained by much more efficient adsorption of aniline during syntheses of PANIZ-2 (0.04 M f 0.026 M; 34.4% adsorbed aniline) and PANIZ-3 (0.02 M f 0.008 M; 59.0% adsorbed aniline), compared with the adsorption of aniline during PANIZ-1 synthesis (0.2 M f 0.184 M; 8.1% adsorbed aniline). Since adsorbed aniline molecules are protonated by zeolite

HZSM-5 + C6H5NH2 f (C6H5NH3)+ZSM-5 it follows that ratios ([C6H5NH3+(adsorbed)] + [C6H5NH3+(aq)])/ [C6H5NH2(aq)] at the beginning of PANIZ-2 and PANIZ-3 syntheses are much higher than corresponding initial ratios [C6H5NH3+(aq)]/[C6H5NH2(aq)] in the bulk of aqueous dispersions, indicated by the initial pH of reaction mixtures. It is important to note that, despite the higher local concentration of aniline at

the HZSM-5/water interface, the rate of the polymerization of adsorbed aniline is slowed down because adsorbed aniline molecules are transformed to much less oxidizable anilinium cations. It should also be noted that the zeolite surface changes from hydrophilic to hydrophobic because of the aniline adsorption via the amino group (the hydrophobic benzene ring of aniline remains directed toward the aqueous solution), being thus much less available for the attack of hydrophilic peroxydisulfate anion. The adsorption isotherm of aniline/HZSM-5 zeolite, obtained from UV-visible spectrometry measurements, is shown in Figure 3. The size of the aniline molecule in the most stable conformation in aqueous solution (Figure 4), determined by the MNDO-PM3/ COSMO semiempirical quantum chemical method,8,40-42,44,45 (44) Círic´-Marjanovic´, G.; Blinova, N. V.; Trchova´, M.; Stejskal, J. J. Phys. Chem. B 2007, 111, 2188. (45) Círic´-Marjanovic´, G.; Trchova´, M.; Konyushenko, E. N.; Holler, P.; Stejskal, J. J. Phys. Chem. B 2008, 112, 6976.


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Figure 6. TEM images of (A, B, and C) PANIZ-1 and (D) PANIZ-2.

indicates that the sorption/diffusion of aniline in the HZSM-5 zeolite channel system is a complex process. It is possible only when the aniline molecule is oriented properly (Figure 4) for compression to the size of the HZSM-5 zeolite channels46 [nearcircular (0.54 × 0.56 nm) zigzag channels and elliptical (0.51 × 0.55 nm) straight-chain channels].47Since the compression (conformation change from the most stable to the unstable compressed/twisted conformation) of aniline molecule is an endothermic process, it can be concluded that aniline molecules are adsorbed initially on external surfaces of zeolite. Sub(46) Choudhary, V. R.; Nayak, V. S.; Choudhary, T. V. Ind. Eng. Chem. Res. 1997, 36, 1812. (47) Kokotailo, G. T.; Lowten, S. L.; Olson, D. H.; Meir, W. M. Nature 1978, 272, 437.

sequently, adsorption took place in the zeolite HZSM-5 channel system. SEM and TEM images show the crucial influence of the initial zeolite/aniline weight ratio on the morphology of PANI/zeolite composites (Figures 5 and 6). PANI nanotubes and nanorods are revealed in the nanocomposite PANIZ-1 by SEM (Figures 5B and C) and TEM (Figures 6A-C). PANI nanotubes have an outer diameter of 70-170 nm, an inner diameter of 5-50 nm, and a length extending from 0.4 to 1.0 µm. PANI nanorods have a diameter in the range 60-100 nm and a similar length. It should be noted that the pure PANI, synthesized under similar reaction conditions without added zeolite, contains nanotubes of an average diameter 110-190 nm, Figure 5A. The relative amount of PANI nanotubes and nanorods is significantly reduced in


