Sensitive and selective detection of chromium (VI) via static quenching using a graphene quantum dots/bismuth oxybromide/graphitic carbon nitride (GQDs/BiOBr/g-C3N4) fluorescent probe

Hexavalent chromium (Cr(VI)) poses considerable environmental and health hazards owing to its high solubility and mobility. Therefore, developing highly sensitive detection methods for Cr(VI) is essential. In this work, a multifunctional graphene quantum dots/bismuth oxybromide/graphitic carbon nitride (GQDs/BiOBr/g-C 3 N 4 ) fluorescent probe with excellent detection and removal capabilities was synthesized through integrated hydrothermal treatment, calcination, and coprecipitation. Optimization studies showed that maximum sensitivity was achieved at pH 7.5, a probe concentration of 2.5 mg/L, and a reaction time of 20 min. Cr(VI) induced selective fluorescence quenching at 436 nm, displaying a linear response (R 2 = 0.966) over the range of 0–200 μmol/L, with a detection limit of 24.84 μmol/L. The probe maintained > 90 % fluorescence stability under UV irradiation (365 nm, 180 min), high ionic strength (0.1 mol/L NaCl), and in the presence of various interferents (10 common metal ions and non-fluorescent dyes). Analysis of the nonlinear Stern–Volmer plot, EDTA-2Na-mediated fluorescence recovery, and lifetime measurements suggests a static quenching mechanism, in which the excited-state electrons of GQDs/BiOBr/g-C 3 N 4 interact with Cr(VI), driving a nonradiative complexation process. This study demonstrates a dual-functional material capable of simultaneous Cr(VI) detection and removal, providing a practical platform for environmental monitoring.