Study of the composite electrodes carbon–polyvinyl chloride and carbon–polyvinyl chloride/Nafion by ex situ and in situ methods
Introduction
The electrochemical pretreatment of glassy carbon electrodes [1], [2], [3], carbon film electrodes [4], carbon paste electrodes [5], basal and edge pressure annealed pyrolytic graphite [6], [7], [8], [9] and composites based on conductive phases dispersed in polymeric matrices [10], [11], [12], [13] are recommended in order to obtain reproducible electroanalytical results, enhanced electroactivity or selectivity. These methods of pretreatment frequently cause changes to the surface composition, the surface roughness, the production of surface-bound functional groups or the intercalation compounds owing to the insertion of ions, atoms and molecules into its interplanar space [14], [15]. These pretreated or modified electrodes are commonly used in electroanalysis, biosensors, electrochromism and electrocatalysis [16], [17]. However, the nature and reactivity of the electrode surface depends on the structure, texture and shape of the carbon material when it is used as an electrically conducting part of a composite material. Although conductor–polymer composites are being increasingly used in electrochemistry, carbon–polyvinyl chloride (C–PVC) composites are rarely used in voltammetric analysis [18], [19], [20] due to difficulties in electrode preparation such as the pellet compression technique. In this article we demonstrate that the C–PVC composite electrodes can be prepared by hand pressure-molding. This preparation method in comparison with the compression technique is easier, economical and produces larger ‘real surface area/apparent electrode area’ ratios. For the present paper, the electrochemical response of C–PVC and C–PVC coated with Nafion composites was studied using differential pulse voltammetry (DPV) and cyclic voltammetry (CV). To obtain renewable surfaces, piston-like systems and Teflon-tube packing procedures were used for electrode preparation.
According to previous investigations [18], [19], [20] into graphite–PVC composites, a homogeneous electrode embedded in a flow-through cell is obtained after drying. Under the given conditions the graphite–PVC electrode lacked long-term stability, and so the electrode surface was not analyzed after electroanalytical work. We used ex situ techniques such as scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM) to study the morphology, topography and composition of the electrode surface before and after the application of repetitive triangular potential sweep (RTPS) in 0.1 N HClO4, H2SO4 and LiClO4. In order to test the effect of the surface changes on the sensitivity and selectivity of the electrode we performed pre-activation by cycling and modification with ruthenium phenanthroline complex was performed. The pretreated C–PVC electrode was applied for the determination of dopamine (DA) in acidic and phosphate buffer solutions (pH 7.4) in the presence of ascorbic acid (AA), and the response was compared with that of a glassy carbon electrode.
Section snippets
Chemicals and electrode preparation
The C–PVC and C–PVC/Nafion composite samples were prepared following the procedure described in detail elsewhere [21] using polyvinyl chloride (PVC) powder (Fluka), finely pulverized spectral carbon (Elektrokohle Lichtenberg, Berlin, Germany), and Nafion solution (Aldrich). For the electrochemical study of these composite samples as electrodes, the resulting paste was packed into a Teflon tube or a cylinder (piston-like system comprising an 8 cm long Teflon tube with an internal diameter of 2
Ex situ characterization of the C–PVC composites
The electrical resistivity of the C–PVC composite samples prepared according to the procedure reported elsewhere [21] was 0.1–10 Ω cm. We consider that the conductive network is composed of aggregates with low electrical resistance (carbon particles with a very thin layer of the composite polymer PVC or PVC–Nafion) and of polymeric PVC gaps of different thicknesses.
The morphological study of freshly prepared C–PVC samples by SEM and AFM showed that their surface is very rough, irregular, and
Conclusions
Carbon–polyvinyl chloride and its modified form using Nafion provide a fast, economical way of preparing a suitable electrode for electroanalytical purposes. The electrode surfaces can be varied from micro- to macroscale dimensions and can be formed in various shapes such as rods or thin plates. The composite material shows good resistance to the strong acidic and alkaline solutions as well as organic solvents generally used in electroanalysis. The C–PVC raw composite material has to be
Acknowledgements
M.M. Dávila gratefully acknowledges CONACyT and DAAD for the research fellowships, C. Vázquez and R. Fragoso (CINVESTAV) for the AFM analysis and R. Silva (IF-BUAP) for the SEM and EDS study.
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