Browsing by Author "del Valle, M. A."

Now showing 1 - 9 of 9
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    Capacitors Based on Polypyrrole Nanowire Electrodeposits
    (2022) Ramirez, A. M. R.; del Valle, M. A.; Ortega, E.; Diaz, F. R.; Gacitua, M. A.
    The electrochemical polymerization of polypyrrole nanowires is carried out using potentiodynamic and galvanostatic methods in order to enhance the performance of the modified electrodes as capacitor devices. The electrochemical, spectroscopic, and morphological properties are determined through cyclic voltammetry, Raman spectroscopy and scanning electron microscopy, respectively, corroborating the presence of PPy-nw in dimensions of 30 nm in diameter. Characterization as a capacitor revealed that the nanowire structure enhances key parameters such as specific capacitance with 60 times greater value than bulk polymer modification, in addition to a significant increase in stability. In this way, it is verified that electrodes modified with polypyrrole nanowires obtained in situ by electrochemical methods constitute an excellent candidate for the development of capacitors.
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    Effect Of Ultrasound Irradiation in Nucleation and Growth Mechanisms of Poly-o-Anisidine and Polyaniline
    (2013) del Valle, M. A.; Romero, M.; Diaz, F. R.; Armijo, F.; del Rio, R.; Nunez, I.; Dalchiele, E. A.
    The current work studies the effect of ultrasound on nucleation and growth mechanisms (NGM) from the respective i-t transients obtained during the electro-polymerization of ortho-anisidine (OAN) and aniline (ANI), using a potentiostatic (potential step) approach. To this end, optimum electro-synthesis working conditions were searched for using cyclic voltammetry in the presence and absence of ultrasound radiation. The results revealed that ultrasonic disturbance has no effect on the oxidation potential of the starting units. In addition, i-t transients recorded at controlled potential are complex and their deconvolution revealed that both monomers studied herein consist of three contributions. However, it is noteworthy that when the system was irradiated with ultrasound, the respective NGM was not modified, since the same contributions are retained, only the time at which they are defined and the proportion with which each of them contributes to the total charge are altered. It was verified that the contribution most affected by ultrasound was that with diffusion-controlled growth, which is consistent with the morphology changes of the obtained polymeric deposits and the respective increase in the recorded currents during its electro-synthesis; this was explained by means of the proposed model of electro-polymerization based on oligomers solubility at the electrode/solution interface.
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    Electrochemical in situ synthesis of polypyrrole nanowires
    (2019) Ramirez, A. M. R.; Gacitua, M. A.; Ortega, E.; Diaz, F. R.; del Valle, M. A.
    Modification with polypyrrole nanowires, PPy-nw, is accomplished directly upon the working electrode by electrochemical polymerization methods using mesoporous silica as a template. The silica template is prepared by a potentiostatic method, generating a homogeneous film over a previously deposited thin layer of PPy, so that PPy-nw grows within the nanochannels of the mesoporous silica and adheres firmly to the surface. Subsequently the template is removed to obtain intact Pt vertical bar PPy-nw with stable and reproducible electrochemical properties, and with an enhanced (about 360 times higher charge capacity) response after charge-discharge experiments compared to equivalent electrodes modified with polymer deposits in the bulk (PPy) form. SEM reveals the brush-type conformation of PPy-nw (30 nm in diameter). Thus, a cheap, simple, highly repeatable method is used in situ to prepare electrodes modified with nano-structured polymers, using electrochemical techniques alone. This could have a great impact on a wide range of applications of conducting polymers.
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    New Polymers Based on 2,6-di(thiophen-2-yl) aniline and 2,2 '-(thiophen-2,5-diyl) dianiline Monomers. Preparation, Characterization and Thermal, Optical, Electronic and Photovoltaic Properties
    (ESG, 2012) Jessop, I. A.; Zamora, P. P.; Diaz, F. R.; del Valle, M. A.; Leiva, A.; Cattin, L.; Makha, M.; Bernede, J. C.
    A new series of polymers, chemically and electrochemically obtained from monomers containing aniline and thiophene moieties, has been prepared. The purpose is to use them as electron donor layers in the fabrication of dual-layer organic solar cells. Both the monomers and the polymers were characterized using techniques such as NMR, FT-IR, cyclic voltammetry, etc. It was found that polymer growth occurred only through aniline unit(s) and not through thiophene unit(s), as might also be expected. Optical and electronic studies revealed that the products displayed properties suitable for use in photovoltaic devices. However, prepared prototypes yields ranged just between 10(-2) and 10(-3).
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    Nucleation and growth mechanisms during electropolymerization of substituted 3-alkylthiophenes
    (ELSEVIER, 2008) Soto, J. P.; Diaz, F. R.; del Valle, M. A.; Velez, J. H.; East, G. A.
    In the present work the electrochemical study of compounds based on 3-((omega-bromoalkyloxy) methyl) thiophene, varying the length of the alkyl chain between 6 and 12 carbon atoms, is reported. Electropolymerization of the monomers was achieved by potentiodynamic (cyclic voltammetry, CV) and potentiostatic (constant potential) techniques. Voltammograms obtained by CV show that all monomers can be electrochemically oxidized at potentials about 1800 mV to synthesize the respective polymer. Besides, the potential shifts to more anodic potentials on successive scans, increasing thus the resistivity of the material. Nucleation and growth mechanism (NGM) of electropolymerization was investigated by a potentiostatic technique (j-t). Deconvolution of the current-time transient data fitted with a theoretical model suggests that at short times the instantaneous nucleation with two-dimensional growth (IN2D) contribution prevails, followed by an instantaneous nucleation with three-dimensional growth controlled by the charge transfer (IN3Dct) contribution and, finally at longer times, the instantaneous nucleation with three-dimensional growth controlled by diffusion (IN3Ddif) contribution becomes important. The predominance of each contribution to the NGM depends on the monomer being electropolymerized, and the electrolysis time. The morphology predicted from these NGMs fully correlates with that determined by SEM. (C) 2007 Elsevier B.V. All rights reserved.