3128 Langmuir, Vol. 25, No. 5, 2009

Table 2. Elemental Composition of PANI/Zeolite HZSM-5 Composites Determined by the Elemental Analysis (C, H, N, and S), ICP Measurements (Al and Si), and Difference (O)a content (%) sample

C

H

N

S

Al

O (by difference)

Si

PANIZ-1 calcd 24.06 2.73 4.66 5.32 1.21 19.00 found 28.15 2.77 5.76 3.19 1.10 18.75 PANIZ-2 calcd 8.53 1.27 1.66 1.90 2.08 32.52 found 10.09 1.34 2.01 0.93 2.02 33.93 PANIZ-3 calcd 5.06 1.08 0.98 1.12 2.31 36.04 found 6.02 1.19 1.16 0.44 2.29 38.32

43.02 40.28 52.04 49.68 53.41 50.58

a The elemental composition calculated on the basis of the content of PANI hydrogen sulfate, zeolite, and water in PANIZ composites (determined by TGA) is also shown.

Figure 7. TGA curves for PANIZ-1, PANIZ-2, and PANIZ-3 composites, pure PANI, and pure zeolite HZSM-5, recorded in an air stream. Table 1. Content of Zeolite HZSM-5, PANI, and Water in PANI/Zeolite HZSM-5 Composites, Determined by TGA content (%) sample

zeolite HZSM-5

PANI hydrogen sulfate

H2O

PANIZ-1 PANIZ-2 PANIZ-3

45.50 77.90 86.32

46.42 16.52 9.80

8.08 5.58 3.88

the sample PANIZ-2 (Figure 5D) in comparison with PANIZ1. The sample PANIZ-3, prepared with the highest amount of zeolite HZSM-5, consists of PANI/zeolite aggregates of irregular shape and size (Figure 5E) without the presence of PANI nanotubes and nanorods. PANI/zeolite aggregates, distinct from the morphology of unmodified zeolite HZSM-5 (Figure 5F), are also present in the composites PANIZ-1 and PANIZ-2 (Figures 5B-D). The study of prepared composites by electron microscopies indicates that PANIZ-3 composite is homogeneous, while PANIZ-1 and PANIZ-2 are heterogeneous. Heterogeneity is much more pronounced in PANIZ-1, which contains distinct nanodomains (nanophases) of PANI nanotubes. We proposed that the growth of PANI nanotubes and nanorods occurs in the bulk of the aqueous zeolite HZSM-5 suspension. During the early stages of the oxidative polymerization of aniline in water without added acid, at higher pH, nonprotonated lowmolecular-weight oligoanilines are precipitated as hydrophobic crystallites, which do not adhere to the hydrophilic zeolite crystal surfaces. The nonconducting needlelike nanocrystallites, with high content of fully oxidized oligoanilines which show relatively low redox reactivity (substituted phenazines, which have tendency to build columnar aggregates by stacking,8 and nonprotonated pernigraniline-like oligoanilines), become coated with a conducting PANI hydrogen sulfate film during the third polymerization phase at pH e 2. This leads to the formation of PANI hydrogen sulfate nanorods with nonconducting core and conducting walls. PANI nanotubes are formed by the dissolution of the cores of nanorods,8 induced by the protonation of fully oxidized oligoanilines at pH e 2. The mechanism of polymerization of anilinium cations adsorbed at the surface of zeolite HZSM-5 is proposed to be the same as that of aniline in the presence of strong acids.42 This means that some induction period, caused by the much lower oxidizability of anilinium cations in comparison with aniline base,40 is followed by the rapid exothermic polymerization stadium, which leads to the formation of the ordinary conducting thin PANI film at the crystal aluminosilicate surfaces of zeolite. One-dimensional fibrillar PANI growth within the zeolite channel system is also possible.19

Table 3. Conductivity and Color of Pure PANI, Pure Zeolite HZSM-5, and PANI/Zeolite HZSM-5 Composites sample

initial zeolite/aniline weight ratio

color

conductivity (S cm-1)

