Covalently N-Doped MXene Quantum Dots for Highly Stable Fluorescent Cu²⁺ Ion Sensor

MXene quantum dots (MQDs) have excellent photoelectrochemical properties and are attracting considerable attention in the academic field. In this study, we synthesized amino-rich MQDs on the surface by modifying the Ti3C2 nanosheets with 3-aminopropyltriethoxysilane (APTES) and then cutting the functional nanosheets into quantum dots by hydrothermal reaction. The N-MQDs were characterized by UV–vis spectrophotometry, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The prepared N-MQDs had an average particle size of 8.63 nm. The N-MQDs exhibited excellent linearity and sensitivity for the detection of Fe3+ and Cu2+ ions over a concentration range of 0.5–500 μM. The limits of detection (LODs) for the Fe3+ and Cu2+ ions were calculated to be 0.17 and 0.15 μM, respectively. Compared with previous N-doped Ti3C2 MQDs, our prepared N-MQDs possessed lower LOD for the detection of Cu2+ ions. The quantum dot showed a potential to detect Cu2+ ions in water samples with sodium hexametaphosphate (SHPP) as a Fe3+ions masking agent. N-doped MQDs can enhance the fluorescence quantum yield and detection sensitivity for metal ions over that of MQDs without amination. N-MQDs prepared by the method with active amino groups and high stability than previous works, which can expand the application of MQDs in other fields. This study also opens an avenue for the covalent modification of MXene QDs materials and surface engineering fields.