SYNTHESIS OF 1-D AND 3-D NANOSTRUCTURED POLYPYRROLE VIA DIFFERENT AZO DYES

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1 YTHEI F 1-D AD 3-D ATRUCTURED PLYPYRRLE VIA DIFFERET AZ DYE Jitka KDVA a, Dusan KPECKY a, Přemysl FITL a, Martin VRŇATA a a Department of Physics and Measurements, Institute of Chemical Technology, Prague, Technicka 5, Prague, Czech Republic, skodovaj@vscht.cz Abstract The contribution deals with synthesis and characterization of 1-D and 3-D nanostructured conductive polymer polypyrrole (PPY). anostructured PPY was synthesized by chemical polymerization using soft template method. It is relatively simple and effective preparation of one-dimensional and newly, presented here, three-dimensional structures. This method uses complex of azo dye oxidant as soft template on its surface monomer polymerizes and creates final structures. The complex azo dye - oxidant gradually degrades during polymerization. In the experimental part of presenting contribution Methyl range, Methyl Red, Congo Red, Acid RED 1, range G, unset Yellow FCF, and Tropaeolin odium alt were used as azo dyes. Azo dyes are compounds which have azo group =- and next to azo group there are aromatic nuclei (benzene, naphthalene). The main difference lies mainly in the number of ligands, type and method of distribution of ligands on these aromatic nuclei. The aim of this work was investigate the ability of chosen azo dyes to create complex suitable for the preparation of nanostructures. Morphology of prepared nanostructured PPY was observed by scanning electron microscope (EM). Based on this measurement it was established geometric dimensions of prepared structures. Additionally, for the first time it was obtained the images of tree-dimensional uniform PPY nanostructures, which have not been observed for conductive polymers yet. It was also verified the basic structure of building PPY chains from the spectra obtained by infrared spectroscopy ATR-FTIR. Keywords: polypyrrole, 1-D nanostructure, 3-D nanostructure, soft template, azo dye 1. ITRDUCTI Conducting polymers (CPs) have gained wide attentions since their rediscovery in the 1970s. CPs are very popular for their unique properties. The most important feature is electrical conductivity that can achieve value up to 10 5 cm -1 (electrical conductivity of oriented polymer films or fibres). It was discovered that conducting polymers have the ability to change their conductivity in response to the surrounding environment. Therefore they are called smart polymers 1. Due to these properties there are many possible promising applications, such as: material for biosensors 2 and gas sensors 3, supercapacitors 4, anti-static envelope 5. Recent research dealing with conductive polymers has found that under certain conditions the conducting polymers are able to create uniform structured shapes with nanometric sizes (nanostructures), for example nanotubes, nanowires, nanorods. These shapes are often collectively called 1-D structures of conducting polymers. The description is based on a widely used simplification which assumes that structural properties of 1-D polymer structure are predominantly determined by its longest dimension (which is always orders of magnitude larger than the other two). However, using certain conditions it is possible to synthesize 3-D conducting polymer structures. 1.1 oft template method 1-D structured polymer can be synthesis using template or special template free procedure. There are two means of template synthesis, so-called hard and soft template method. The hard template method uses zeolites and membranes as a hard template. After synthesis, it is necessary to remove hard template. During removal the hard template 1-D structure is damaged and so hard template stays in the solution.

2 Using soft template method for synthesizing polymer nanostructure brings many advantages: (i) change in temperature synthesis, time synthesis or molar ration of reactants can influence the geometric dimension of the prepared 1-D structures, (ii) it is effective, cheap and simple method, (iii) template autonomously degrades after the reaction is over can therefore be easily removed from solution without damaging prepared polymer nanostructure 6. Here presented and used soft template method is based on reaction of azo-dye and oxidant. These components create fibrous structure, so-called soft template. After addition of the monomer, 1-D structure of the polymer form on the surface of the fibres that gradually degrade during reaction (therefore this method is sometimes called self-degradation method). After polymerization, remaining degraded soft template must be removed from 1-D polymer structures by long-washing 6. The molecular structure of azo dyes significantly affects the structure of prepared structured polymer. Therefore it must be reflect strength, number and distance of ligands in a molecule of azo dye, acidobasic properties, degree of molecule planarity, etc. 2. EXPERIMETAL Pyrrole, ferric chloride (FeCl 3 ), Methyl range, Methyl Red, Congo Red, Acid RED 1, range G, unset Yellow FCF and Tropaeolin odium alt were purchased from igma-aldrich and were used without any modifications. The molecular structures of azo dyes are shown in Fig. 1. The synthesis process of the structured PPY was as follows: in 10 mm ferric chloride (oxidant) was dissolved in 200 ml of 5 mm solution of azo dye and deionized water. Molar ration of reactive monomer : oxidant : azo dye was 10:10:1 for all synthesis. Then 700 l pyrrole monomer was added dropwise in the first two hours of synthesis to the solution. The solution was tempered at 5 C and it was stirring during all synthesis of a constant speed. Due to complex structures of prepared PPY restraining the remnants of the template (azo dye) was necessary to use long-washing. Therefore oxhlet extraction was used. The prepared PPY was extracted with ethanol until extraction reagent was colorless (up to one week). The prepared structured PPY was dried at 45 C in vacuum drier. For comparison it was synthesized unstructured PPY. Molar ration of reactants was 1 mm pyrrole : 1 mm FeCl 3 in aqueous environment. The structures of prepared PPY were observed by canning Electron Microscope (EM) JEL model JM- 7500F. Composition of prepared PPY was obtained by Total Reflection Fourier Transform Infrared (ATR- FTIR).

