JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS Vol. 8, No. 5, October 2006, p. 1944 - 1950 Physicochemical features of polyaniline supported heteropolyacids A. POPA, NICOLETA PLEŞU, V. SASCA, E. E. KIŠ a , RADMILA MARINKOVIĆ-NEDUČIN a Institute of Chemistry of Romanian Academy Timişoara, Bl.Mihai Viteazul 24, Romania a University of Novi Sad, Faculty of Technology, Cara Lazara 1, Novi Sad, Serbia and Montenegro Polyaniline with incorporated heteropolyanions was prepared by using a two-step reaction. This method involved synthesis of polyemeraldine base by polymerisation of aniline followed by deprotonation with ammonia. Then polyemeraldine base was protonated with heteropolyacid (HPAs) in a mixture water: ethanol = 1:1. The structure and texture of H 3 PMo 12 O 40 (HPMo) and H 4 PVMo 11 O 40 (HPVMo) supported on polyaniline was studied by XRD, FT-IR, low temperature nitrogen adsorption and scanning electron microscopy (SEM) with EDS analysis. Thermal stability of both HPAs supported on polyaniline was studied by TG and DSC measurements. The thermal decomposition of PANI support started at ca. 400ºC, while for PANI-supported HPAs a decrease of decomposition temperature are observed. FT-IR studies showed that HPAs anions preserved their Keggin structure after deposition on polyaniline support. X-ray diffraction and SEM studies confirmed the uniformity of the distribution of active phase in the catalyst samples. The values of specific surface area of both HPAs increased by deposition on polyaniline support. It is found that most of HPMo and HPVMo (active phases) in samples are well dispersed on the support and polyaniline-supported HPA still keeps its Keggin structure. The surface morphology of the PANI-supported samples is almost similar to that of PANI support. A relatively uniform distribution of active phase in the support pores was evidenced by EDS analysis. (Received May 25, 2006; accepted September 13, 2006) Keywords: Heteropolyacids, Polyaniline, Texture, Structure, Thermal stability, BET, SEM, XRD 1. Introduction Heteropolyacids (HPAs) with Keggin structure have been widely used in acid-catalysed reactions as well as oxidation reactions both in the heterogeneous and homogeneous systems [1-5]. Pure HPAs generally show low catalytic reactivity owing to their small surface area. In order to be more effective for catalytic reactions, HPAs are usually impregnated on different porous materials [6- 14] and polymers [15-20]. Polymer materials have been widely used in chemical reactions as supports or catalysts due to their flexible applicability [15-22]. Polyaniline (PANI) is a conductive polymer, is cheap and stable to heat and air atmosphere. It is also the first commercially available conducting polymer. PANI refers to a class of polymers, which the polymeric chain consists of a succession of reduced benzenic nucleus and oxidised quinoidic nucleus. The synthesis and the characterisation of PANI doped with different anions are critical since many properties of the final polymer are greatly influenced by the nature of the doping ion, properties that provide the special destination of it. The first attempt of the electrocatalytic application of PANI was mentioned by Keita et al [27] and Bidan et al [28] by incorporation of Keggin type heteropolyanions into PANI. M.Hasik et al [15, 16] show that PANI base can be used as convenient catalytic support on which non-oxidising heteropolyanions can be dispersed via protonation. This protonation reaction results in the formation of an ionic bond between heteropolyanions and the support and should also modify the acid-base properties of the catalyst. HPAs catalysts immobilized on conjugated conducting polymers have found successful applications as heterogeneous catalysts in some vapor-phase reactions such as ethanol and 2-propanol conversion [15-17, 19]. The type of carrier, textural and structural properties influence the thermal stability and the catalytic activity of Keggin-type heteropolyacids. In order to obtain highly dispersed heteropolyacids species, H 3 PMo 12 O 40 and H 4 PVMo 11 O 40 were supported on polyaniline (PANI). The goal of this work was to characterise the texture and structure of these heteropolyacids supported on polyaniline in reference to the bulk solid heteropolyacids. 2. Experimental H 4 [PMo 11 VO 40 ]·12H 2 O was prepared by two methods: Tsigdinos and hydrothermal method [29-30]. In both cases HPAs were crystallized slowly from aqueous solutions at room temperature. H 3 [PMo 12 O 40 ]·13H 2 O was purchased from Merck. The as-received material was recrystallized prior to use. They are stable at room temperature with 12-14 H 2 O molecules. Polyaniline (PANI) with incorporated heteropolyanions was prepared by using a two-step reaction. This method involved syntesis of polyemeraldine base by polymerization of aniline with (NH 4 ) 2 S 2 O 8 in HCl followed by deprotonation with ammonia [15-18]. The HPA active phase deposition on the PANI support was performed by protonation from water : ethanol = 1:1 solution. The HPMo and HPVMo acids were deposited by protonation in the concentration of 16.6 wt. % loading.