Highly sensitive detection of chromium (VI) by photoelectrochemical sensor based on p-n heterojunction of carbon nitride-modified BiOI

Highlights: • A p-n heterojunction BiOI/CN was successfully prepared by combining petal-like CN with BiOI. • BiOI/CN-34% shows the best PEC performance under visible light. • The PEC sensor based on BiOI/CN-34% could be used to detect Cr (VI) with a wider linear range from 0.5 µM to 190 µM. • The prepared PEC sensor could detect real samples with excellent sensitivity, good stability and reproducibility. -- Abstract: In this study, bismuth oxyiodide (BiOI) was synthesized by one-step solvothermal method firstly. Then it was combined with different mass ratio of carbon nitride (CN) to obtain the BiOI/CN-X (X is the mass ratio of CN to BiOI, X = 11%, 34%, 56%). The chemical composition and morphology of these samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Furthermore, through the photoelectrochemical (PEC) measurements, UV-Visible diffuse reflectance spectra (UV-Vis DRS) and photoluminescence (PL) spectra confirmed that the synthesized materials (BiOI/CN-34%) exhibit the highest PEC activity, wider visible light absorption range and increased carrier lifetime. Subsequently, the PEC sensor based on BiOI/CN-34% was designed to detect hexavalent chromium (Cr (VI)) under visible light irradiation. The prepared sensor shows a lower detection limit of 0.1 µM (the signal to noise ratio (S/N = 3)), with a wider linear range from 0.5 µM to 190 µM. Meanwhile, the PEC sensor of BiOI/CN-34% can be applied to the real sample detection with good stability, reproducibility, and selectivity. Thus, BiOI/CN-34% has potential application in Cr (VI) detection.