Layer-by-layer assembly of tetra-Mn-containing 30-tungsto-4-phosphate, [M4(H2O)2(P2W15O56)2]n− (M = MnII and MnIII) with AuNps-MWCNT: electrochemical detection of iodate

Abstract

This study demonstrates the Layer-by-Layer (LbL) approach to assemble the sandwich structured [M₄(H₂O)₂(P₂W₁₅O₅₆)₂]ⁿ⁻ (M = Mn^II and Mn^III) polyoxometalates (POMs) with gold nanoparticles (AuNps) decorated multi-walled carbon nanotubes (MWCNT) on a carbon electrode. Polyethylenimine has been employed as a base layer prior to the deposition of the AuNps-MWCNT and POM. The multi-layered modified electrodes [AuNps-MWCNT/Mn^II(P₂W₁₅)₂] and [AuNps-MWCNT/Mn^III(P₂W₁₅)₂] have been characterised using electrochemical and surface techniques. Electrochemical impedance spectroscopy data revealed that the addition of AuNps-MWCNT increased the multilayer films' conductivity. The modified electrodes displayed pH dependent redox activity associated with the POM and thin-layer behaviour, as demonstrated by cyclic voltammetry (CV). The stability of the multilayer towards redox cycling through the POM redox processes was found to be good along with the ability of the modified electrode towards the electrocatalytic reduction of iodate. The amperometric investigation of AuNps-MWCNT/Mn^II(P₂W₁₅)₂ multilayer films revealed a linear range of 1–3000 μM with the limit of detection (LOD) and sensitivity was found to be 0.14 μM (S/N = 3) and 0.58 μA cm⁻² μM⁻¹. Similarly, the AuNps-MWCNT/Mn^III(P₂W₁₅)₂ multilayer films showed a linear range of 1–3000 μM with a limit of detection and sensitivity was found to be 0.20 μM (S/N = 3) and 0.90 μA cm⁻² μM⁻¹.