Ammonium heptamolybdate preloaded on flexible carbon-matrix film electrode for the electrochemical phosphate sensor in a river water sample

Abstract

This work designed ammonium heptamolybdate (AHM) preloaded on a polyaniline (PANI)/coconut shell-derived carbon (CC)/poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF) composite flexible film electrode. The as-prepared novel AHM@PANI/CC/PVDF composite film electrode allowed to the selective and sensitive determination of phosphate in river water samples. The optimized AHM@PANI/CC/PVDF film delivered excellent ionic conductivity (6.58 × 10−5 S cm−1). The analysis of the flexible composite matrix film confirmed the presence of three AHM redox couples, and their formal potential, peak potential difference, and surface coverage (τ) were calculated. The AHM@PANI/CC/PVDF film comprised an excellent microenvironment for phosphate (H2PO4−) detection, while the resulting electroactive phosphomolybdic complex species were stabilized by the composite matrix. The product of phosphomolybdic complex was electrochemically reduced at +0.25 V vs. saturated calomel electrode (SCE). The Keggin-type phosphomolybdic complex on the composite film was ex-situ examined by elemental mapping, X-ray diffraction pattern and X-ray photoelectron spectroscopy. From the spectroscopic studies individual composite materials interaction with molybdate mechanism provided. The AHM@PANI/CC/PVDF film electrode revealed a good phosphate detection concentration range of 10–114 µM, and it exhibited a low detection limit (0.6 µM). Besides, AHM@PANI/CC/PVDF was used to analyze a tap and river water sample and validated the obtained data through the spectrophotometric method which yielded an excellent recovery range (101.3%–113.3%).