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    Selective electrochemical determination of dopamine, using a poly(3,4-ethylenedioxythiophene)/polydopamine hybrid film modified electrode
    (2013) Salgado, R.; del Rio, R.; del Valle, M. A.; Armijo, F.
    The selective determination of dopamine (DA) was performed in the presence of ascorbic (AA) and uric acid (UA), using a platinum electrode (Pt) modified with a hybrid film of poly(3,4-ethylenedioxythiophene)/polydopamine (PEDOT/PDA). PEDOT was obtained using a potential step technique on a bare Pt electrode. PDA was subsequently obtained on the PEDOT coated electrode by cyclic voltammetry. The PDA thickness effect allows observing just the DA oxidation signal in the presence of some interferents, e.g. uric acid (UA) and ascorbic acid (AA). The formed PEDOT/PDA hybrid film was compared with PEDOT in a K-4[Fe(CN)(6)] solution in PBS of pH 7.4. Inhibition of the [Fe (CN)(6)](4-)/[Fe(CN)(6])(3-) redox couple on the PEDOT/PDA surface was observed, indicating the film bears a negative surface charge. The different electrodes were characterized by SEM and FTIR. DA amperometric determination was performed in the presence of AA and UA. The sensor proved to be selective toward DA. Calibration curves, with a linear range 1.5 x 10(-6) to 50 x 10(-6) mol L-1, enabled the limit of detection and quantification to be determined, namely 0.65 x 10(-6) mol L-1 and 1.77 x 10(-6) mol L-1, respectively. The described methodology permits, therefore, to propose this modified electrode as a new electrode for DA determination in the presence of interferents. (C) 2013 Elsevier B.V. All rights reserved.
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    Use of fluorine-doped tin oxide electrodes for lipoic acid determination in dietary supplements
    (2012) Miranda, M. P.; del Rio, R.; del Valle, M. A.; Faundez, M.; Armijo, F.
    This paper reports a novel application of fluorine-doped tin oxide electrodes (FTO). To this purpose, electrochemical oxidation mechanism of lipoic acid (LA) at different pHs in the presence of interferents was investigated. FTO displayed electroactivity toward LA oxidation at pH 2. The results indicated that interference from water soluble interferents, derived from excipients or other components coming from dietary supplements, is completely removed with the use of FTO. Square-wave voltammetry, SWV, studies have been shown that at pH 2 an anodic peak at about 0.95 V vs. Ag/AgCl, KCl(sat'd) appears. It was also demonstrated that LA oxidation is diffusion-controlled, involving two electrons in the overall process. From these results, a FTO-based electrode was proposed as LA sensor. SWV was the technique of choice for LA quantitation. A linear range between 5 and 500 mu mol L-1 was found. These results allowed postulating FTO as a potential candidate for the electrochemical determination of LA in the presence of interferents contained in pharmaceutical samples of supplementary diet. (C) 2012 Elsevier B.V. All rights reserved.
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    UV-VIS SPECTROELECTROCHEMICAL IN SITU STUDY DURING THE ELECTROSYNTHESIS OF COPOLYMERS
    (2019) del Valle, M. A.; Motheo, A.; Ramirez, A. M. R.
    In this work, the synthesis of poly(aniline-co-o-methoxyaniline) is performed using purely electrochemical techniques, coupled to UV-vis spectroscopy in situ, in 3D. The electrocopolymerization is carried out on ITO electrodes, in various monomer ratios aniline/o-methoxyaniline varying between 0.1 to 0.4 mol L-1 in H2SO4 1.0 mol L-1 The homo- and copolymers were characterized by cyclic voltammetry, in situ UV-Visible, and scanning electron microscopy. The results show the important information provided by UV-Visible spectroscopy coupled with electrochemical techniques. Thus, it is observed that the reactivity that gives the o-methoxy group in the aniline ring, damages the conductivity of the polymer, due to the occlusion of oligomers of N-phenyl-1,4-benzoquinonediimine and/or with the structure of oxazine. On the other hand, the SEM images show morphological changes associated with the progress of the synthesis, which can be related with the less conductivity produced by o-methoxy, despite the greater reactivity.
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    ZnO thin films fabricated by chemical bath deposition, used as buffer layer in organic solar cells
    (ELSEVIER SCIENCE BV, 2009) Lare, Y.; Godoy, A.; Cattin, L.; Jondo, K.; Abachi, T.; Diaz, F. R.; Morsli, M.; Napo, K.; del Valle, M. A.; Bernede, J. C.
    ZnO thin films synthetized by chemical bath deposition are used as buffer layer between the anode and the organic electron donor in organic solar cells. Films deposited from zinc nitrate solutions are annealed in room air at 300 degrees C for half an hour. The X-ray diffraction and microanalysis studies show that ZnO polycrystalline thin films are obtained. The solar cells used are based on the couple copper phthalocyanine as electron donor and (N, N-diheptyl-3,4,9,10-perylenetetracarboxylicdiimide-PTCDI-C7) as electron acceptor. It is shown that the presence of the ZnO buffer layer improves the energy conversion efficiency of the cells. Such improvement could be attributed to a better energy level alignment at the anode/electron donor interface. The anode roughness induced by the ZnO buffer layer can also transform the planar interface organic electron donor/electron acceptor into roughen topography. This increases the interface area, where carrier separation takes place, which improves solar cells performances. (C) 2009 Elsevier B. V. All rights reserved.