Wells-Dawson type polyoxometalate, [S2W18O62]4--doped poly (3,4-ethylenedioxythiophene) films: Voltammetric behaviour and applications to selective bromate detection

Wells-Dawson type polyoxometalate (POM) [(n-C3H7)4N]4S2W18O62 (S2W18) was successfully immobilised with a conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), by chronocoulometry technique. The immobilised films with different surface thicknesses were characterised by various elec-trochemical techniques. The S2W18-doped PEDOT film gave four couples of redox waves, the first one corresponds to the redox process of the polymer itself and the other three couples are electron transfer at tungstate in the framework. The films exhibited inherent pH-dependent redox activity and stability of S2W18 in the thin layer up to 100 mV/s. Only slight changes were observed in the magnitude of peak currents after continuous redox cycling, indicating the relative stability of the S2W18 in the conducting PEDOT. The conductive behaviour of the film was investigated with electrochemical impedance spectroscopy. The study of electrochemical bromate ion sensing based on S2W18-doped PEDOT film employing chronoamperometric technique revealed that at an applied potential of-0.1 V, the S2W18-doped PEDOT film can detect bromate at concentrations between 100 & mu;mol L-1 and 2000 & mu;mol L-1. Moreover, the S2W18-doped PEDOT film shows a detection limit of 4 & mu;mol L-1 without interference from other common ions present in the water. Hybrid films exhibit significant catalytic activity with high selectivity at a low reduction potential of-0.1 V. Chemico-physical characterization of the target systems was performed using atomic force microscopy, field emission scanning electron mi-croscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy.