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 x 10(-6) M to 24.6 x 10(-5) M, (R-2 = 0.9968) and 0.6 x 10(-8) to 43.3 x 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 mu A.mu 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 x 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. (C) 2022 The Electrochemical Society (ECS). Published on behalf of ECS by IOP Publishing Limited.

Automated summary

The study involves the preparation of an electrocatalyst by modifying halloysite with hemin for the oxidation reaction of nitrite, resulting in enhanced peak current. Quantitative analysis of trace nitrite levels was achieved using differential pulse voltammetry and amperometry methods, with low detection limits and good repeatability.