Hemin-Modified Halloysite Nanotube as Electrocatalyst for the Enhanced Electrochemical Determination of Nitrite

Halloysite is naturally occurring nanotubular clay with a phyllosilicate structure and widely used as solid support to modify various redox mediators. We prepared a hemin modified halloysite (Hemin/HNT) by a simple impregnation method, in which a known amount of halloysite was dispersed in ethanolic solution of 1% hemin and reacted for 12 h. The resulting pure Hemin/HNT was employed as electrocatalyst for the electrochemical oxidation of nitrite by cyclic voltammetry. The coverage of hemin molecule over the nanotubular halloysite was confirmed by TGA, FT-IR, XRD and XPS studies. The electron transfer behavior of Hemin/HNT was studied by CV and EIS. It was noted that hemin/HNT modified GCE showed two-fold enhanced oxidation peak current for nitrite with a peak potential of + 0.8 V vs Ag/AgCl in 0.1 M PBS. For a quantitative electrochemical analysis of nitrite ion at the trace levels the differential pulse voltammetry (DPV) and amperometry methods were used based on hemin/HNT modified GCE. A linear calibration plot was constructed by plotting the peak current against the concentrations of nitrite in the ranges of 0.6 × 10 −6 M to 24.6 × 10 −5 M, (R 2 = 0.9968) and 0.6 × 10 −8 to 43.3 × 10 −7 M (R 2 = 0.9996) and the detection limit was found to be 42 and 43 nM with a sensitivity of 23.55 and 22.96 μ A. μ M −1 .cm −2 by DPV and amperometry, respectively. The repeatability of the proposed sensor evaluated in terms of relative standard deviation of 1.7% for 5 measurements (3.3 × 10 −6 M) nitrite. The inference effect of various anions and cations on nitrite oxidation peak current was studied by amperometry method. A stable and reliable current response was obtained for nitrite analysis in water samples.