Highly efficient synthesis of nitrogen-sulfur co-doped carbon dots from biomass waste and its application in the sensitive detection of methyl orange

In this paper, the hydrothermal carbon and thiourea were used as raw materials to develop a simple, economical and highly efficient synthesis route for nitrogen-sulfur co-doped carbon dots (HC-CDs). Among them, the hydrothermal carbon is obtained by the hydrothermal reaction of Chinese cabbage at 200 °C. The structure and optical properties of the synthesized HC-CDs were characterized by transmission electron microscopy, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and fluorescence spectroscopy. The obtained HC-CDs with a quantum yield of 55.6 % exhibit good solubility and stability in aqueous media, great resistance to photo-bleaching and stable fluorescence in the biological pH range. We found that methyl orange (MO) can effectively quench the fluorescence emission of HC-CDs, so HC-CDs are used as fluorescent probes for sensitive detection of MO. The limit of detection (LOD) is 0.92 μM, and the linear range is 0-100 μM. It proves the practicality and the possibility of large-scale production of converting biomass waste into carbon nanomaterials with great potential.