Electro-Oxidation of Aldehydes in Alkaline Solution by Electropolymerized Nickel Salen-Based Film Modified Electrodes

A glassy carbon electrode modified with poly-nickel hydroxy salen (poly-Ni(OH)salen) film was successfully developed for the electro-oxidation of aldehydes in alkaline media. This film can be prepared in two steps: (i) electropolymerization of N,N'-bis-(salicylidene)ethylenediaminonickel(II), or nickel(II) salen, in acetonitrile containing 0.05 M tetramethylammonium tetrafluoroborate (TMABF4), followed by (ii) film transformation in sodium hydroxide solution. Ultraviolet–visible spectrophotometry and scanning electron microscopy-energy dispersive X-ray (SEM-EDX) spectroscopy were employed to confirm the existence of polymeric nickel salen-based films. Cyclic voltammetry results reveal that the poly-Ni(OH)salen film modified electrode can respond to aldehydes, especially acetaldehyde, by giving anodic peak currents related to their electro-oxidation. Parameters affecting the formation and the electrocatalytic performance of the film were optimized. Under the optimum conditions developed herein, the poly-Ni(OH)salen electrode exhibited good linearity over an acetaldehyde concentration range of 0.25 to 20.0 mM with a detection limit of 0.15 ± 0.05 mM. Using the standard addition method, acceptable recovery percentages of acetaldehyde in liquid milk samples were achieved. Additionally, the stability of the modified electrode during the electro-oxidation process is discussed.