Quantum Confinement\nand End-Sealing Effects for Highly\nSensitive and Stable Nitrogen Dioxide Detection: Homogeneous Integration\nof Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub>‑Based\nFlexible Gas

The\nreal-time and room-temperature detection of nitrogen dioxide\n(NO<sub>2</sub>) holds significant importance for environmental monitoring.\nHowever, the performance of NO<sub>2</sub> sensors has been hampered\nby the trade-off between the high sensitivity and stability of conventional\nsensitive materials. Here, we present a novel fully flexible paper-based\ngas sensing structure by combining a homogeneous screen-printed titanium\ncarbide (Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub>) MXene-based nonmetallic electrode with a MoS<sub>2</sub> quantum\ndots/Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> (MoS<sub>2</sub> QDs/Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub>) gas-sensing film. These precisely designed gas sensors demonstrate\nan improved response value (16.3% at 5 ppm) and a low theoretical\ndetection limit of 12.1 ppb toward NO<sub>2</sub>, which exhibit a\nremarkable 3.5-fold increase in sensitivity compared to conventional\nAu interdigital electrodes. The outstanding performance can be attributed\nto the integration of the quantum confinement effect of MoS<sub>2</sub> QDs and the conductivity of Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub>, establishing the main active adsorption sites and\nenhanced charge transport pathways. Furthermore, an end-sealing effect\nstrategy was applied to decorate the defect sites with naturally oxygen-rich\ntannic acid and conductive polymer, and the formed hydrogen bonding\nnetwork at the interface effectively mitigated the oxidative degradation\nof the Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub>-based\ngas sensors. The exceptional stability has been achieved with only\na 1.8% decrease in response over 4 weeks. This work highlights the\ninnovative design of high-performance gas sensing materials and homogeneous\ngas sensor techniques.