The influence of pH on electrochemical behavior of nicotine-clay based electrodes

Abstract

Montmorillonite based clay was acid activated. Nicotine was adsorbed on untreated and acid activated clay from its aqueous solution at either pH=6 or pH=9.26 (unadjusted pH solution). The XRD analysis revealed that the 001 basal spacing of montmorillonite after nicotine adsorption was around 1.38 nm, regardless of clay treatment or pH of adsorption. The obtained values for basal spacing indicate that nicotine is in monolayer arrangement. In order to investigate electrochemical properties, untreated and acid activated clay, with and without nicotine, were used as modifier of carbon paste electrode. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to study electrochemical response of clay-modified electrodes toward ferrocyanide probe. The nicotine-modified untreated clay used as paste electrode showed enhanced electrochemical response toward ferrocyanide probe in comparison to electrode based on clay without nicotine. On the other hand, adsorbed nicotine on acid activate clay resulted in lower electrode activity. Electrochemical response of adsorbed nicotine was studied at different pH. Nicotine oxidation at each of investigated samples followed the same trend regardless of clay treatment or pH at which adsorption was performed. For all samples, nicotine oxidation peak potential showed linear dependence on pH in pH range from 3.7 to 9.0, with slopes close to the value of 59 mVdec-1 expected for equal number of protons and electrons involved in the reaction. The nicotine reduction process was best resolved at pH = 1 at potential around -1.35 V, while the following cathodic wave observed at potential around -1.5 V was ascribed to the cathodic hydrogen reduction. Mechanism of electrochemical oxidation was not influenced by pH of adsorption, i.e., nicotine form. The amount of adsorbed nicotine was not correlated with the electrochemical activity suggesting that only small number of adsorbed nicotine was involved in electrochemical response.