Elsevier

Microporous and Mesoporous Materials

Volume 159, 1 September 2012, Pages 24-29
Microporous and Mesoporous Materials

Evaluation of the doping process of polyaniline produced inside the mesopores of a sulfonic acid grafted MCM-41

https://doi.org/10.1016/j.micromeso.2012.04.006Get rights and content

Abstract

The use of mesoporous materials as hosts for polymers production in a confined environment is a field of great interest, especially in the case of conducting polymers. This method provides size and morphological control in nanoscopic scale and permits the formation of polymeric chains with good linearity and fewer defects, characteristics that could promote enhanced electrical conductivity.

In this study it was evaluated some aspects of the polymerization of aniline inside the pores of the MCM-41 silica post-modified with sulfonic acid groups (–SO3H) covalently bonded to the surfaces. The produced hybrid material containing polyaniline (PAni) into the pores was characterized by X-ray diffractometry, thermogravimetric analysis, UV–Vis electronic absorption, Fourier transformed infrared spectroscopies and scanning and transmission electron microscopies.

The results indicate that PAni was successfully generated inside the pores of the sulfonic acid grafted MCM-41 and that the acid group was capable of protonating the polymer, producing PAni in the emeraldine salt state, the most conductive one, without the addition of another acid source during the polymerization step. The grafted sulfonic acid groups also promoted a stronger interaction between inorganic matrix and aniline than the observed in non-functionalized MCM-41, which resulted in less monomer and polymer lixiviation during the polymerization step.

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 SO3- 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)

  • D. Zhang et al.

    Mater. Sci. Eng., B

    (2006)
  • Y.Q. Dou et al.

    J. Colloid Interface Sci.

    (2010)
  • H.J. Choi et al.

    Synth. Met.

    (2003)
    H.J. Choi et al.

    Langmuir

    (2004)
    F.F. Fang et al.

    Composites Sci. Tech.

    (2009)
  • X. Feng et al.

    J. Appl. Polym. Sci.

    (2006)
  • E.F. Loyola et al.

    Mater. Chem. Physics

    (2007)
  • K. Möller et al.

    J. Mater. Chem.

    (2007)
  • C. Y Chen et al.

    Microp. Mater.

    (1995)
  • A. Jentys et al.

    Faraday Trans.

    (1996)
  • C. Sanchez et al.

    J. Mater. Chem.

    (2005)
  • H.D. Tran et al.

    Adv. Mater.

    (2009)
  • C.G. Wu et al.

    Science

    (1994)
  • C.M.S. Izumi et al.

    J. Phys. Chem. B

    (2005)
  • M.S. Cho et al.

    Macromol. Rapid Commun.

    (2002)
  • G. Yang et al.

    Adv. Funct. Mater.

    (2007)
  • Cited by (18)

    • Lightweight PPy aerogel adopted with Co and SiO<inf>2</inf> nanoparticles for enhanced electromagnetic wave absorption

      2022, Journal of Materials Science and Technology
      Citation Excerpt :

      The absorption peaks at 792.12 cm−1 and 1049.00 cm−1 are associated to the out-of-plane deformation bending and deformation vibration absorption of the CH bond. The 672.40 cm−1 peak is due to the bending vibration of the CH single bond in the PPy heterocyclic plane [34-36]. For SiO2(10%)/PPy sample, there are some difference on the infrared spectra.

    • Tailor-made core/shell/shell-like Fe<inf>3</inf>O<inf>4</inf>@SiO<inf>2</inf>@PPy composites with prominent microwave absorption performance

      2019, Journal of Alloys and Compounds
      Citation Excerpt :

      For Fe3O4, the characteristic absorption peaks at 633 and 582 cm−1 indexed to the FeO bond could be observed [42,43]. Compared to Fe3O4@SiO2, the absorption bands at 460 cm−1, 804 cm−1, and 952 cm−1 are attributed to Si–O–Si rocking vibration, Si–O–Si bending vibration and Si–O stretching vibration, respectively [44]. With the introduction of PPy, the two peaks of FeO become one due to strong interference between SiO2 shell and PPy shell.

    • Snap-top nanocontainer for selective recovery of nickel ions from seawater

      2017, Microporous and Mesoporous Materials
      Citation Excerpt :

      The absence of intense peaks in between 63 and 70 ppm supports the complete removal of the surfactant by solvent extraction and indicates the successful formation of the propyl aniline modified nanocontainer. Fig. 5B represents the TGA profile of PA-MCM-41, which showed a weight loss of 2% bellow 100 °C due to the loss of physisorbed water molecules [54]. The gradual degradation rate was observed at temperatures between 100 and 450 °C were assigned to the removal of organic moiety attached to the MCM-41.

    • Evaluation of the influence of sulfur-based functional groups on the embedding of silver nanoparticles into the pores of MCM-41

      2016, Journal of Solid State Chemistry
      Citation Excerpt :

      The first paper describing the embedding of a noble metal into OMS pores was published in 1996 with the aim of increasing the contrast of mesopores to facilitate the imaging during TEM analysis [8]. However noble metal nanoparticles are especially interesting to be immobilized into OMS due to their intrinsic optical and chemical properties that can lead to the development of enhanced heterogeneous catalysts [9] and sensors [10]. Among the noble metals, silver nanoparticles are especially interesting, due to their surface plasmon resonance [4], catalytic and photocatalytic activities [11] and antibacterial properties [12].

    View all citing articles on Scopus
    View full text