versión On-line ISSN 0717-9707
J. Chil. Chem. Soc. v.50 n.3 Concepción sep. 2005
J. Chil. Chem. Soc., 50, N° 3 (2005), págs: 613-616
ELECTRODIC POLYMER MATERIALS BASED IN ANILINE. INFLUENCE OF Ni2+, Co2+, AND Cu2+ IONS ON ITS FORMATION
LUIS BASÁEZ1*, PETR VANYSEK2, BERNABÉ L. RIVAS1.
1Faculty of Chemistry of Chemical Sciences, University of Concepción, P.O. Box 160-C, Concepción, Chile. Email: *firstname.lastname@example.org
Behaviour of aniline when voltametrically electropolymerized in the presence of Ni2+, Co2+, and Cu2+ cations has been studies 0.1 mol ·L-1 aniline in the presence of 0.01 mol·L-1 copper(II), nickel(II), and cobalt(II) ions and of three inorganic acids: HCl, HNO3, and H2SO4, was used. Aniline shows that polymerizes in all strong acids and metal ions selected, the reversibility and clarity of the redox processes in the presence of metal ions, indicate that the most accurate conditions for electrosynthesizing polyaniline (Pani) was CuCl2 in 1.0 M HCl; Ni(NO3)2 in 1.0 M HNO3 and in HNO3 1.0 M Co(NO3)2. In all cases, similar voltamograms were obtained and polymer growing changes according to the metal ion used. For Co(II), is more favorable in the following order: H2SO4 > HCl > HNO3. For Ni(II) is H2SO4 > HCl @ HNO3, and for Cu(II) is H2SO4 > HCl @ HNO3.
The aim of this work is to study the effects of metal ions on aniline and their electropolymerization in acid media.
Keywords: Electropolymerization, aniline, metal ion
Polyaniline (Pani), an important member of the class of conjugated conducting polymers, has attracted great attention because of its wide field of potential applications in electronics, electrochemical, and optical properties such us: rechargeable batteries (1-3), sensors (4-6), light emitting diodes (7-8), catalysis (9-10), etc. Besides it is easy to prepare and possesses good thermal as well as environmental stability. To improve the processability and thermal and environmental stabilty and to induce novel electronic and electrochemical properties, substituted Pani are being developed. Dopants also impart desired characteristics in conducting polymers (11).
Because of the development of this polymer, during the last decades the study has been focused in searching its functionallity. There are two ways to achieve this: one is a covalent substitution of the structure and, the second one is using anion exchange properties in the polymer in its oxide form or trapping anionic complexes during the polymer synthesis (12). Moreover, metal anion complexes, such us PtCl6= (13), have been added to Pani. Electrochemical oxidation of aniline encapsulated in a silica solid electrolyte prepared by a sol-gel process yielded products that were dependent on the pore size. An acid-catalyzed process that used tetramethyl orthosilicate as the precursor and aniline as a dopant yielded the silica (14). Incorporation of surface-derivatized gold nanoparticles into electrochemically generated polymer films (8), electrogeneration of polymer films (15), in the presence of Ni(II) (16-17) and using gold electrode (18), ultrathin monolayers and multilayers of polyaniline (19).Recently we have studied the electropolymerization of aniline in different media in presence of Cu(II) (20-23).
For the electrochemical Pani synthesis, the aniline monomer was purified under vacuum by bio-distillation. Reagents used were: Co(NO3)2 x 6H2O, Ni(NO3)2 x H2O, and CuCl2 x 2H2O (Merck. p.a.), HNO3 and HCl (Mallinckrodt p.a.).
A classic three-electrode assembly working electrode: platinum with an area of 0.018 cm2, reference electrode: Ag/AgCl an auxiliary electrode: platinum of wide area in order to trace voltamograms.
Measurements were carried out on a CV-50W interface, coupled to a Cell Stand C3, from Bioanalytical Systems (BAS).
