Composites were prepared from BiOI and Bi/BiOI-X (where x can be 1, 2, 3, or 4) by a one-step solvothermal method and used to design a photoelectrochemical (PEC) assay for chromium(VI). The chemical composition and morphology of the materials were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results of UV-vis DRS (Diffuse reflection spectra) and photoluminescence show the composites to have higher visible light absorption and a lower electron recombination rate compared to BiOI alone. Photogenerated electrons reduce hexavalent chromium to trivalent chromium, and the consumption of electrons cause noticeable enhances of the photocurrent density after the addition of Cr(VI). Thus, the Cr(VI) concentration can be measured by monitoring the increase of photocurrent density. The Bi/BiOI-3 material displays the best performance for detecting Cr(VI). The method has a wide linear range (1 to 230 μM) and a low detection limit of 0.3 μM (at S/N = 3). It is stable, selective, reproducible and was applied to the determination of nitrite in spiked tap water and lake water samples. Graphical abstract Schematic presentation of a electrochemical sensor based on Bi/BiOI for the determination of Cr(VI).
Keywords: Bi/BiOI; Chromate ion; Electron recombination rate; Hexavalent chromium; Photocurrent; Photoelectrochemical method; Photogenerated electrons; Solvothermal method; Trivalent chromium.