Herein, by using the green and cheap L-cysteine as the precursor, nitrogen and sulfur codoped carbon dots (NS-CDs) were synthesized via a facile one-step hydrothermal method. The obtained NS-CDs showed the relatively narrow size distributions (2.1~3.9 nm) with the lattice spacing of 0.29 nm, as well as the excitation-dependent photoluminescence (PL) emission activity with the quantum yield (QY) of 18%. More interestingly, the PL intensity of NS-CDs was quenched by the addition of copper or lead ions (Cu²⁺ or Pb²⁺), which was shown in the tradition detection method by PL spectra. The NS-CDs exhibited ultrasensitive colorimetric sensing capability for both Cu²⁺ and Pb²⁺ by the color variance using naked eyes without any further treating. Two different coupling ways for detecting Pb²⁺ and Cu²⁺ were induced by the analysis of the Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). And the as-prepared NS-CDs showed their potential application in the heavy metal ions detection for the wastewater determination.

中文翻译：

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一步法合成氮和硫共掺杂碳点用于检测水溶液中的铅和铜离子

在此，以绿色廉价的L-半胱氨酸为前体，通过简便的一步水热法合成了氮和硫共掺杂碳点（NS-CD）。所获得的NS-CD具有相对窄的尺寸分布（2.1〜3.9 nm），晶格间距为0.29 nm，以及激发依赖性光致发光（PL）发射活性，量子产率（QY）为18％。更有趣的是，NS-CDs的PL强度通过添加铜或铅离子（Cu ²⁺或Pb ²⁺）淬灭，这在传统检测方法中通过PL光谱显示。NS-CD对Cu ²⁺和Pb ²⁺均表现出超灵敏的比色传感能力通过使用裸眼的颜色变化无需任何进一步处理。通过傅里叶变换红外光谱（FT-IR）和X射线光电子能谱（XPS）的分析，得出了两种不同的检测Pb ²⁺和Cu ^2+的耦合方式。制备的NS-CDs在重金属离子检测中具有潜在的应用价值。