Facile fabrication of nanoflower-like WO/WS heterojunction for highly sensitive NO detection at room temperature.

Realizing efficient detection of ultra-low concentrations of hazardous gases contributes to air pollution monitoring, ecosystem and human health protection. Herein, we firstly fabricated the nanoflower-like WO/WS composites by a facile process to highly sensitively detect NO at room temperature. The WO content in the WO/WS composites can be adjusted by altering the calcination temperature, and the WO nanoparticles disperse uniformly on the WS surface, forming the WO/WS heterojunction. The room-temperature responses of WO/WS composites gradually climb with the NO concentration increasing from 0.005 to 5 ppm, and the WW-280 and WW-300 composites possess the optimal gas sensitivity when the NO concentrations are lower and higher than 100 ppb, respectively. In particular, the two WO/WS composites present the limitation of detection (LOD) of ≤ 5 ppb, and they exhibit the excellent selectivity, good reproducibility and long-term stability towards NO. A possible gas sensing mechanism was also proposed from the point of views of gas adsorption, redox reactions and electron transfer. The appropriate WO content and molar ratio of hexagonal to monoclinic WO, and the formation of WO/WS p-n heterojunction can contribute to the high sensitivity of WO/WS composite to various concentrations of NO. This work offers a promising gas sensing material for room-temperature detection to low concentrations of NO.