Synthesis of nanowire bundle-like WO3-W18O49 heterostructures for highly sensitive NH3 sensor application.

Heterojunctions are very promising structures due to their hybrid properties, which are usually obtained via a multistep growth process. However, in this paper, WO3-W18O49 heterostructures are synthesized via a novel one-step approach by using isopropanol as reaction media and are applied in NH3 gas detection for the first time. The obtained WO3-W18O49 heterostructures with loose nanowire bundle-like morphology show a response value of 23.3 toward 500 ppm NH3 at 250 °C, which is 5.63 times higher than that of pristine W18O49. In addition, the WO3-W18O49 sensor also exhibits great dynamic response/recovery characteristics (13 s/49 s @ 500 ppm NH3), superb selectivity and low detection limit of 460 ppb. The substantial improvement in the response of WO3-W18O49 heterostructures toward NH3 can be explained by the formation of n-WO3/n-W18O49 heterojunctions that facilitate the generation of a more extended depletion layer as well as the enhancement of specific surface area and pore volume. Our research results open an easy pathway for facile one-step preparation of heterojunctions with high response and low cost, which can be used for the development of other high-performance gas sensors.

Ultra-sensitive NH3 sensor based on flower-shaped SnS2 nanostructures with sub-ppm detection ability.

Layered metal dichalcogenides (LMDs) semiconducting materials have recently attracted tremendous attention as high performance gas sensors due to unique chemical and physical properties of thin layers. Here, three-dimensional SnS2 nanoflower structures assembled with thin nanosheets were synthesized via a facile solvothermal process. When applied to detect 100ppm NH3 at 200°C, the SnS2 based sensor exhibited high response value of 7.4, short response/recovery time of 40.6s/624s. Moreover, the sensor demonstrated a low detection limit of 0.5ppm NH3 and superb selectivity to NH3 against CO2, CH4, H2, ethanol and acetone. The excellent performance is attributed to the unique thin layers assembled flower-like nanoarchitecture, which facilitates both the carrier charge transfer process and the adsorption/desorption reaction. More importantly, it was found that the sensor response enhanced with increasing oxygen content in background and was improved by 3.57 times with oxygen content increasing from 0 to 40%. The increased response is owing to the enhanced binding energies between SnS2 and NH3 moleculers. Theoretically, density functional theory was employed to reveal the NH3 adsorption mechanism in different background oxygen contents, which opens a new horizon for LMD based structures applied in various gas sensing fields.