N, S-doped MXene quantum dots as novel fluorescent probes for wide range detection of Cr2O72−

Cr₂O₇ 2− is highly toxic and poses serious threats to ecosystems and human health, while its concentration in real water samples can vary widely depending on pollution sources and treatment processes, necessitating a wide-range detection method for both early warning at low concentrations and pollution assessment at high concentrations. Herein, N, S-doped MXene quantum dots (N, S-MQDs) were prepared under hydrothermal conditions using Ti 3 C 2 nanosheets as the precursor and thiourea as the dopant, and were employed as fluorescent probes for the detection of Cr 2 O 7 2− . Strong fluorescence emission at 435 nm was detected for N, S-MQDs under the optimal excitation wavelength of 350 nm. After Cr 2 O 7 2− was added, the emission intensity of N, S-MQDs gradually decreased. N, S-MQDs exhibited a wide detection range of 3–550 μM for Cr 2 O 7 2− , and the detection limit was determined as 1.68 μM. Mechanistic analysis indicated that the fluorescence attenuation was predominantly induced by inner filter effect. These results demonstrate that N, S-MQDs are promising fluorescent probes for wide-range and highly selective detection of Cr 2 O 7 2− .