Preparation and characterization of polyaniline-containing Na-AlMCM-41 as nanocomposite material with semiconductor properties

OSCAR A. ANUNZIATA; MARCOS B. GÓMEZ COSTA; RODOLFO D. SÁNCHEZ

Cape Town, South Africa

Simposio; International Mesostructured Material Symposium (IMMS 2004); 2004

IMMS

Objectives Mesoporous molecular sieves type MCM-41 with a hexagonal packed array of channels and a narrow pore size distribution [1], offer unique opportunities for the preparation of new nanostructure composite materials. So, the encapsulation of nanosized semiconducting polymer filaments such as polyaniline into the channels of Al-MCM-41 mesoporous hosts, would permit the feasibility of using it as nanometer-scale for electronic devices [2]. First, we study of aniline adsorption into the Al-MCM-41. The host is a strongly hydrophilic material and therefore, the co-adsorption of water should be considered when aniline adsorption on Na-AlMCM-41 is studied due to water molecules would compete with the aniline for active sites of the material. Semiconducting polyaniline (PANI)/MCM-41 composites has been synthesized by an in-situ polymerization technique. Methods Previously of the in-situ polymerization, the adsorption of aniline was studied on Na-Al-MCM-41, synthesized and characterized by us [3]. When the mesostructure containing adsorbed water, the co-adsorption of aniline could occur by weak hydrogen bonding through surface water molecules. Na-AlMCM-41 samples, dehydrated at 200°C and 400°C under vacuum (10-5 Torr.) for 1 hour and non-dehydrated were exposed to equilibrium vapors from liquid aniline at 60°C (6 Torr) for 48hs. The In-situ PANI preparation in the host was carried out as follows: The polyaniline-MCM-41 composite was made using aniline adsorbed on MCM-41, and then polymerized using ammonium peroxydisulfate, after the formation of aniline hydrochloride by the aggregated of HCl at 0 °C and adequate pH. Results Previously of the in-situ polymerization, the adsorption of aniline on Na-AlMCM-41, has been characterized by thermo-infrared spectroscopy, temperature programmed desorption (TPD) and differential thermal analysis methods. Aniline would be mostly bound to mesostructure through weak π interactions. If the mesostructure contains adsorbed water, the co-adsorption of aniline could occur by weak hydrogen bonding through surface water molecules. [4].  The FTIR spectrum of pure PANI, shows band such us Stretching ring (Quinoid) at 1558.6 cm-1 and Benzoid ring deformation at 1479.5 cm-1. The FTIR spectra of the in-situ polimerizated material (PANI-Na-AlMCM-41) shows the characteristic bands of the pure PANI. It show the bands at 1585 cm-1 (Stretching Quinoidal ring), the band at 1498.8 cm-1 belongs to Benzoid ring deformation and the bands attributed at N-H stretching at 3400-3100 cm-1. The bands at 1620-1622 cm-1 characteristic of the NH2 group were not detected, indicating that in our nanocomposite, aniline is not found as free specie [5]. On the other hand, in the composite (PANI-Na-AlMCM-41) interaction could be responsible of not identified peaks. After the polymerization, the composite was filtered and washed with HCl 0.2 M. The solution was studied by Uv-Vis. The Uv-Vis spectrum of PANI with characteristic maxim (λmax) at 425, 575 and 725 nm was found. Magnetization and conductivity studies were performed to the composite (PANI-Na-AlMCM-41). In this way the conductivity of the composite at room temperature was 0.0071  Ώ-1m-1. The material shows a semiconductor properties because its conductivity decreases as the temperature increases. Conclusions Thermo-FTIR spectroscopy showed that aniline is weakly bonded to Na-Al-MCM-41 mesostructure either directly or through adsorbed water molecules. Aniline would be held by p interactions between the aromatic ring and the structural SiOH groups, to completely dehydrated material. Besides, when the samples retain water before aniline was adsorbed, associations between mesostructure, water and organic molecules would be also possible by weak hydrogen bonding. Therefore, the sodium form of Al-containing MCM-41 molecular sieves would be capable to properly retain aniline. The material shows a semiconductor properties because its conductivity decrease with the temperature increment. We suggest that it is possible to obtain the in-situ polymerization of aniline onto the Na-AlMCM-41. In this way, we are continuing this study to optimized the preparation of PANI-MCM41 composite material. References 1.C.Kresge, M.Leonowicz, W.Roth, J.Vartuli, J.Beck, Nature 359(1992)710. 2.K.Moller, T. Bein,  Chem Mater. 10(1998)2950. 3.G. Eimer, L. Pierella, G. Monti, O. Anunziata; Catal.Lett., 78(1-4) (2002)65. 4.G. Eimer, M. Gómez, L. Pierella, O. Anunziata, J.Col.Interf. Scie., 263(2003)400. 5.W.Feng, X.D.Bai, Y.Q. Lian, X.G. Wang, K. Yoshino, Carbon 1(2003)1.