Preparation and electrocatalytic oxidation properties of a nickel pentacyanonitrosylferrate modified carbon composite electrode by two-step sol-gel technique: improvement of the catalytic activity

The sol-gel technique was used to construct nickel pentacyanonitrosylferrate (NiPCNF) modified composite ceramic carbon electrodes (CCEs). This involves two steps: forming a CCE containing Ni powder and then immersing the electrode into a sodium pentacyanonitrosyl-ferrate solution (electroless deposition). The cyclic voltammograms of the resulting surface modified CCE under optimum conditions show a well-defined redox couple due to the [(NiFeIII/II)-Fe-II(CN)(5)NO](0/-1) system. The electrochemical properties and stability of the modified electrode were investigated by cyclic voltammetry. The apparent electron transfer rate constant (k(s)) and transfer coefficient (alpha) were determined by cyclic voltammetry being about 1.1 s(-1) and 0.55, respectively. Sulfite has been chosen as a model to elucidate the electrocatalytic ability of NiPCNF-modified CCE prepared by one- or two-step sol-gel technique. The modified electrode showed excellent electrocatalytic activity toward the SO32- electro oxidation in pH range 3-9 in comparison with CCE modified by homogeneous mixture of graphite powder, Ni(NO3)(2) and Na-2[Fe(CN)(5)NO] (one-step sol-gel technique). Sulfite was determined amperometrically at the surface of this modified electrode in pH 7. Under the optimized conditions the calibration curve is linear in the concentration range 2 muM to 2.0 mM. The detection limit (signal-to-noise is 3) and sensitivity are 0.5 muM and 13.5 nA/muM. The modified carbon ceramic electrode containing nickel pentacyanonitrosylferrate shows good repeatability, short response time, t (90%) <2 s, long-term stability (3 months), and it is renewed by simple mechanical polishing and its immersing in Na-2[Fe(CN)(5)NO] solution. The advantages of the SO32- amperometrically detector based on the nickel pentacyanonitrosylferrate-doped CCE is high sensitivity, inherent stability at wide pH range, excellent catalytic activity and less expense and simplicity of preparation. This sensor can be used as amperometric detector in chromatographic instruments. (C) 2003 Elsevier Ltd. All rights reserved.