WO3/Bi2O2Se heterojunction nanocomposites for highly sensitive and selective NO2 detection

Tungsten oxide (WO 3 ) is widely used for detecting harmful gases, such as NO 2 , because of its excellent gas-sensing properties. However, pure WO 3 sensors suffer from high operating temperatures, poor selectivity, and rapid sensitivity degradation. In this study, for the first time, Bi 2 O 2 Se crystals were synthesized via a high-temperature solid-state reaction under a vacuum, and WO 3 /Bi 2 O 2 Se heterojunction composites were fabricated using a one-step hydrothermal method to enhance the NO 2 sensing performance. By adjusting the Bi 2 O 2 Se content, the optimal performance was achieved at 15 wt% Bi 2 O 2 Se (WB-15), which showed a high response (R g /R a = 3.42) toward 50 ppm NO 2 at 190 °C, a low detection limit (100 ppb), rapid response/recovery times (83/91 s), excellent repeatability (S = 2.42%), and good long-term stability. Characterization results showed that acidic etching (pH 1.7) increased the specific surface area and the number of active sites of Bi 2 O 2 Se, enhancing its gas adsorption capacity. Analysis of gas-sensing mechanism revealed that the n–n heterojunction between WO 3 and Bi 2 O 2 Se effectively modulated the interface barrier and carrier migration, intensifying the electron depletion effect under NO 2 and significantly improving the sensing response. This study introduced Bi 2 O 2 Se as a novel sensitizing material, offering a new approach for designing high-performance heterojunction gas sensors with enhanced sensitivity and selectivity.