Metal-free carbon quantum dots (CQDs) have attracted great interest, but the rapid preparation of doped
CQDs with tunable optical properties is still an urgent task. Herein, we report that covalent organic
frameworks (covalent triazine-based frameworks, CTF-1) with layered structures can be rapidly exfoliated
and cut into N-doped CQDs. The cutting mechanism involves triazine hydrolysis and breaking the bonds
between the triazines and benzene rings. Experiments and density functional theory (DFT) calculations
confirm that the fluorescence of the obtained CQDs mainly originates from the intrinsic state emission
induced by localized p–p* transitions, despite the contribution of the defect state emission. Due to their
unique chemical structure, the CQDs could be further utilized as an efficient PL probe for detecting
Hg2+. This study may open up new avenues for developing new kinds of CQDs using covalent organic
frameworks as the starting materials.