Enhanced room-temperature NO2 sensing performance of SnO2/Ti3C2 composite with double heterojunctions by controlling co-exposed {221} and {110} facets of SnO2

Here, we firstly synthesized SnO2/Ti3C2 composites with Schottky and surface heterojunctions via a hydrothermal oxidation process to lower the operation temperature of SnO2-based gas sensors and increase the response of Ti3C2-based gas sensors simultaneously. The SnO2 nanoparticles are mainly surrounded by {221} and {110} facets by controlling the HCl content, and a surface heterojunction is formed inside SnO2 due to the difference in energy band structure between {221} and {110} facets. The synergistic effect of the SnO2/Ti3C2 Schottky heterojunction and SnO2 {221}/{110} surface heterojunction can accelerate electron transport and thus enhance sensitivity to NO2. Under a moderate pulse heating (100 °C) during desorption process, the optimal SnO2/Ti3C2 composite presents the outstanding responses (ΔR/Ra) of 0.02, 0.83 and 1.57 to 0.05, 5 and 10 ppm NO2 at room temperature, respectively. Moreover, the optimal SnO2/Ti3C2 composite exhibits the excellent linear response (R2 = 0.99729) and good recycling performance and selectivity to NO2. This work provides an idea for synergistically improving the gas-sensing performance of MXene by in-situ constructing double heterojunctions.