Highly sensitive NO2 sensor based on square-like tungsten oxide prepared with hydrothermal treatment

The square-like WO3 nanosheets were synthesized by hydrothermal treatment of irregular WO3 nanosheets prepared through acidification of Na2WO4·2H2O. The obtained square-like and irregular WO3 nanosheets were characterized with field emission scanning electron microscopy, X-ray powder diffraction and transmission electron microscopy. The gas sensing properties of sensors based on as-prepared samples were investigated. The results indicated that both samples exhibited high response to NO2. The sensor based on square-like WO3 nanosheets exhibited remarkably enhanced response and faster response/recovery time for NO2 compared with that based on irregular nanosheets. Especially, the sensor based on square-like WO3 nanosheets could detect NO2 down to 40 ppb, which covered environmental standard. A possible reason for the influence of unique structure on the sensing properties of sensors based on square-like WO3 was proposed.