PANI PANIZ-1 PANIZ-2 PANIZ-3 HZSM-5

1 5 10 -

dark green dark green green light green white

3.8 × 10-2 2.6 × 10-2 2.6 × 10-5 4.8 × 10-9 1.4 × 10-8

The weight ratio of zeolite/PANI in composites was determined by thermogravimetric analysis (TGA), Figure 7. Taking into account that the combustion of PANI in air stream is completed at 640 °C, and the residual weight refers to the content of zeolite in the composite, as well as that the weight loss from 25 to 200 °C corresponds to the release of residual water, the weight ratio zeolite/PANI

wzeolite/PANI )

residual mass at 640 °C (%) residual mass at 200 °C (%) - residual mass at 640 °C (%)

was determined to amount to 0.98, 4.72, and 8.79 for composites PANIZ-1, PANIZ-2, and PANIZ-3, respectively. The weight ratio zeolite/PANI in PANIZ composites corresponds well to the initial zeolite/aniline weight ratio. Based on TGA results, content of zeolite HZSM-5, PANI hydrogen sulfate, and water in composites is determined, Table 1. It should be noted that composites PANIZ-2 and PANIZ-3 adsorb a lesser amount of water than pure zeolite (∼8%), because PANI chains in these composites blocked a part of active surface of zeolite framework for bonding of water molecules. We have also found that the extent of the thermal decomposition of PANI in PANI/zeolite composites (31.5, 24.9, and 20.9 wt % at 400 °C for PANIZ-1, PANIZ-2, and PANIZ-3 composites, respectively) decreases with the increase of zeolite content, and it is lower than the extent of the thermal decomposition of pure PANI (32.8 wt % at 400 °C). Increased thermal stability of PANI in PANI/zeolite composites can be explained by the strong interaction between PANI and zeolite, which restricts thermal motion of PANI chains. The elemental composition of PANIZ composites found by elemental analysis and ICP measurements corresponds well to that calculated on the basis of the content of PANI hydrogen sulfate [C12H11N2SO4]n, zeolite H6(H2O)16(Al6Si90O192), and water in PANIZ composites, determined by TGA (Table 2). It can be seen that the experimentally determined content of sulfur in PANIZ composites is significantly lower than the calculated content of sulfur. This result indicates that the positive charge on the PANI chains in PANIZ composites is not compensated exclusively by hydrogen sulfate counterions, but also is


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Figure 8. FTIR spectra of (a) pure PANI, (b) PANIZ-1, (c) PANIZ-2, (d) PANIZ-3, and (e) pure zeolite HZSM-5 in the wavenumber range (A) 2000-400 cm-1 and (B) 1700-1200 cm-1 (a detail of Figure 8A).

Figure 9. UV-visible spectra of the deprotonated form of (a) pure PANI, (b) PANIZ-1, (c) PANIZ-2, and (d) PANIZ-3 in N-methyl-2pyrrolidone.

compensated with negatively charged zeolite surface to a considerable extent. The use of zeolite/aniline weight ratio 1 leads to the formation of conducting dark green nanocomposite PANIZ-1, with the conductivity of 2.6 × 10-2 S cm-1, Table 3. This conductivity is of the same magnitude as that of pure PANI, prepared under the same conditions in the absence of zeolite, 3.8 × 10-2 S cm-1. The increase of zeolite content is accompanied by the dramatic decrease of conductivity. The semiconducting (3 × 10-5 S cm-1) PANIZ-2 and nonconducting (5 × 10-9 S cm-1) PANIZ-3 composites were produced using zeolite/aniline weight ratios 5 and 10, respectively, Table 3. It is interesting to note that these samples were also green, PANIZ-3 having light green color. This fact, indicating the presence of conducting PANI emeraldine salt in the semiconducting and nonconducting PANI/zeolite composite materials, could be explained by the formation of “islands” of conducting PANI on the zeolite crystal surfaces. Large interisland contact resistance could significantly reduce conductivity of the bulk sample. It is also interesting to note that the conductivity of pure zeolite HZSM-5 was 1 order of magnitude higher than that of the

