Background: Dichromate (Cr2O7 2-) ion is one of the carcinogenic and toxic spices in environment which can easily contaminate the environment due to its high solubility in water. Therefore, a lot of attention has been focused on the detection of Cr2O7 2- with high sensitivity and selectivity.

Methods: In present work, nitrogen-rich precursor was used for synthesizing graphitic carbon nitride (g-C3N4) nanostructures through hydrothermal oxidation of g-C3N4 nanosheets. The prepared nanostructures show two distinct fluorescence emissions centered at 368 and 450 nm which are highly sensitive toward Cr2O7 2- ions.

Results: The as-prepared g-C3N4 was characterized by several techniques such as Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and fluorescence emission spectra. The XRD pattern of prepared nanostructures illustrated two diffraction patterns (at 13.4° and 27.6°) indicating tri-s-tri-azine-based structures. The g-C3N4 exhibited good selectivity and sensitivity toward Cr2O7 2- among other anions. According to titration test, the detection limit and stern-volmer constant (Ksv) were calculated as 40 nM and 0.13×106 M-1, respectively. The investigation of quenching mechanism shows that Cr2O7 2- may form hydrogen bonding with surface groups of g-C3N4 (such as NH2, OH and COOH) resulted in more fluorescence quenching in comparison with the pure inner filter effect.

Conclusion: The g-C3N4 nanostructures were successfully synthesized through the hydrothermal oxidation. The as-prepared g-C3N4 can be used as a highly sensitive fluorescent probe for the selective determination of Cr2O7 2 ion among other anions. The quenching mechanism was experimentally studied. According to reliable responses in real sample tests, it can be proposed that g-C3N4 nanostructure is a suitable sensitive nanosensor for detection of Cr2O7 2 ions in aqueous media.

背景：重铬酸根（Cr2O7 2-）离子是环境中的一种致癌和有毒的香料，由于其在水中的高度溶解性，很容易污染环境。因此，在高灵敏度和高选择性的Cr 2 O 7 2-的检测上已经引起了很多关注。

方法：在目前的工作中，使用富氮前体通过水热氧化g-C3N4纳米片来合成石墨氮化碳（g-C3N4）纳米结构。制备的纳米结构显示出两个分别在368和450 nm处集中的荧光发射，这些荧光发射对Cr2O7 2-离子高度敏感。

结果：制备的g-C3N4通过几种技术进行了表征，例如傅立叶变换红外光谱（FTIR），扫描电子显微镜（SEM），X射线衍射（XRD）和荧光发射光谱。制备的纳米结构的XRD图谱显示了两个衍射图谱（在13.4°和27.6°），表明基于三-s-三嗪的结构。除其他阴离子外，g-C3N4对Cr2O7 2-表现出良好的选择性和敏感性。根据滴定测试，检出限为40 nM，船尾体积常数（Ksv）为0.13×106 M-1。猝灭机理的研究表明，与纯内部滤光效果相比，Cr2O7 2-可能与g-C3N4的表面基团（如NH2，OH和COOH）形成氢键，从而导致更多的荧光猝灭。

结论：通过水热氧化成功地合成了g-C3N4纳米结构。所制备的g-C3N4可用作高灵敏度的荧光探针，用于选择性测定Cr2O7 2离子以及其他阴离子。实验研究了淬灭机理。根据实际样品测试中的可靠响应，可以提出g-C3N4纳米结构是用于检测水性介质中Cr2O7 2离子的合适灵敏纳米传感器。