Abstract
ZnO and hematite (Fe2O3) nanoparticles (NPs) have been used as electrocatalysts or electron mediators for the modification of gold (Au) electrode for the detection of toxic compounds, i.e., para-nitrophenol (PNP). A comparison of the two types of NPs reveals higher efficiency for ZnO NPs. Electrochemical response measured by three different techniques, i.e., normal cyclic voltammetry (CV), differential pulse voltammetry (DPV), and amperometry, has been used to determine the sensitivity and detection limit of the system. The order of sensitivity varies in the order: amperometry > DPV > normal CV response, both for ZnO and alpha-Fe2O3 NPs. While, the order of detection limit for alpha-Fe2O3 NPs varies as DPV > normal CV > amperometry and for ZnO NPs, the order is normal CV > DPV > amperometry, suggesting that amperometry is the best among all the techniques for detection applications. Based on the electrochemical response, it is proposed that the electrochemical reaction of PNP proceeds via two-step mechanism. In the first step, irreversible reduction of PNP to para-hydroxy nitrophenol takes place with the gain of four electrons and in the second step, reversible redox reaction occurs by the exchange of two electrons, from hydroxy nitrophenol to nitrosophenol and vice versa.