Figure 10. EPR spectra of solid samples of pure PANI (A), PANIZ-1 (B), PANIZ-2, (C), and PANIZ-3 (D), measured at room temperature.

composite PANIZ-3, all samples being dried in the same manner (at 60 °C, in vacuo) before the conductivity measurement. This fact can be explained by the effect of residual adsorbed water in pure zeolite HZSM-5, which participates in the conduction, assisting the proton mobility.48 The water sorption in the zeolite channel system in the composite PANIZ-3 is significantly reduced because the PANI chains blocked the active Brønsted centers responsible for the ionic conduction. (48) Higazy, A. A.; Kassem, M. E.; Sayed, M. B. J. Phys. Chem. Solids 1992, 53, 549.


3130 Langmuir, Vol. 25, No. 5, 2009

Figure 11. XRPD patterns of parent HZSM-5 zeolite, PANI/zeolite composites, and pure PANI.

FTIR spectra of PANI/zeolite HZSM-5 composites exhibited the characteristic bands of conducting PANI emeraldine salt (Figure 8). The relative intensities of PANI bands decrease with decreasing PANI content. Characteristic bands of PANI emeraldine salt at 1577 [quinonoid (Q) ring stretching], 1493 [benzenoid (B) ring stretching], 1304 (the C-N stretching of secondary aromatic amine), and 1146 cm-1 (the BsNH+)Q stretching),8,17,49,50 are observed in the FTIR spectrum of PANIZ-1 nanocomposite (Figure 8A, B). The bands originating from the zeolite HZSM-5 appeared at 1227 (external tetrahedron linkages-asymmetric stretching), 1097 (internal tetrahedronasymmetric stretching), 546 (double ring), and 455 cm-1 (TsO bending, internal tetrahedron).51,52 The characteristic band of the conducting emeraldine salt form assigned to C-N•+ stretching vibration, observed at 1246 cm-1 in the spectrum of pure PANI, is overlapped with the stronger zeolite band at 1227 cm-1 in the spectrum of the PANIZ-1 nanocomposite.8,49 The band at 804 cm-1 in the spectrum of PANIZ-1 is due to the mixed contribution of the γ(C-H) vibration of 1,4-disubstituted benzene ring in the linear PANI backbone, and the symmetric stretching vibration of external linkages in zeolite, which appear at 810 and 796 cm-1 in spectra of pure PANI17 and zeolite,51,52 respectively. It is important to note that the band at 879 cm-1 [γ(C-H) vibration of 1,2,4-trisubstituted benzene ring],50 indicative of branched PANI chains,17 and/or hydrogen sulfate ions,50 is also present. The characteristic PANI bands are blue-shifted to 1593, 1498, and 1306 cm-1 in the spectrum of PANIZ-2, in comparison with the corresponding bands in the spectrum of PANIZ-1 at 1577, 1493, and 1304 cm-1 and those in the spectrum of pure PANI at 1577, 1483, and 1304 cm-1. These shifts indicate the increased (49) Sapurina, I.; Osadchev, A. Yu.; Volchek, B. Z.; Trchova´, M.; Riede, A.; Stejskal, J. Synth. Met. 2002, 129, 29. (50) Infrared and Raman Characteristic Group Frequencies; Socrates, G., Ed.; Wiley: New York, 2001, pp 94-9, 107, 221. (51) Zeolite Molecular SieVes: Structure, Chemistry, and Use; Breck, D. W., Ed.; Wiley: New York, 1974, pp 414-425, 460-465. (52) Narayanan, S.; Sultana, A.; Le, Q. T.; Auroux, A. Appl. Catal., A 1998, 168, 373.

