Optimization of the synergistic effects in polycrystalline Pt–Au electrodes in developing an effective arsenic sensor via oxidation reactions

Abstract

A detailed kinetic study of the electrocatalytic oxidation of arsenite [As(III)] to arsenate [As(V)] has been performed in acidic medium by using gold (Au) immobilized platinum (Pt) electrodes. To prepare the Au-modified Pt electrodes, a polycrystalline Pt electrode was cycled between 0 and −1 V vs. Ag/AgCl (sat. KCl) in 0.05 M HAuCl₄ solution at a scan rate of 0.1 V s⁻¹. The Pt–Au electrode prepared by 1 deposition cycle of Au demonstrated an As(III) oxidation peak potential at 0.79 V with a peak current value of 62.14 μA. As the deposition cycle was increased, the required potential for oxidation reaction decreased shifting towards a more negative value. The least potential required was observed for the electrode prepared with 8 deposition cycles of Au. This result was also verified with various surface characterization techniques including SEM, EDX, XRD, and XPS. Kinetic investigation revealed that the As(III) ions approach the 8 cycles of Au deposited Pt electrode through a diffusion-limited process, subsequently following a first-order reaction with stepwise transfer of electrons. The electrode exhibited a sensitivity of 23.13 μA mM⁻¹ for As(III) oxidation. The LOD for As(III) by the proposed electrode was found to be 65.39 μM, which also boasts its excellent performance.