Fast and recoverable NO2 detection achieved by assembling ZnO on Ti3C2Tx MXene nanosheets under UV illumination at room temperature

Recently, Ti3C2Tx MXenes have begun to receive attention in the field of gas sensors owing to their characteristics of high conductivity and abundant surface functional groups. However, Ti3C2Tx-based gas sensors still suffer from the drawbacks of low sensitivity and sluggish response/recovery speed towards target gases, limiting their development in further applications. In this work, Ti3C2Tx-ZnO nanosheet hybrids were fabricated through a simple sonication method. The Ti3C2Tx-ZnO nanosheet hybrids exhibited a short recovery time (10 s) under UV (ultraviolet) illumination, a short response time (22 s), a high sensitivity (367.63% to 20 ppm NO2) and selectivity. Furthermore, the Ti3C2Tx-ZnO sensor has prominent anti-humidity properties, as well as superior reproducibility in multiple tests. The abundant active sites in the Ti3C2Tx-ZnO nanosheet hybrids, including surface groups (-F, -OH, -O) of Ti3C2Tx and oxygen vacancies of ZnO, the formation of Schottky barriers between Ti3C2Tx and ZnO nanosheets and the rich photogenerated charge carriers of ZnO under UV illumination, together result in excellent gas-sensing performance. Density functional theory calculations have been further employed to explore the sensing performance of Ti3C2Tx and ZnO nanosheets, showing strong interactions existing between the NO2 and ZnO nanosheets. The main adsorption sites for NO2 were present on the ZnO nanosheets, while the Ti3C2Tx played the role of the conductive path to accelerate the transformation of charge carriers. Our work can provide an effective way for improving the gas-sensing performances of Ti3C2Tx-based gas sensors.