Quantum Confinement and End-Sealing Effects for Highly Sensitive and Stable Nitrogen Dioxide Detection: Homogeneous Integration of Ti₃C₂T_<i>x</i>-Based Flexible Gas Sensors

The real-time and room-temperature detection of nitrogen dioxide (NO₂) holds significant importance for environmental monitoring. However, the performance of NO₂ sensors has been hampered by the trade-off between the high sensitivity and stability of conventional sensitive materials. Here, we present a novel fully flexible paper-based gas sensing structure by combining a homogeneous screen-printed titanium carbide (Ti₃C₂T_<i>x</i>) MXene-based nonmetallic electrode with a MoS₂ quantum dots/Ti₃C₂T_<i>x</i> (MoS₂ QDs/Ti₃C₂T_<i>x</i>) gas-sensing film. These precisely designed gas sensors demonstrate an improved response value (16.3% at 5 ppm) and a low theoretical detection limit of 12.1 ppb toward NO₂, which exhibit a remarkable 3.5-fold increase in sensitivity compared to conventional Au interdigital electrodes. The outstanding performance can be attributed to the integration of the quantum confinement effect of MoS₂ QDs and the conductivity of Ti₃C₂T_<i>x</i>, establishing the main active adsorption sites and enhanced charge transport pathways. Furthermore, an end-sealing effect strategy was applied to decorate the defect sites with naturally oxygen-rich tannic acid and conductive polymer, and the formed hydrogen bonding network at the interface effectively mitigated the oxidative degradation of the Ti₃C₂T_<i>x</i>-based gas sensors. The exceptional stability has been achieved with only a 1.8% decrease in response over 4 weeks. This work highlights the innovative design of high-performance gas sensing materials and homogeneous gas sensor techniques.