Electrochemical Properties and Analytical Applications of Keggin-type Phosphomolybdic Anions in Electrostatically Linked 2-Aminoethanethiol Self-Assembled Monolayers

Abstract.

A composite film containing a heteropolyanion was prepared on a 2-aminoethanethiol (AT) self-assembled monolayer film-modified gold electrode by attaching the Keggin-type phosphomolybdic anion. The surface structures and electrochemical properties of the composite films were characterized by using ATR-FTIR, AC impedance, cyclic voltammetry and chronocoulometry. FTIR studies indicated that there was some electrostatic interaction between Pmo₁₂O₄₂⁷⁻ and surface NH₃⁺. Three reversible redox couples were observed in 1.0 mol L⁻¹ H₂SO₄ in the potential range of 0–0.7 V for the composite film modified electrode, which were attributed to two-electron and two-proton electrochemical processes of PMo₁₂O₄₂⁷⁻. The diffusion coefficient is determined to be 2.04×10⁻⁷ cm² s⁻¹. The composite film shows good catalytic activities for the reduction of nitrite (NO₂⁻) in acidic solution and the catalytic mechanisms are described. The modified electrode provides a linear response for NO₂⁻ in the concentration range of 1.0×10⁻⁴ to 1.0×10⁻⁷ mol L⁻¹ by differential pulse adsorptive stripping voltammetry with a correlation coefficient of 0.9965. The detection limit (three times the signal blank/slope) was 2.0×10⁻⁸ mol L⁻¹. The modified electrode was used for the determination of NO₂⁻ in wastewater.