Formation of a Novel Polypyrrole/Porous Phosphate Glass Ceramic Nanocomposite

Note

Formation of a Novel Polypyrrole/Porous Phosphate Glass Ceramic Nanocomposite

Iara F. Gimenez, and Oswaldo L. Alves

Laboratório de Química do Estado Sólido, Instituto de Química, UNICAMP, C.P. 6154, 13083-970 Campinas - SP, Brazil

Este trabalho focaliza a obtenção de um novo nanocompósito, formado mediante a polimerização in situ de monômeros de pirrol na superfície dos poros de vitrocerâmicas porosas com esqueleto LiTi₂(PO₄)₃, após troca-iônica com cobre.

This work is concerned with evidences of a new composite system, formed by in situ polimerization of pyrrole moieties in the copper-exchanged pore surface of LiTi₂(PO₄)₃ glass ceramic.

Keywords: polypyrrole, porous glass-ceramics, nanocomposites

Introduction

Many aspects can justify efforts towards the preparation of conducting polymers within bulk matrices. When the host material has nanometric pores, occurence of cross-linking during the polimerization can be minimized by simple physical constraints, and as a consequence the electrical conductivity can be increased or decreased depending on the type of used matrix¹. For instance, preparation of linear polypyrrole chains inside the pore structure of Porous Vycor Glass has been described by Alves and co-workers^2-4. Alternatively, interest can arise when the porous host exhibits ionic conductive properties, such as the well known Nasicon-type solids⁵. In this context, this work reports the preparation of polypyrrole inside the pores of Nasicon-type LiTi₂(PO₄)₃ glass-ceramics⁶.

Experimental

Original glass samples of nominal composition 6Li₂O.24TiO₂.39CaO.31P₂O₅ were prepared by melting reagent grade Li₂CO₃, CaCO₃, TiO₂ (anatase) and P₂O₅ in platinum crucibles at 1350 °C for 1 h in air. The melts were poured onto carbon plates and annealed at 630 °C for 1 h. Glass-ceramic samples were prepared by the thermal treatment of the glasses at 630 °C for 24 h and subsequently at 720 °C for 12 h. Immersion of glass-ceramic plates in 1 Mol/L HCl aqueous solutions, at room temperature for 24 h, allows the formation of a continuous porous network. Exchange of Li⁺ and H⁺ ions originally present in the pore surfaces by Cu²⁺ ions was performed by immersion of the glass-ceramic plates in 1 Mol/L Cu(CH₃COO)₂ aqueous solutions, at room temperature for 24 h.

Composite preparation was performed by heating the glass-ceramic samples in the excess of freshly distilled pyrrole, at the boiling temperature of the liquid during 1 h. Raman spectra were recorded using a Renishaw Raman Imaging Microscope System 3000, using the 632.8 nm line of a He-Ne laser. Electron Scanning Micrographs were recorded using a MEV JEOL JSM T-300 Microscope.

Results and Discussion

According to TGA measurements, the amount of polymer present in the nanocomposite samples was found to be around 3.5% in weight. Figure 1 shows the photomicrographs of the glass-ceramic samples in (A) and of the nanocomposite samples in (B). The glass-ceramics exhibits fine-grained microstructures, with numerous voids present along the surface. After the growth of polypyrrole, a rough texture covering the ceramic surface can be observed.

The Fig. 2 shows Raman spectra obtained from different points on the surface of the same sample. A typical spectra of the original glass-ceramic can be observed in (D), showing only orthophosphate bands related to the LiTi₂(PO₄)₃ phase ⁵, centered at 1003, 986 and 966 cm^-1. The spectra shown in (B) and (C) both reveal the coexistence of typical polypyrrole and phosphate bands. The spectrum shown in (A), however, is dominated by polypyrrole bands. Concerning the conductive polymeric phase, more than provide evidences of polymerization, the vibrational spectroscopies can be used to get information about the degree of oxidation of conducting polymers⁷. In (A), the bands at 1594 cm^-1 and 1360 cm^-1 can be associated to the presence of polypyrrole in partially dopped states. In the neutral form of polypyrrole, the last band is most likely to occur above 1610 cm^-1. Additionally, the bands observed near 943 cm^-1 and 1048 cm^-1 can be assigned to the structures responsible for charge transport through the chains, namely bipolarons and polarons⁷. Finally, the Raman spectra in Fig. 2 are in good agreement with those reported by Alves and co-workers^2-4, for polypyrrole present in the pores of Porous Vycor Glass.

In summary, preliminary data reported here allows us to conclude that the porous copper (II) exchanged LiTi₂(PO₄)₃ glass-ceramics is a suitable host for obtaining stable nanocomposites through its interaction with polypirrol. Studies related with the electrical conductivity and redox properties are in progress in our laboratory.

Acknowledgments

The authors are gratefull to CNPq, Fapesp and PRONEX-MCT for the financial support.

Received: December 11, 1998

FAPESP helped in meeting the publication costs of this article

e-mail: [e-mail] and [e-mail]

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• 3. Zarbin, A.J.G.; De Paoli, M-A.; Alves, O.L. Synth. Met 1997, 84, 107.
• 4. Zarbin, A.J.G.; De Paoli, M-A.; Alves, O.L. Synth. Met 1999, 99, 227.
• 5. Tarte, P.; Rulmont, A.; Merckaert-Ansay, C. Spectrochim. Acta 1986, 42A, 1009.
• 6. Hosono, H.; Zhang, Z.; Abe,Y. J. Am Ceram. Soc. 1989, 72, 1587.
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Publication Dates

• Publication in this collection
  23 Oct 2002
• Date of issue
  1999

History

• Received
  11 Dec 1998