Ultra-sensitive trace NO2 detection based on quantum dots-sensitized few-layer MXene: A novel convincing insight into dynamic gas-sensing mechanism

It is critical for MXene to overcome the constraints of weak gas adsorption capacity, poor sensitivity and limited selectivity properties. Herein, quantum dots (QDs)-sensitized few-layer Ti3C2Tx was successfully constructed for efficient NO2-sensing. The ideal doping content was investigated according to multiple structural analysis and sensing-properties. Impressively, the FLTS-2 sensor displays a significant 42.05-fold response (60.38%, 500-ppb NO2) compare to pure MXene (1.43%). It also exhibits ideal selectivity, well long-term stability and lower detection limit (0.83-ppb), demonstrating its considerable potential for trace-level monitoring and practical applications. Meanwhile, a novel convincing dynamic gas-sensing mechanism is proposed to elucidate the enhancement of sensing-capabilities, including gas diffusion/adsorption, selective mechanisms, DFT calculations (37 models, 100 images) and QDs-sensitization mechanisms. Strikingly, dynamic gas-sensing mechanism proves that the surface functionalization of QDs modifications strongly improves the adsorption behavior and significantly facilitates the electron transfer of NO2 molecules, thus enhancing the sensing performance. The present experiment and mechanism analysis not only highlight the promising combination of 2D/0D MXene/PbS heterostructures, but also provide a theoretical perspective for designing of MXene-based sensors for trace NO2 detection.