## 4 Conclusions  
In conclusion, CBs/g-C\({}_{3}\)N\({}_{4}\) composites were synthesized and innovatively applied as SPME coatings for the sensitive determination of eight CBs from water coupled to GC-MS. The doping of CDs improved the extraction efficiency, owing to their abundant chemical groups, and enabled CDs/g-C\({}_{3}\)N\({}_{4}\) composites exhibit superior extraction efficiency in comparison to commercial coatings. The proposed method presented extremely low LODs, ranging from 0.002 to 0.086 ng L\({}^{-1}\) for CBs, which is better than the methods reported in the literature. Finally, the proposed method was used for the analysis of real river waters successfully. Outstanding properties, such as high sensitivity and excellent reproducibility, gives the proposed method great potential for the analysis of trace pollutants from aqueous samples.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/nano12030335/s1](https://www.mdpi.com/article/10.3390/nano12030335/s1)]([https://www.mdpi.com/article/10.3390/nano12030335/s1](https://www.mdpi.com/article/10.3390/nano12030335/s1)), Section S1: Operating parameters of GC-MS; Table S1: Retention time and characteristic ions of eight CBs; Table S2: BET and BJH results of as-prepared materials; Figure S1: Reusability of as-prepared SPME fiber.  
**Author Contributions:** S.X.: conceptualization, methodology, and writing--original draft preparation; H.L. ([PERSON]): investigation and validation; A.L.: resources; H.L. ([PERSON]): formal analysis; C.C.: writing--review and editing; S.F.: supervision; J.F.: project administration. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was financially supported by funding from the National Natural Science Foundation of China (21976052, 21777038, 21977025), the Natural Science Foundation of Guizhou Province of China ([2019]1423), the Youth Science Foundation of Henan Normal University (20200183), and Henan Special Support for High-level Talents, Central Plains Science, and Technology Innovation Leading Talents (204200510006).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** This study presents novel concepts and did not report any data.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **Analytes** & **135-TCB** & **124-TCB** & **123-TCB** & **1245-TeCB** & **1234-TeCB** & **PeCB** & **HeCB** & **PeCNB** \\ \hline \multirow{4}{*}{1\#} & Found (ng L\({}^{-1}\)) & ND & ND & 1.7 & ND & ND & ND & ND \\  & RSDs (\%, \(n=3\)) & - & - & 0.8 & - & - & - & - \\  & Recoveries & & & & & & & \\  & (\%, spiked with & 105.1 & 75.5 & 88.8 & 94.5 & 93.8 & 80.3 & 101.1 & 83.4 \\  & 1 ng L\({}^{-1}\)) & & & & & & & & \\  & Found (ng L\({}^{-1}\)) & 154.0 & ND & 11.7 & ND & ND & ND & 57.6 & ND \\
2\# & RSDs (\%, \(n=3\)) & 11.4 & - & 13.9 & - & - & - & 20.6 & - \\  & Recoveries & & & & & & & & \\  & (\%, spiked with & 108.5 & 105.5 & 109.1 & 84.4 & 84.2 & 122.3 & 93.5 & 75.5 \\  & 10 ng L\({}^{-1}\)) & & & & & & & & \\  & Found (ng L\({}^{-1}\)) & 60.4 & ND & 6.4 & ND & ND & ND & ND & ND \\
3\# & RSDs (\%, \(n=3\)) & 9.9 & - & 24.6 & - & - & - & - & - \\  & Recoveries & & & & & & & \\  & (\%, spiked with & 90.8 & 81.9 & 83.4 & 83.1 & 73.4 & 76.8 & 81.2 & 81.8 \\  & 10 ng L\({}^{-1}\)) & & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Analytical results and recoveries for the determination of CBs in real water samples.  
**Acknowledgments:** The authors would like to thank [PERSON] and [PERSON] from Shiyanjia Lab (www.shiyanjia.com accessed on 18 January 2022) for the TEM and BET analysis.  
**Conflicts of Interest:** The authors declare no conflict of interest.