Table 4. Specific Surface Area (SHg), Specific Pore Volume (Vp), and Pore Diameter (D) of PANI/Zeolite HZSM-5 Composites, Determined by the Mercury Porosimetry Method sample a

PANI PANIZ-1 PANIZ-2 a

SHg/m2 g-1

Vp/cm3 g-1

D/nm

34.6 11.9 0.8

2.2 0.31 0.01

3616 92 115

PANI is analyzed as a powder sample.

Figure 12. Cumulative pore-size distribution curves of PANI/zeolite composites.

interaction of PANI chains with zeolite, with the increase of zeolite content, through electrostatic attraction of positively charged PANI chains with negatively charged aluminosilicate surfaces, hydrogen bonding, and ion-dipole and dipole-dipole interactions. Because PANI nanotubes and nanorods are much less adherent to zeolite crystal surfaces than PANI film, it can be proposed that increased PANI-zeolite interactions are most probably caused by the increased weight ratio PANI film/PANI nanostructures. In the FTIR spectrum of PANIZ-3, the bands of zeolite HZSM-5 are prevalent over the PANI bands. The PANI band due to the B-ring stretching is observed at 1498 cm-1, Figure 8B, but the band due to the Q-ring stretching is masked by the band of water, adsorbed by zeolite, at 1626 cm-1.51 The


Langmuir, Vol. 25, No. 5, 2009 3131

Table 5. Specific Surface Area (SBET), Specific Pore Volume (Vp 0.98), and Pore Diameter (D) of PANI/Zeolite HZSM-5 Composites, Determined by the BET Method sample

SBET/m2 g-1

Vp 0.98/cm3 g-1

D/nm

HZSM-5 PANIZ-2 PANIZ-3

400 125 193

0.16 0.24

3.7 3.8

band corresponding to the bending vibration of water adsorbed by zeolite is red-shifted from 1630 cm-1 in the spectrum of neat zeolite to 1606 (shoulder), 1614 (shoulder), and 1626 cm-1 in the spectra of PANIZ-1, PANIZ-2, and PANIZ-3, respectively, Figure 8A and B. The UV-visible spectra of the deprotonated PANIZ composites and deprotonated pure PANI show two absorption maxima in NMP (Figure 9). The UV-visible spectrum of pure nanotubular PANI base consists of the bands at 339 and 620 nm. The band at 339 nm has been assigned to the π f π* electronic transition, and its position corresponds well to that observed for standard PANI emeraldine base at ∼330-340 nm.53-55 This band is sensitive to the number of aniline units. The band at 620 nm corresponds to the “exciton” band which has been attributed to a charge transfer from the highest occupied energy level, centered on the benzenoid ring, to the lowest unoccupied energy level, centered on the quinonoid ring.53,54 The exciton band can be used as a measure of the oxidation state of PANI, and it is observed at ∼637 nm for the “standard” emeraldine base.53,54 The UVvisible spectra of PANIZ composites exhibit two absorption maxima, which show blue-shifting with the increase of the zeolite content in composites: from 320 and 616 nm for PANIZ-1 to 311 and 591 nm for PANIZ-2, and to 309 and 565 nm for PANIZ-3. It can be concluded that PANI is partly oxidized in all composites, the oxidation state of PANIZ-1 being very close to that of pure nanotubular PANI, i.e., the emeraldine state, in agreement with the blue color of the solutions of PANIZ-1 and pure nanotubular PANI in NMP. Since fully oxidized pernigraniline base has absorption maxima at about 530 and 320 nm,54 the UV-visible spectra of PANIZ-2 and PANIZ-3 indicate that the oxidation state of PANI in these composites is between emeraldine and pernigraniline state, and/or that their chain length is lower in comparison to PANI and PANIZ-1. The EPR spectra confirm the presence of radical cations, characteristic for conducting PANI emeraldine salt (Scheme 1), in all PANIZ samples (Figure 10). The EPR signal of pure PANI and all composites represent a singlet with g ) 2.003. The EPR signals of pure PANI, PANIZ1, and PANIZ-2 have similar shape, while PANIZ-3 shows significantly broader EPR signal. The broadening of the EPR signal can be explained by the reduction of the electron diffusion caused by the presence of zeolite. Similar observation was reported for the PANI/Na+-montmorillonite clay nanocomposite.56 Nanocomposite PANIZ-1 shows a signal of slightly smaller peak area compared to pure PANI. The EPR peak area relative to pure PANI substantially decreases with increasing zeolite content in the order 0.95, 0.19, and 0.09 for the samples PANIZ-1, PANIZ2, and PANIZ-3, respectively. Zeolite HZSM-5 has no EPR signal. X-ray powder diffraction analysis proved that the crystallinity of zeolite HZSM-5 in the composites is the same as that of the original HZSM-5, Figure 11. (53) Kang, E. T.; Neoh, K. G.; Tan, K. L. Prog. Polym. Sci. 1998, 23, 277. (54) Quillard, S.; Louarn, G.; Lefrant, S.; MacDiarmid, A. G. Phys. ReV. B 1994, 50, 12496. (55) Laska, J. J. Mol. Struct. 2004, 701, 13. (56) Kim, B. H.; Jung, J. H.; Joo, J.; Kim, J. W.; Choi, H. J. J. Korean Phys. Soc. 2000, 36, 366.

