Heteroatom-doped MXene quantum dots: red emission tuning and dual-functional performance.

BACKGROUND: TiCT MXene-derived quantum dots (MQDs) have attracted increasing interest due to their tunable photoluminescence and abundant surface-active sites, enabling applications in optical sensing and photocatalysis. Modulating the emission wavelength and improving light-harvesting efficiency remain central challenges for expanding their functionality under visible-light conditions. Heteroatom doping offers a promising route to engineer the electronic structure and emission behavior of MQDs. Nevertheless, a systematic strategy to simultaneously achieve long-wavelength emission, high quantum efficiency, and multifunctional performance in MXene quantum dots remains insufficiently developed. RESULTS: Nitrogen and sulfur co-doped MXene quantum dots (N,S-MQDs) with distinct red emission were synthesized via a facile hydrothermal approach. Co-doping induced a pronounced photoluminescence shift from green to red, accompanied by a significant increase in quantum yield from 5.26% to 13.12%. Particle size analysis revealed an enlarged average size after doping, contributing to emission red-shifting through relaxation of the quantum confinement effect. The red-emitting N,S-MQDs functioned as highly sensitive fluorescent probes for crystal violet (CV), achieving an ultralow detection limit of 0.01 nM via an internal filtration effect-dominated mechanism. In addition, the same material exhibited excellent visible-light-driven photocatalytic activity toward CV degradation, reaching efficiencies up to 98%. The broadened visible-light response enhanced photon utilization and photoinduced charge-transfer efficiency. SIGNIFICANCE: This work demonstrates heteroatom co-doping as an effective and versatile strategy to synergistically regulate emission wavelength, quantum efficiency, and redox activity in MXene quantum dots. The integration of ultrasensitive fluorescence sensing and efficient visible-light photocatalysis within a single red-emitting MQD platform provides a rational design paradigm for multifunctional nanomaterials in environmental monitoring and solar-driven remediation.