Electronic sensitization enhanced p-type ammonia gas sensing of zinc doped MoS2/RGO composites.

Zinc (Zn) doping induced synergetic effects of defects engineering and heterojunction in Molybdenum disulphide/Reduced graphene oxide (MoS2/RGO) effectively enhances the p-type Volatile organic compounds (VOC) gas sensing traits and helps in tailoring the over dependence on noble metals for surface sensitization. Through this work, we have successfully prepared Zn doped MoS2 grafted on RGO employing an in-situ hydrothermal method. Optimal doping concentration of Zn dopants in the MoS2 lattice triggered more active sites on the basal plane of MoS2 with the aid of defects promoted by the zinc dopants. Effective intercalation of RGO further boost up the exposed surface area of Zn doped MoS2 for further interaction of ammonia gas molecules. Besides, smaller crystallite size brought out by 5% Zn dopants aids in efficient charge transfer across the heterojunctions that further amplifies the ammonia sensing traits with a peak response of 32.40% along with a response time of 21.3 s and recovery time of 44.90 s. The as prepared ammonia gas sensor exhibited excellent selectivity and repeatability. The obtained results reveal that transition metal doping into the host lattice proves to be a promising approach for VOC sensing characteristics of p-type gas sensors and gives insight about the importance of dopants and defects for the development of highly efficient gas sensors in the future.

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 (WS2/W18O49) heterojunctions for highly efficient room temperature NOx and ammonia (NH3) sensors. X-ray diffraction analysis revealed the formation of the oxygen-deficient W18O49 phase along with WS2. Field-emission scanning electron microscopy and transmission electron microscopy displayed the formation of WS2 flakes over W18O49 nanorods. X-ray photoelectron spectroscopy showed the presence of tungsten in W4+, W5+, and W6+ oxidation states corresponding to WS2 and W18O49, respectively. The WS2/W18O49 heterojunction sensor exhibited sub-ppm level sensitivity to NOx and NH3 at room temperature. The heterojunction sensor detected 0.6 ppm NOx and 0.5 ppm NH3, 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 NH3 and NOx, respectively. The cyclic stability test showed that the sensor exhibited high stability even after 24 cycles for the detection of NH3 and 14 cycles for NOx. Compared to pristine WO3 and WS2, the WS2/W18O49 heterojunction showed high selectivity toward NOx and NH3. The results could be useful for the development of room temperature NOx and NH3 sensors.