Ultrasensitive NO₂ Detection Utilizing Mesoporous ZnSe/ZnO Heterojunction-Based Chemiresistive-Type Sensors

Mesoporous ZnSe/ZnO heterojunctions were prepared by the in situ thermal oxidation of ZnSe at elevated temperatures in air. The partial replacement of selenium by oxygen in the ZnSe nanoflakes led to a highly porous microstructure with 8.2 nm mesopores distributed fairly uniformly within the formed heterojunction sample. The as-fabricated mesoporous ZnSe/ZnO heterojunction-based sensor exhibits an approximately 7.3-fold significantly higher response than those of both pristine ZnO- and ZnSe-based sensors when exposed to 8 ppm NO₂ at 200 °C. This sensor also demonstrates excellent selectivity for methanol, ethanol, acetone, benzene, methylbenzene, ammonia, and formaldehyde. The significantly enhanced response of the ZnSe/ZnO-based sensor is due to the mesoporous microstructure during thermal oxidation of ZnSe to ZnO, yielding more active sites and the accumulation of electrons in the ZnO nanocrystals transferred between ZnSe/ZnO interfaces.