Fluorescence quenching of carbon dots (CDs) has been widely used for ions detection, but it usually exhibits poor selectivity for specific ions, so how to enhance their response selectivity is still an urgent task. In this paper, CDs and carbon nitride (C₃N₄) nanosheets are prepared by pyrolysis and thermal oxidation method, respectively, followed by their ultrasonic mixing to synthesize CDs/C₃N₄ composites. They are characterized by transmission electron microscope, X-ray diffractometer, X-ray photoelectron spectrometer, Fourier transform infrared spectroscopy, UV–vis and fluorescence spectrophotometer. The synthesized CDs and C₃N₄ nanosheets both exhibit strong fluorescence response to multiple ions. As a comparison, CDs/C₃N₄ composites exhibit highly enhanced selectivity to Cr⁶⁺ as a result of partial consumption of -NH₂ groups and CN bonds or their reduced binding ability. Meanwhile, our CDs/C₃N₄ probe exhibits high sensitivity of 54 %, short response time of less than 1 min, low detection limit of 0.39 μM, wide linear response interval of 2.0−80.0 μM and high stability.

碳点（CDs）的荧光猝灭已广泛用于离子检测，但通常对特定离子的选择性较差，因此如何提高其响应选择性仍然是紧迫的任务。本文分别通过热解和热氧化方法制备了CDs和氮化碳（C ₃ N ₄）纳米片，然后对其进行超声混合以合成CDs / C ₃ N ₄复合材料。它们的特征在于透射电子显微镜，X射线衍射仪，X射线光电子能谱仪，傅立叶变换红外光谱仪，紫外可见光谱仪和荧光分光光度计。合成的CD和C ₃ N ₄纳米片均显示出对多种离子的强烈荧光响应。作为比较，由于-NH ₂基团和C N键的部分消耗或它们降低的结合能力，CDs / C ₃ N ₄复合材料表现出对Cr ^6+的高度选择性。同时，我们的CDs / C ₃ N ₄探针具有54％的高灵敏度，不到1分钟的短响应时间，0.39μM的低检测限，2.0−80.0μM的宽线性响应区间和高稳定性。