Abstract
The efficacy of the ZnO-alpha-Fe2O3 composites as carbon paste electrode (CPE) modifier for sensitive electrochemical detection of loperamide was explored. The composites were synthesized in 1:1, 2:1, and 3:1 (ZnO:alpha-Fe2O3) ratios by the gradual amalgamation of pre-synthesized alpha-Fe2O3 and hydrated gel of Zn2+ that later transformed to the ZnO by thermal treatment The lattice parameters of the composite ZnO and, the probable variations in the oxidation states of the components during the adopted coating procedure were assessed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The field-emission scanning electron microscopy (FESEM) imaging of the as-synthesized and carbon paste (CP) dispersed composite powders at various resolutions exposed the increased surface coverage of the alpha-Fe2O3 by the ZnO particles with the increasing loading and the uniform distribution of the composite materials in the matrix of carbon paste. Compared to bare CPE, the composites modified CPEs exhibited significantly decreased charge transfer impedance at the electrode/electrolyte interface evaluated by electrochemical impedance spectroscopy (EIS). The sensing ability of the composites modified electrodes for the detection of loperamide in the aqueous medium was investigated. A higher and affectedly improved cyclic voltammetric (CV) oxidation signal of loperamide was noticed at the prepared ZnO:alpha-Fe2O3/CPEs compared to pure components modified CPEs i.e. ZnO/CPE and alpha-Fe2O3/CPE. Based on the EIS and CV investigations, a superior electrochemical performance of (2:1) ZnO:alpha-Fe2O3/CPE was established. Additionally, under optimized experimental conditions of pH, deposition potential, and accumulation time, loperamide was quantified by square wave stripping voltammetry (SWSV) that resulted in the linear calibration ranges from 0.08-1 and 2-10 mu mol L-1 with detection limits (S/N = 3) of 7.9 and 3.6 nmol L-1. The findings of various electrochemical investigations were correlated to establish the mechanism of charge transport and oxidation of loperamide. (C) 2016 Elsevier B.V. All rights reserved.