Figure 13. Nitrogen adsorption-desorption isotherms of the PANI/ zeolite composites.

Mercury intrusion porosimetry measurements (Table 4, Figure 12) indicate that the increase of zeolite content in PANIZ composites leads to lower specific surface area and lower specific pore volume. PANIZ-1 is mesoporous, while PANIZ-2 contains only micropores. Therefore, composites with higher content of zeolite, PANIZ-2 and PANIZ-3, were analyzed using the BET method (Table 5, Figure 13). The nitrogen adsorption-desorption isotherms (Figure 13) have a reversible part at low relative pressures and hysteresis loops at higher relative pressures (H3 type of hysteresis cycle), characteristic for aggregated plane particles which form slit-shaped pores.37,38 The decrease of specific surface area and specific pore volume with the increase of PANI content in PANI/zeolite composites is caused by the blockade of the zeolite HZSM-5 pores with PANI.

Conclusion In summary, we have demonstrated an efficient templatefree method for the synthesis of conducting PANI nanotubes/ zeolite nanocomposite, through the oxidative polymerization of aniline with ammonium peroxydisulfate in aqueous suspension of zeolite HZSM-5 without added acid, by using initial zeolite/aniline weight ratio ) 1. This simple and versatile synthetic method could be extended to prepare a wide range of other nanocomposites of conducting self-assembled PANI nanotubes and various inorganic materials. PANI/zeolite HZSM-5 nanocomposite contains PANI nanotubes, which have a typical outer diameter of 70-170 nm, an inner diameter of 5-50 nm, and a length extending from 0.4 to 1.0 µm, accompanied by PANI nanorods with a diameter of 60-100 nm and PANI/zeolite mesoporous aggregates. PANI nanotubes/zeolite nanocomposite shows similar conductivity (∼ 10-2 S cm-1), oxidation state (emeraldine), and paramagnetic properties (g)2.003), as well as improved thermal stability of the PANI chains in comparison with pure self-assembled PANI nanotubes. This novel composite, which combines unique properties of 1D PANI nanostructures and mesoporous PANI/zeolite hybrid materials, could be applied as an electronic component, sensor, and catalyst. Acknowledgment. The authors wish to thank the Ministry of Science and Technological Development of Serbia (Contracts Nos. 142055 and 142047) and the Grant Agency of the Academy of Sciences of the Czech Republic (IAA 400500405) for the financial support. LA8030396

Synthesis and Characterization of Conducting Self-Assembled

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