Navegando por Palavras-chave "Self-assembled films"

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    Desenvolvimento de filmes automontados baseados em compósitos de poli (orto-etoxianilina) e nanotubos de carbono
    (Universidade Federal de São Paulo, 2018-12-07) Soares, Vinicius Bianchi [UNIFESP]; Simões, Fabio Ruiz [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    Materials such as conductive polymers and carbon nanotubes are considered as promising materials for several applications, among them the development of electrodes in charge storages as well as sensors due to their characteristics such as electrical conductivity, decrease of oxidation potential, enhance of reaction speed and so forth. Conductive polymers have as advantage their electrical conductivity that can be modulated by oxidation reactions and by interactions with electron acceptors and donors, while carbon nanotubes can promote electron transfer reactions, increase the reaction rate and decrease oxidation potentials. When combined, these materials show synergy of their properties. Thus, this project aimed at the synthesis and characterization of conductive composites by the in-situ polymerization of poly (ortho-ethoxyaniline), a derivative of the polyaniline, with carbon-functional multilayered carbon nanotubes with different mass fractions, as well as to produce and characterize modified electrodes by evaporation (casting) and by the process of self-assembling on substrates of glass covered with indium oxide and tin. The electrodes produced were characterized using the techniques of Cyclic Voltammetry, Electrochemical Impedance Spectroscopy, UV-Visible Spectroscopy and Scanning Electron Microscopy. The results showed that the electrodes modified with composites showed synergism of properties by the increase of the current signals of the polymer and decrease of the capacitive current as well as by the decrease of the resistance to the transfer of charge.
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    Desenvolvimento de filmes automontados baseados em compósitos de polipirrol e nanotubos de carbono para o monitoramento de pesticidas em ambiente marinho
    (Universidade Federal de São Paulo, 2017-03-24) Araujo, Gabriela Martins de [UNIFESP]; Simões, Fabio Ruiz [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    The development of sensor materials for the monitoring of endocrine disruptors substances such as pesticides, using electroanalytical methods like voltammetric techniques, have low cost and time analysis as advantages as well as offering the possibility of in-situ monitoring. Conducting polymers have as their main characteristic the electrical conductivity which can be regulated in a wide range, through interactions with acceptor and donors of electrons, which makes them attractive as transducers or active. Among the different conducting polymers the Polypyrrole is one of the most studied in the development of sensors. Already the carbon nanotubes have the ability to promote electron transfer reactions, increasing reaction speed and decreasing oxidation potentials. Thus, materials based on conducting polymer composites and carbon nanotubes have been developed and present synergistic properties like the increase of sensitivity and selectivity in relation to its separate materials. The aim of this work was to develop and characterize self-assembled films based on Polypyrrole and carbon nanotubes composites deposited on substrates of glass covered with indium-tin oxide and carbon screen-printed electrodes to monitor Diuron and Chlorothalonil pesticides which are commonly used in marine environment. The self-assembled films were characterized using the techniques of Cyclic Voltammetry, Electrochemical Impedance Spectroscopy, UV-Visible Spectroscopy and Scanning Electronic Microscopy. The applicability of the sensors was evaluated using the electroanalytical techniques of Square Wave Voltametry and Differential Pulse Voltammetry. The results showed the composite film on printed electrode substrate had more definite voltammetric peaks due to the synergism between the Polypyrrole and the carbon nanotubes resulting in an increase of the polymer currents, the reduction of the capacitive current and the decrease of the transfer resistance of load. The results of the applicability showed the composite film in printed electrode presented better sensitivity compared to the film of Polypyrrole due to the carbon nanotubes in their structure in the presence of the pesticide Diuron detecting this herbicide in oxidation potential of 0,58V being smaller than the potential already known in the literature that is around 1,1V. The LOQ and LOD were respectively 2,584. 10-6 mol.L-1 and 7,83.10-7 mol.L-1 for the analytical curve for the peak at 0,58V on the printed electrode made from the composite film.
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    Layer-by-layer assembly of functionalized reduced graphene oxide for direct electrochemistry and glucose detection
    (Elsevier Science Bv, 2016) Tavares Mascagni, Daniela Branco; Miyazaki, Celina Massumi; da Cruz, Nilson Cristino; Moraes, Marli Leite de [UNIFESP]; Riul, Antonio, Jr.; Ferreira, Marystela
    We report an electrochemical glucose biosensor made with layer-by-layer (LbL) films of functionalized reduced graphene oxide (rGO) and glucose oxidase (GOx). The LbL assembly using positively and negatively charged rGO multilayers represents a simple approach to develop enzymatic biosensors. The electron transport properties of graphene were combined with the specificity provided by the enzyme. rGO was obtained and functionalized using chemical methods, being positively charged with poly(diallyldimethylammonium chloride) to form GPDDA, and negatively charged with poly(styrene sulfonate) to form GPSS. Stable aqueous dispersions of GPDDA and GPSS are easily obtained, enabling the growth of LbL films on various solid supports. The use of graphene in the immobilization of GOx promoted Direct Electron Transfer, which was evaluated by Cyclic Volt-ammetry. Amperometric measurements indicated a detection limit of 13.4 mu mol.L-1 and sensitivity of 2.47 mu A.cm(-2). mmol(-1).L for glucose with the (GPDDA/GPSS)(1)/(GPDDA/GOx)(2) architecture, whose thickness was 19.80 +/- 0.28 nm, as determined by Surface Plasmon Resonance (SPR). The sensor may be useful for clinical analysis since glucose could be detected even in the presence of typical interfering agents and in real samples of a lactose-free milk and an electrolyte solution to prevent dehydration. (C) 2016 Elsevier B.V. All rights reserved.
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    Self-assembled films based on polypyrrole and carbon nanotubes composites for the determination of Diuron pesticide
    (Springer, 2018) Araujo, Gabriela Martins de [UNIFESP]; Simões, Fabio Ruiz [UNIFESP]
    In this work, polypyrrole (PPy) and its respective composite with functionalized multi-walled carbon nanotubes (MWCNT) were obtained by chemical polymerization of the monomer pyrrole in aqueous solution. The obtained PPy as well as its composite (PPy-MWCNT) were characterized by Fourier transform infrared spectroscopy (FTIR) and were used to produce nanostructured self-assembled (SA) films deposited onto glass substrates covered with indium tin oxide (ITO). The SA films were produced with alternated layers of polystyrene sulphonated (PSS) and were characterized by UV-visible, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) analyses. The applicability of the SA films was evaluated by square wave voltammetry (SWV) with standard additions of aliquots of Diuron pesticide in Britton-Robinson buffer solutions (pH = 2.0). The results showed an oxidation peak at 0.23 V which increases in function of the Diuron concentration for both the SA films. It was also observed that the SA film based on the composite (PPy-MWCNT/PSS) showed a peak current intensity about ten times higher in comparison with its unmodified counterpart (PPy/PSS) for a Diuron concentration of 4.29 x 10(-5) mol L-1, indicating a synergic effect between PPy and MWCNT in the composite. The limits of quantification (LOQ) and limits of detection (LOD) were respectively 8.6 x 10(-7) mol L-1 and 2.6 x 10(-7) mol L-1.