Synthesis of durian shell-based carbon dots and its application in the detection of $${\text{MnO}}_{4}^{ - }$$ and $${\text{Cr}}_{{2}} {\text{O}}_{7}^{2 - }$$

Using durian shell as a carbon source and triethanolamine as a nitrogen dopant, nitrogen-doped carbon dots (N-CDs) were prepared via the hydrothermal method. First, by exploring different reaction times, reaction temperatures, and carbon source/dopant ratios to synthesize nitrogen-doped carbon dots, it is concluded that the best process conditions are 200 ℃, reaction time being 15h, and the dopant addition amount being 2mL. Structure and characteristics of the synthesized CDs were analyzed using X-ray photoelectron spectroscopy, Fourier-transform infrared, fluorescence (FL), ultraviolet–visible absorption, and Raman spectra. The N-CDs showed blue FL with a quantum efficiency of 4.28%. The FL characteristics of the N-CDs were utilized for ion detection, which demonstrated that \({\text{MnO}}_{4}^{ - }\) and \({\text{Cr}}_{{2}} {\text{O}}_{7}^{2 - }\) ions caused distinct FL quenching through static quenching, while other ions had no significant quenching effect. The detection limits for \({\text{MnO}}_{4}^{ - }\) and \({\text{Cr}}_{{2}} {\text{O}}_{7}^{2 - }\) were 37.5 and 46.2 nM, respectively. The N-CDs were subsequently employed to detect these ions in actual water samples, producing satisfactory results. Therefore, the preparation of N-CDs using durian shell as raw material and its application in practical detection work have good application feedback, which not only provides a new way for the reuse of fruit and vegetable wastes but also provides a new detection means for environmental monitoring pollutants.