Synthesis, characterization and performance of polyaniline–polyoxometalates (XM12, X = P, Si and M = Mo, W) composites as electrocatalysts of bromates

Composite materials of the type polyaniline (PANI)–polyoxometalates (POM = XM12, X = P, Si and M = Mo, W) were synthesized and characterized by means of FT-IR, UV–vis, SEM, XRD, SAXS analysis and cyclic voltammetry. Suspensions of 2.5 mg mL−1 PANI–PMo12 in 2% (w/v) poly(ethyleneimine) (PEI) in methanol were prepared and deposited onto graphene oxide-modified graphite electrodes. These were tested as sensors for the ability to electrocatalyze the reduction of bromates by using cyclic voltammetry. Various experimental variables such as the loading of the composite material, the concentration of PEI, the pH and the composition of electrolyte, and the electrode material were optimized. By performing DC amperometry at a fixed potential of −0.3 V, versus a Ag/AgCl reference electrode, in 0.05 M HCl, a linear calibration curve over the concentration range 7.5 × 10−6 to 5.0 × 10−4 M BrO3− was constructed. The 3σ limit of detection and the relative standard deviation of the method were 3.0 × 10−6 M BrO3− and 3% (n = 7, 1 × 10−4 M BrO3−), respectively. The accuracy of the method was established by recovery studies in spiked drinking water and flour extract samples. Recovery was 95.4–100.2%. Finally, the sensors exhibited a remarkable working and storage stability when they kept dry in ambient conditions.