p–p Heterojunction Sensors ofp-Cu3Mo2O9Micro/Nanorods Vertically Grown onp-CuO Layers for Room-Temperature Ultrasensitive and Fast Recoverable Detection of NO2

High sensitivity, low limit of detection (LOD), and short response and recovery times at room temperature (RT) are critical for gas sensors. For NO 2, different binary metal oxide-based sensors were developed to achieve superior performance at elevated temperatures instead of RT. Herein, we report on CuO@CuO and Cu 3 Mo 2 O 9 @CuO sensors with CuO and Cu 3 Mo 2 O 9 micro/nanorods vertically aligned on the CuO layers, which were directly fabricated using a facile, low-cost, and catalyst-free chemical vapor deposition (CVD) technique. Their sensing performance tests revealed that the Cu 3 Mo 2 O 9 @CuO p–p heterojunction sensors exhibited a high response of 160% to 5 ppm NO 2, an excellent sensitivity of 50% ppm –1, a low LOD of 2.30 ppb, a short response time of 49 s, and a rapid recovery of 241 s at RT, obviously better than those for CuO@CuO sensors. The superior performance of Cu 3 Mo 2 O 9 @CuO sensors could be attributed to the Schottky heterojunction formed between p -Cu 3 Mo 2 O 9 micro/nanorods and p -CuO films, the catalytic effect, and the anisotropic nature of Cu 3 Mo 2 O 9 micro/nanorods. This study not only provides a simple, low-cost, and batchable fabrication method of homo/heterojunction sensors with micro/nanorods vertically aligned on films but also opens an avenue for sensor design by tuning the Schottky barrier height to enhance RT performance.