Influence of copper hexacyanoferrate film thickness on the electrochemical properties of self-assembled 3-mercaptopropyl gold electrode and application as a hydrazine sensor
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A copper hexacyanoferrate film was obtained on a modified electrode prepared by self-assembly of 3-mercaptopropyltrimethoxysilane on a gold surface. The film thickness was controlled using a layer-by-layer technique to tune the electrocatalytic properties of the electrode. Two electrodes with different hexacyanoferrate film thicknesses were prepared via three immersions (AuS/CuHCF3) and six immersions (AuS/CuHCF6) of the film in the precursor solutions. Cyclic voltammetry data were obtained to determine the adequate film thickness. Scanning electron microscopy images showed a roughness increase due to the growth of the film thickness at the electrode surface. Electrochemical impedance spectroscopy showed distinct behavior for the two electrodes prepared; while diffusion and charge transfer processes can be observed in both electrodes, an additional capacitive process at intermediary frequencies was observed for the AuS/CuHCF6 electrode. The charge transfer resistance (R ct) for the AuS/CuHCF3 electrode (19.6 Ω cm2) was lower than for AuS/CuHCF6 (27.9 Ω cm2) due to the hexacyanoferrate film thickness, since the charge transfer process demands the simultaneous diffusion of K+ into the surface. Cyclic voltammetry was used to evaluate the application of the AuS/CuHCF3 electrode as an electrochemical sensor, revealing a linear correlation for hydrazine concentrations.
Keywords3-mercaptopropyltrimethoxysilane Gold electrode Self-assembly Copper hexacyanoferrate
F. L. P. thanks FAPEMIG for post-doctoral fellowship (CEX 00202/08). A.M.S.L. is indebted to FAPEMIG (CEX APQ-3716-5.02/07) and Y.G. to FAPESP for financial support. The authors are also indebted to Prof. Claudia Torres for manuscript revision.
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