3 a) b) - a + H 3 C CH 3 H 3 C H CH 3 c) H 2 H 2 d) - a + - a + - a + e) a + - H H H 3 C H - a + a + - f) - a + g) - a + H H H - a + Fig 1 Molecular structure of azo dyes: a) Methyl range, b) Methyl Red, c) Congo Red, d) Acid RED 1, e) range G, f) unset Yellow FCF, g) Tropaeolin odium alt 3. REULT AD DICUI Fig. 2a) shows EM image of unstructured PPY which was synthesized by standard chemical polymerization. As seen unstructured PPY has characteristic fruticose formations that create highly disordered arrangement.

4 Fig. 2 tructures of PPY prepared by: a) without azo dye, b) Methyl range, c) Methyl Red, d) Congo Red, e) Acid RED 1, f) range G, g) unset Yellow FCF, h) Tropaeolin odium alt

5 Fig. 2b-h) show EM images of structured PPY prepared by the soft template method using different azo dyes. It is apparent that azo dyes significantly affect the structure of prepared PPY. oft template capability of azo dyes is evident for Methyl Red and Aced RED 1. These azo dyes contribute to the formation of 1-D polymer structure. Dimension of PPY nanotubes prepared from Methyl Red are approximately 80 nm diameter and hundreds of nm length. Dimension of PPY nanotubes prepared from acid RED 1 are approximately 340 nm diameter and units of m length. Azo dyes Methyl Red, range G and Tropaeolin odium alt don t have the ability to polymerization. They cannot connect unites of azo dyes molecules and cannot create a sufficiently large oligomeric structures that would create usable template for synthesis. tructures of prepared PPY are very similar to the PPY prepared without using azo dye. There are characteristic fruticose formations. Further azo dye without ability to polymerization is Congo Red. tructures of this prepared PPY resemble crushed stone. Very interesting formations create PPY synthesized in presence of unset Yellow FCF. There are symmetrical 3-D structures. Probably, the unset Yellow FCF molecule allows creating more spatiallyoriented complex due to insignificant the existence of hydrophilic and hydrophobic parts presence its functional group. ther azo dyes, mention here, have in their structure more hydrophilic and hydrophobic parts which can affect the resulting structure of PPY. Fig 3 verview of ATR-FTIR spectra of PPY prepared in the presence of: a) Methyl range, b) Methyl Red, c) Congo Red, d) Acid Red 1, e) range G, f) unset Yellow FCF, g) Tropaeolin odium alt The main task of ATR-FTIR measurements was to verify the chemical structure of prepared PPY and to detect potential residue of azo dye using during synthesis. Interpretation of the spectra was focused on the region cm -1. Interpretation of PPY spectra is difficult because of variable degree of conjugation of PPY skeleton and a large number of different types of disturbances (non-linear shape of the polymer chain, oxidation by air oxygen, etc.). But in all cases it was found that PPY was prepared (Fig. 3). The unstructured PPY spectrum contains following characteristic peaks: 1527 cm -1 (C-C, C=C stretching), 1427 cm -1 (C=C, C- stretching), 1270 cm -1 (C-H, C- in plane deformation), 1129 cm -1 (breathing vibration of the PY ring), 1086 (C-H, -H in plane deformation), 997 (C-H in plane deformation), 956 (C-C out of plane deformation),

6 849 and 727 (C-H, -H out of plane deformation), 646 (C-C out of plane deformation). These peaks are evident in presented spectra of structured PPY. light shifts in spectra cannot be attributed to direct chemical reaction of pyrrole and azo dye, but only to changes in degree of conjugation of polypyrrole chains. It is apparent that used azo dye is only supporting structure for forming polymer and after polymerization it selfdegradation. 4. CCLUI This contribution deals with preparation of PPY by chemical synthesis in presence of azo dyes. oft template method was used. This method uses azo dye and oxidant as soft template. even different azo dyes were used for synthesis of PPY. Using Methyl range and Acid RED 1 as azo dye PPY nanotubes was prepared. Using Methyl Red, range G and Tropaeolin odium alt as azo dye fruticose formation of PPY was prepared. These shapes resemble unstructured PPY prepared without azo dye. Therefore it can be assumed that these azo dyes are not able to form soft template. Using Congo Red as azo dye PPY resemble crushed stone was prepared. However, the most important shape of PPY was prepared using unset Yellow FCF. There are symmetrical 3-D structures. ATR-FTIR measurements confirmed that in all cases PPY was prepared. ACKWLEDGEMET LITERATURE This work was financial supported from specific university research MMT no. 21/2011, project MMT and Grant Agency of the Czech Republic (GACR) project o. P108/11/1298. [1.] TEJKAL, J. Polyaniline: Vodivé polymery, Cited: , [2.] KUMAR, A. et al. mart polymers: Physical forms and bioenrineering applications. Prog. Polym. ci., 2007, volume 32, page1205. [3.] KPECKÝ, D. Polypyrrole thin films for gas sensors prepared by Matrix-Assisted Pulsed Laser Evaporation technology: Effect deposition parameters on material properties. The olid Films, 2009, volume 517, page [4.] MATRAGTI, M. Polymer-based supercapacitors. Journal of Power ources, 2001, volume 97-98, page 812. [5.] HTAI, A. et al. ynthesis and properties of high-molecular-weight soluble polyaniline and its application to the 4 MB-capacity barium ferrite floppy disk s antistatic coating. ynthetic Metals, 1993, volume 55-57, page [6.] YAG, X. et al. Facile Fabrication of Functional Polypyrrole anotubes via a Reactive elf-degraded Template. Macromolerular Rapid Communications, 2005, volume 26, pages