All experiments were performed at 20C, with a purge time of 20 min in a nitrogen environment. Solution pH was kept constant (pH=0), under a 1 M acid concentration. The holder for the solution was 0.1 M KNO3, metal ion concentration 0.01 M and aniline 0.1 M. All voltammetric processes were performed at a constant scanning speed of 100 (mV·S-1) in a range of potential from -300 to 1000 (mV) with a sensibility of 1E-4 (A/V) and a delay time previous to analysis of 2 sec.
RESULTS AND DISCUSSION
The study of 0.1 M aniline in different inorganic acids at 1 M concentration was performed (see figure 1) in the potential interval from -0.30 to +1.00 V is carried out. Three processes in HCl and HNO3 are observed, but in H2SO4, the third process is missed. There is no displacement of potential from anodic and cathodic peaks. Decreasing order of current for aniline in different acid environments is as follows: H2SO4 > HNO3 > HCl. Voltamograms for 0.1 M Pani (see figure 2) in 1.0 M HCl traced in the potential interval from -0.30 to +1.00 V generated three processes: The first one occurs at circa +0.76 V. The second one occurs at +0.26 V and the third process takes place at -0.21 V. In all processes, currents are increased as cycle of time lapses and the reversibility increases. However, when it polymerizes in the presence of 0.01 M Cu(II), the first process decreases its current and the third process disappears. Nevertheless, the second process is affected by a potential displacement of the cathodic peak from +0.11 V to +0.20 V and reversibility improves by increasing the amount of cycles. Probably, this is because the inclusion of the cation into the polymeric network, that would increase the transference processes by forming a conductive metal-polymer. when polimerization tabes place in the presence of Co(II) and Ni(II) (see figure 3), the potential displacement of anodic and cathodic processes is not observed. However, is possible to appreciate that, in all processes under the presence of Co(II), both anodic and cathodic currents increase. Under the presence of Ni(II), anodic and cathodic currents are slightly smoller than those of Pani in HCl. In both Ni(II) and Co(II), the third process, remains.
Pani voltamograms (see figure 3) in 1 M HNO3 traced in the potential interval from -0.30 to +1.00 V generated, just like the previous situation, three processes. The first one, at circa +0.77. The second one takes place at +0.24 V and the third one, occurs at +0.22 V. On the contrary of to the previous case, in the presence of metal ions Cu(II), Co(II) and NI(II), the third process do not disappear and cathodic peak potentials do not show when compared with Pani in HCl. Polimerization with Ni(II), cathodic and anodic currents similar to those of Pani in HNO3 for both, first and second process are ahserved. In the presence of Co(II) and Cu(II), nor anodic neither cathodic largu differences are observed. Pani voltamograms (see figure 3) in 1 M H2SO4 traced in the potential interval from -0.30 to +1.00 V show two processes. The first one occurs at +0.80 V and the second process, takes place at +0.27 V. Unlike to previous acid environments, in the presence of metal ions Cu(II), Co(II), and NI(II), the third process does not occur. Variations in the peaks of cathodic potentials on the first process from +0.72 V to +0.51 V, are observed. In the second process, there is a displacement from +0.27 V to +0.29 V. No displacements with Ni(II) and Cu(II) are observed.
Decreasing order of anodic and cathodic current for both processes is as follows: Co(II) > Cu(II) > Ni(II). Signal in current of Co(II) exceeds due signal obtained with Pani in H2SO4.
It has been showon that aniline polymerizes in all strong acids selected HCl, HNO3, and H2SO4 in the presence of divalent cations nickel and cobalt. In all cases, similar voltamogrames were obtained. Nevertheless, polymer growing changes according to the metallic ion are produced. The most accurate to electrosynthesize polyaniline (Pani) was CuCl2 in 1.0 M HCl; Ni(NO3)2 in 1.0 M HNO3, and Co(NO3)2 in 1.0 M HNO3. For Co(II), it is more favorable in the following order: H2SO4 > HCl > HNO3. For Ni(II) is H2SO4 > HCl @ HNO3, and for Cu(II) is H2SO4 > HCl @ HNO3.
The authors thank to FONDECYT (Grant Líneas Complementarias No 8990011), DIUC No. 203.021.017-1.0 and Fundación Andes for the financial support.
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