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Published on: December 4, 2017
pH dependent electro-oxidation of arsenite on gold surface: Relative kinetics and sensitivity
Mohebul Ahsan1, Muhammad Zobayer Bin Mukhlish2, Nazia Khatun3
1Electrochemistry and Catalysis Research Laboratory (ECRL), Department of Chemistry, School of Physical Sciences, Shahjalal University of Science and Technology, Sylhet 3114, Bangladesh.
Abstract:
A detailed kinetic investigation of As(III) oxidation was performed on gold surface within pH between ∼3.0 and ∼9.0. It was found that the As(III) oxidation on the gold surface follows a purely adsorption-controlled process irrespective of pH. The evaluated adsorption equilibrium constant decreased from 3.21 × 105 to 1.61 × 105 mol L-1 for acidic to basic medium, which implies the strong affinity of the arsenic species in the acidic medium. Besides, the estimation of Gibbs free energy revealed that an acidic medium promotes arsenic oxidation on gold surface. In mechanistic aspect, the oxidation reaction adopts a stepwise pathway for acidic medium and a concerted pathway for neutral and basic medium. From the substantial kinetic evaluation, it is established that a conducive and compatible environment for the oxidation of arsenic was found in an acidic medium rather than a basic or neutral medium on gold surface. Besides, in sensitivity concern, neutral and highly acidic medium is quite favourable for the arsenite oxidation on gold surface.
