Nickel-Nanoclusters-Containing Polyaniline Composites Having Structure Layer-by-Layer: Part I - the Development of Concept and Structural Morphology

Journal of Chemistry, Vol. 42 (2), P. 236 - 240, 2004<br /> <br /> <br /> <br /> Nickel-Nanoclusters-Containing Polyaniline<br /> Composites Having Structure Layer-by-Layer<br /> Part I - the Development of Concept and Structural<br /> Morphology<br /> Received 17-4-2003<br /> Tran Trung, Tran Huu Trung<br /> Department of Electrochemical Technology and Metal Protection,<br /> Faculty of Chemical Technology, Hanoi University of Technology<br /> <br /> <br /> Abstract<br /> The development of concept in structural morphology lets description the location of<br /> nickel nanoclusters in conductive organic polymers, which may be a new kind of structure in<br /> conductive organic polymer composites family. As a new route, such the development was<br /> supported by electrochemical two-pot process, on which polianiline containing nanoclusters<br /> of nickel incorporated in layer by layer were prepared, in H2SO4 0.1 M solutions. The<br /> presence of nickel nanoclusters in polymer matrix and the changes in morphology were<br /> confirmed by SEM/EDS.<br /> <br /> <br /> I – Develo`pment of concept [1 - 3], or by incorporation of immobilized organic<br /> anions [4 - 6].<br /> Electropolymerization, an interesting method,<br /> On the other way, very small size particles,<br /> has been widely used to prepare conjugated<br /> in micron or submicron scale, of transition metal<br /> polymers, such as polypyrrole, polythiophen,<br /> oxides including MnO2, LiMn2O4, WO3, RuO2<br /> polyaniline [1 - 3]. Such all conjugated polymers<br /> etc. and inorganic polyanions used as dopants for<br /> with spatially extended -bonding system found doping conjugated polymers [1, 7 - 10]. In some<br /> exhibit unique physical and electrochemical cases, microparticles and submicro-particles<br /> properties unobtainable for conventional such as MnO2 and LiMn2O4 can be oxidized<br /> polymers. And it is very well known that during electrosynthesis, and manganese atoms in<br /> depending on the potential value at the end of low oxidative states will transform into high<br /> the electrosynthesis, the polymers have been in oxidative state Mn+6. In consequences, a strongly<br /> various the oxidative states, therefore leading to hybrid between d-unfilled orbitals of manganese<br /> the different physical and electrochemical atom and -electron of polymer chains or/and<br /> properties. lone-pair electrons of nitrogen was formed [1]. It<br /> To improve physical and electrochemical is unobtainable and quite different from<br /> properties, conjugated polymers have been chemically way used to prepare such organic<br /> modified by incorporation of small size ions, Cl-, conductive polymer composites. Metal nanopar-<br /> Br-, BF4-, NO3-, ClO4-, SO22- etc. that can be ticles, such as Pt and Pd nanoparticles [11, 12],<br /> diffusion into and diffusion out polymer matrix and metal complexes [13] have been already<br /> <br /> 236<br /> electrochemically incorporated into polyaniline (PANI).<br /> <br /> PANI Films<br /> A B<br /> <br /> <br /> <br /> PANI layer Nickel-enriched PANI layer<br /> <br /> Aspects of the interconnection of metal nanoclusters and polymer fibrils<br /> Nanoclusters of nickel Polymer fibrils<br /> <br /> <br /> <br /> <br /> Figure 1: Schematic representation of the layer-by layer structured polymer composite film (A)<br /> and polymer composite film in which particles dispersed in to the whole of the<br /> polymer matrix (B), and of several aspects of the interconnection of metal<br /> nanoclusters and polymer fibrils<br /> In all cases mentioned above such dopants This study attempt to find a route, by using<br /> were electrochemically homogeneously disper- electrochemical approach, on which we can<br /> sed into the whole of conjugated polymer film overcome such problems and can control the<br /> (Fig. 1b). In this work, a new concept in distribution of particulates in the whole of<br /> structural morphology, the metal-nanoclusters- polymer matrix or in an alternatively layer<br /> containing conductive organic polymers having structured polymer film, as shown in figure 1. In<br /> structure layer-by-layer was suggested and such composites there exist several aspects of<br /> developed. The success of preparation of nickel- interconnect of nanoclusters of metal and<br /> nanoclusters-containing polyaniline is obviously polymer fibrils (Fig. 1c).<br /> evidence to support the development. The<br /> location of nickel nanocluster, as bridging II - Experimental<br /> nanocluster between polymers fibrils, in polymer<br /> matrix was also suggested (Fig. 2). Another Polyaniline composites containing nanoclus-<br /> striking point in such the preparation is that ters of nickel were electrochemically prepared<br /> different from the electrochemically dispersion by two-pot process and structured layer-by-layer.<br /> of Pd and Pt microparticles into PANI film, the The controlled electropolymerization system for<br /> dispersion of nanoclusters of metals, for preparation of aniline or the controlled electro-<br /> example nickel and iron (their standard redox deposition system for incorporating nanoclusters<br /> potentials are very negative vs. Ag/AgCl of nickel into PANI film were composed of a<br /> electrode), into organic conductive polymers has potentiostat, the EG&E Priceton Applied<br /> met a problem. It is due to the big difference Research model 362 with program Ecuniv-HH5,<br /> between the redox potential of such a metal connected with a standard three electrodes cell<br /> and the potentials, usually ranging from 0.2 V to containing an aqueous solution of 0.1 M aniline<br /> 1.2 V vs. Ag/AgCl electrode, used to electro- monomer or of 0.5 M nickel sulfate, respectively.