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Miniaturized pH sensors have attracted the attention mostly due to their applications for monitoring chemical and biological processes. The modification of electrodes by Layer-by-Layer (LbL) technique results in films with nanometric structure for application in devices with different sizes. In this paper, an electrode modified with LbL films of polyaniline-gum Arabic nanocomposite (PANI-GA) and graphene oxide (GO), designed (PANI-GA/GO) 3, was applied as a potentiometric pH sensor based on states of oxidation PANI. The pH measurements were performed in BR buffer solution and a linear range was observed from pH 2 to 7. The detection limit (DL) and quantification limit (QL) were of pH = 0.465 and 1.55, respectively. Analytical curves were obtained in triplicate and inter-assay precision was calculated for the system, demonstrating good results with relative standard deviation (RSD) of 3.7% for five measurements in different days. The (PANI-GA/GO) 3 LbL film showed promising results for its use in the development of potentiometric pH sensor.

The limited availability of fossil fuels and its high environmental impact have caused an increase in the interest in the exploration of alternative sources of energy sources and in the development of devices that are capable of storing this energy for continuous use. Under those perspectives, the preparation of composites materials applicable in the construction of higher efficient supercapacitors have demonstrated a great potential for application as storage devices, based on their structural and electrochemical properties.                 Along these lines, this work describes the development of a methodology to prepare composites materials using graphene oxide (GO) obtained from carbon waste by electrochemical exfoliation and conducting polymers like polyaniline (PAni) and polypyrrol (PPy) through a rapid and simple synthesis.                 The syntheses were basically performed by the in situ polymerization of aniline, pyrrol or both monomers on the oxidized sites of the GO. The followed procedures were a simple adaptation of the method developed by Hou, Y. et al. 2010. At the end of the syntheses, the obtained composites, a fine black powder of GO/PAni or GO/PPy, were structurally characterized by XRD, FTIR, RAMAN e DLS; and electrochemically by CV measurements and charge discharge curves.                 The XRD characterization of the synthesized composites was performed by comparing the diffraction patterns of the materials with the patterns of the individually synthesized components. It was not possible to identify the pattern of PAni in the composite, probably due to the low diffraction intensity and/or the formation of an amorphous layer on the surface of the GO. The confirmation of the formation of the composite was obtained by Raman spectroscopy analysis of the composite and the addition of PAni, PPy or both were identifying as the causers of the lower integrated area ratio between D and G bands compared to pure graphene. This indicate a comparative reduction in the quantity of surface defects due to the anchoring of the conducting polymers. With the aim of identifying the functional groups of different components in the composite structure, they were analyzed by FTIR. The spectrum obtained presented main bands that could be assigned to specific functional groups of the different conducting polymers or GO.                 The CV curves shown a nearly ideal rectangular shape, which indicates a good capacitive behavior with a rapid charging and discharging process and the charge-discharge measurements of the composite obtained indicate a good potential for application in low-cost high performance supercapacitors. The charge-discharge measurements indicated an almost linear slope in the range of applied potential and present quite symmetrical, indicating a characteristic of the capacitive behavior. The electrochemical characterization shows 171 F g-1as specific capacitance value and an improvement in the charge transfer kinetics when the composite is compared with the individual constituent materials.  Acknowledgments:This work was supported by State University of Ponta Grossa (UEPG), Programa Associado de Pós-Graduação em Química - Doutorado, Grupo de Geração e Armazenamento de Energia e Tratamento de Superfícies (GGAETS), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Complexo de laboratórios Multiusuários (ClabMu).  Reference: HOU, Y. et al. Design and synthesis of hierarchical MnO2nanospheres/Carbon nanotubes/Conducting polymer ternary composite for High performance electrochemical electrodes. Nano Lett., v. 10, p. 2727-2733, 2010.