Green synthetic carbon quantum dots based on waste tobacco leaves and its application to detecting borax content in flour and its products

In this study, carbon quantum dots (CQDs) were prepared using discarded tobacco leaves as the precursor material combined. And the method used in our experiment is a green, low-cost, and simple one-step hydrothermal method. The structural morphology, optical properties, and fundamental elemental composition of these CQDs were characterized via transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectrum (XRD), etc. A fluorescence probe was developed with these CQDs for borax determination. Influencing factors including solution salt concentration, interfering substances, and solution pH on the detection of borax were investigated. The fluorescence enhancement degree of these CQDs had a linear relationship with different concentrations of borax (0.025–5 mmol·L-1), r2 = 0.9961, and based on the formula 3σ/S, σ represents the standard deviation of the detection data for 11 blank samples, S refers to the slope of the standard curve, LOD = 8.0 µmol·L-1. Furthermore, we also initially elucidated the fluorescence enhancement mechanism of CQDs. Satisfactory results were obtained for borax determination in flour, bread, and instant noodle samples.