<br /> polymerize of aniline, pyrrole and thiophen The potential applied on the PANI composite<br /> monomers by potential sweep. Oppositely, the films, which was electrodeposited onto platinum<br /> electro-deposition of metal ions conducted at electrode (S = 1 cm2), was vs. Ag/AgCl reference<br /> potentials very negative to Ag/AgCl electrode. electrode for all electrochemical measurements<br /> <br /> 237<br /> and a platinum sheet was serving as auxiliary The presence of nickel in the obtained PANI<br /> electrode. composite films was confirmed by energy<br /> All chemicals used are in AR grade and dispersion X-ray spectroscopy (EDXS, the<br /> supplied by Merck. To deoxygenate doubly incident angle kept constantly at 35o) equipped<br /> distilled water, for preparation of solutions, and with a scanning electron microscope (SEM)<br /> the electrolyte solution, nitrogen gas was model JEOL JSM-5410LV, which was used to<br /> bubbled before and during experiments. investigate the surface morphology of the films.<br /> <br /> <br /> <br /> <br /> Figure 2: Schematic representation of the structures involving in the generation of principle<br /> forms and charge carriers of PANI as well as of illustration of the role of<br /> nanoclusters of nickel<br /> <br /> III - Structural morphology of form commonly called leucoemeraldine, the<br /> nickel nanoclusters containing fully oxidized form termed pernigraniline, and<br /> the half-oxidized form, emeraldine. The<br /> polyaniline<br /> oxidation state of a PANI film onto the working<br /> As the known well, the PANI film electro- electrode immersed in aqueous acidified solution<br /> oxidized during potential sweep in voltammetry depends on the applied potential and the<br /> can be existed in a variety of form, which differs presence of dopants (Fig. 3). The presence of<br /> in their oxidative level. Principle neutral forms nickel nanoclusters incorporated into PANI<br /> of PANI were consisting of the most reduced matrix leads to the changes in the density of<br /> <br /> 238<br /> charge carriers, consequently leading the shift of during electropolymerization of aniline, the<br /> anodic waves of cyclic voltammetry, as shown in branched PANI chains were performed and<br /> figure 3. Like cyclic voltammograms in aqueous twisted together to form the branched PANI<br /> acidified solution, the cyclic voltammograms of fibrils as observed by SEM studies (Fig. 4). As<br /> PANI film conducted in 0.1 M H2SO4 solution, at seen there is quite difference in structural surface<br /> potential scanning rate of 50 mV.s-1 consists of morphology between PANI film and PANI film<br /> two main peaks of oxidation (Fig. 3d). The first containing nanoclusters of nickel (PANI-Ni).<br /> one maximum at 0.2 V vs. Ag/AgCl reference PANI-Ni film seems just structured of a number<br /> electrode corresponds to the oxidization of leuco- of the coral-like branched polymer matrix<br /> emeraldine to emeraldine, and the second one consisting of twisted polymer fibrils. Meanwhile,<br /> maximum at a higher potential of 0.7 V attribu- PANI film shows its structural surface<br /> ted to the oxidization of emeraldine to pernigra- morphology like a “fishing-net” with unit cells<br /> niline. Except for just mentioned there also exist covered by slab of PANI. Especially, the PANI<br /> an obtuse peak (a shoulder) in the middle. The polymers in coil shape, present in PANI film,<br /> obtuse peak formed in combination of middle however seem disappeared in PANI-Ni film. It<br /> peaks in the cyclic voltammetry of PANI reported may be consisted with the presence of<br /> in [14]. It signifies that there is coexistence of nanoclusters of nickel in PANI-Ni film. The<br /> reactions between nitronium aniline cation mentioned changes show the change in popula-<br /> (C4H5NH+) and the nitronium in PANI matrix tion of charge carriers in PANI-Ni film in<br /> ( C6H4N+ ), and of reaction between PANI comparing with those in PANI film. It is a main<br /> chains itself, through the substitution of a reason to cause the broadening and shift of the<br /> nitronium cation in another PANI chain. On the first anodic wave in cyclic voltammogram, and<br /> other words, the transform from emeraldine to the second peak seems shifted to the higher<br /> pernigraniline occurred simultaneously with the potential, which is out of the studying potential<br /> formation of charge carriers of PANI consisting range (Fig. 3 a - c). Further studies in order to<br /> of polaron and bipolaron forms delocalized on elucidate the influence of nickel in PANI-Ni film<br /> PANI chains. By such cross-linking reactions are going to show in the next paper.<br /> <br /> <br /> <br /> <br /> Figure 3: Multi-cyclic voltammograms of PANI-Ni films consisting of a layer of<br /> nanoclusters of nickel (a), of two layer of nanoclusters of nickel (b) and<br /> three (c), and of no layer of nanoclusters of nickel (d)<br /> <br /> 239<br />  A B<br /> <br /> <br /> <br /> <br /> Figure 4: SEM photographs of PANI films in magnification of 10,000 (A), and of<br /> PANI-Ni film in magnification of 10,000 (B)<br /> <br /> IV - ConclusionS R. M. Hirohashi. J. Electroanal. Chem.,<br /> Vol. 426, P. 97 (1997).<br /> A new concept in structural morphology<br /> 4. M. Zhou, J. J. Xu, H. Y. Chen, and H. Q.<br /> was suggested and developed for conductive<br /> Fang. Electroanalysis, Vol. 9, P. 1185 (1997).<br /> organic polymer composites containing nano-<br /> clusters of metals and nanoparticles. The 5. N. Oyama, J. M. Pope, T. 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