Evaluation of the doping process of polyaniline produced inside the mesopores of a sulfonic acid grafted MCM-41
Graphical abstract
Highlights
► Aniline polymerization into the pores of a sulfonic acid-grafted MCM-41. ► PAni produced in the emeraldine salt form through a direct auto-doping process. ► Aniline polymerization into MCM-41 template without acid addition. ► Inorganic porous framework acting as template and counter-ion to the doped PAni.
Introduction
The development of nanostructured hybrid materials is a field of intense scientific and technological research due to the unique and enhanced properties that this kind of assembly might presents in respect to its isolated constituents [1]. Hybrid materials containing conducting polymers as organic constituents have been attracting attention due to its potential application to the development of electronic nanodevices and sensors [2], [3].
Inorganic solids with uniform porous architecture in the nanoscopic range are considered good hosts for conducting polymer encapsulation since the empty channels can act as a template for the polymer formation, providing size and morphological control, resulting in polymeric chains with good linearity and less defects, characteristics that are important to enhance the electrical conductivity. In this sense, it is important to mention that there are some studies already published comprising inorganic hosts with different pore dimensionalities and conducting polymers such as polyaniline (PAni) and polypyrrole, that have already been produced inside the one-dimensional pores of MCM-41 [4], [5] and SBA-15 [6], two-dimensional interlayer region of layered niobates [7], clays [8] and FeOCl [9] and into the tri-dimensional interconnected pores of KIT-6 silica [10].
It is worth to note that the electrical conductivity of the most of these hybrid materials is always low due to the presence of the inorganic insulating framework and to the existence of non-interconnected pores, which hamper their application as conductive materials. On the other hand the further inorganic matrix removal is a useful strategy to obtain conducting polymers nanowires that can have technological relevance as components for nanoelectronics [11].
Studies involving the preparation and characterization of hybrid materials containing PAni, one of the most studied conducting polymer, and MCM-41 have already been published [4], [5], [12], [13], [14], [15] and although the reported low electrical conductivity values of these materials (around 10−9 S cm−1) [12], [13], they are attractive materials due to their good photocatalytic activity under visible light and to the electrorheological (ER) properties as dispersed phase in fluids [12].
Taking into account such aspects the main goal of this work is to obtain a hybrid material containing PAni inside the pores of a sulfonic acid grafted MCM-41 silica. The presence of the –SO3H groups covalently bounded to the surfaces of the silica pores might be able to promote the polymer self doping during the in situ preparation does not requiring the use of a strong mineral acid during the polymerization step, which is the necessary medium in most of the synthetic procedures already published [4], [5], [12], [13], [14], [15]. In addition, the electrostatic interaction established between the terminal groups and the positive charged PAni, due to the protonation, can be an important feature to afford improved properties to this hybrid material to be used in the as previously cited applications [12].
Section snippets
MCM-41 synthesis
It is already published in the literature many procedures for the MCM-41 synthesis using different types of inorganic precursors, structure-directing agents and reactants molar ratios and much of these procedures were recently reviewed [16]. In the present study it was selected a method that produces well ordered silica mesophase using small quantity of template [17]. This method consists in the controlled hydrolysis of tetraethylortosilicate (TEOS, Aldrich), under basic condition (NaOH,
Results and discussion
The XRD pattern of the synthesized MCM-41 (Fig. 1a) indicates that the mesoporous material was obtained with structural order and pores regularity due to the presence of many orders diffraction peaks, that is an indication of the parallel arrangement of the cylindrical pores of MCM-41 [19]. The calculated d100 interplanar distance of 34.4 Å is consistent with the expected value for the mesophase obtained by using CTAB as template [20].
The regular pore ordering of the synthesized MCM-41 can be
Conclusions
PAni was successfully produced inside the pores of sulfonic acid grafted MCM-41 silica. The acid group was capable of protonate PAni in an auto-doping process. According to the results PAni was obtained in the emeraldine salt form, the most conductive one, without the requirement of another acid source. The grafted sulfonic acid groups also promoted a stronger interaction between functionalized inorganic framework and the adsorbed aniline than the observed in MCM-41, and the established
Acknowledgments
The authors acknowledge the Brazilian agencies FAPESP and CNPq for the financial support and are thankful to Prof. Vera R.L. Constantino (IQ-USP) for the XRD, TGA and FTIR experiments, to LME/LNNano/CNPEM for the technical support during the HR-TEM work and to the Centro de Microscopia Eletrônica do Instituto Butantan for the TEM analysis.
References (29)
- et al.
Mater. Sci. Eng., B
(2006) - et al.
J. Colloid Interface Sci.
(2010) - et al.
Synth. Met.
(2003)et al.Langmuir
(2004)et al.Composites Sci. Tech.
(2009) - et al.
J. Appl. Polym. Sci.
(2006) - et al.
Mater. Chem. Physics
(2007) - et al.
J. Mater. Chem.
(2007) - et al.
Microp. Mater.
(1995) - et al.
Faraday Trans.
(1996) - et al.
J. Mater. Chem.
(2005) - et al.
Adv. Mater.
(2009)
Science
J. Phys. Chem. B
Macromol. Rapid Commun.
Adv. Funct. Mater.
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