TiO ₂ /SnO ₂ −Pt Janus-Type Nanofibers with Gradient Band Distribution for Enhanced Room-Temperature NO ₂ Detection via Cascade Photo-Generated Charge Transfer

Room-temperature metal oxide semiconductor (MOS) gas sensors enabled by photoexcitation have demonstrated significant potential in various applications due to their outstanding advantages, such as the absence of heating requirements, low power consumption, and high safety. However, conventional MOS often suffers from inefficient charge separation and rapid recombination of photogenerated carriers, which significantly hamper the sensing performance of photoexcited MOS gas sensors. Here, we designed ternary TiO 2 /SnO 2 −Pt Janus-type heterojunction nanofibers (JHNFs) with a gradient band distribution for high-performance NO 2 detection. The structurally ordered, one-dimensional nanofiber architecture largely promotes efficient and directional transport of photogenerated carriers. The gradient band distribution of the TiO 2 /SnO 2 −Pt JHNFs facilitates a cascade charge transfer pathway, synergistically enhancing photogenerated carrier utilization and surface NO 2 adsorption. Under room-temperature UV excitation, the sensors based on TiO 2 /SnO 2 −Pt JHNFs demonstrate a much higher response to NO 2 compared to pure SnO 2 (5.3-fold enhancement) and TiO 2 (6.7-fold enhancement) counterparts. In addition, the sensor achieves a low detection limit of 50 ppb, rapid response/recovery, and excellent long-term stability. Our findings not only systematically unravel the relationship between gas sensing performance and photogenerated carrier separation but also establish a feasible design strategy for developing high-performance photoactivated room-temperature gas sensors.