Bifunctional bismuth molybdate/biochar composite with an enhanced photo-assisted electrochemical activity: Memory effect-free Hg(II) detection and efficient photocatalytic reduction of Cr(VI)

Differential pulse anodic stripping voltammetry (DPASV) is one of the widely used methods for measuring heavy metal ions (HMIs). However, the severe memory effects caused by the incomplete oxidation of zero-valent metals during the dissolution process lead to undesirable results of sensitivity and repeatability. To solve this problem, a photo-assisted electrochemical sensor based on bismuth molybdate/biochar (BMOC) electrode is proposed for Hg(II) detection. During the electrodeposition via the DPASV method, the massive electrons are generated by photoexcitation and the abundant active sites of BMOC contribute to the high accumulation of Hg(0), which can be thoroughly oxidized under the applied electrode potential. The synergistic effect caused by superoxide radicals and hydroxyl radicals generated during BMOC-assisted photocatalysis, greatly enhances the signal of the dissolution current and effectively eliminates the memory effect. The BMOC electrode benefits from these photoelectric properties and shows excellent measurement performance for Hg(II) over a wide range with a low detection limit of up to 3 × 10-5 µg·mL−1. Furthermore, the BMOC electrode exhibits a photoreduction efficiency of 99.99% for Cr(VI) (10 µg·mL−1) within 30 min under the visible light irradiation. The present study provides a viable photo-assisted sensing platform for efficient determination and reduction of HMIs.