Highly Selective Room Temperature Detection of NH3 and NOx Using Oxygen-Deficient W18O49-Supported WS2 Heterojunctions

In this paper, we reported the controlled synthesis of tungsten disulfide/reduced tungsten oxide (WS 2 /W 18 O 49 ) heterojunctions for highly efficient room temperature NO x and ammonia (NH 3 ) sensors. X-ray diffraction analysis revealed the formation of the oxygen-deficient W 18 O 49 phase along with WS 2 . Field-emission scanning electron microscopy and transmission electron microscopy displayed the formation of WS 2 flakes over W 18 O 49 nanorods. X-ray photoelectron spectroscopy showed the presence of tungsten in W 4+, W 5+, and W 6+ oxidation states corresponding to WS 2 and W 18 O 49, respectively. The WS 2 /W 18 O 49 heterojunction sensor exhibited sub-ppm level sensitivity to NO x and NH 3 at room temperature. The heterojunction sensor detected 0.6 ppm NO x and 0.5 ppm NH 3, with a corresponding response of 7.1 and 3.8%, respectively. The limit of detection of the sensor was calculated to be 0.05 and 0.17 ppm for NH 3 and NO x, respectively. The cyclic stability test showed that the sensor exhibited high stability even after 24 cycles for the detection of NH 3 and 14 cycles for NO x . Compared to pristine WO 3 and WS 2, the WS 2 /W 18 O 49 heterojunction showed high selectivity toward NO x and NH 3 . The results could be useful for the development of room temperature NO x and NH 3 sensors.