Wenbo Lu

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.

Enhanced Room Temperature Oxygen Sensing Properties of LaOCl–SnO2 Hollow Spheres by UV Light Illumination

In this paper, a facile and elegant Green Chemistry method for the synthesis of SnO2 based hollow spheres has been investigated. The influences of doping, crystallite morphology, and operating condition on the O2 sensing performances of SnO2 based hollow-sphere sensors were comprehensively studied. It was indicated that, compared with undoped SnO2, 10 at. % LaOCl-doped SnO2 possessed better O2 sensing characteristics owing to an increase of specific surface area and oxygen vacancy defect caused by LaOCl dopant. More importantly, it was found that O2 sensing properties of the 10 at. % LaOCl-SnO2 sensor were significantly improved by ultraviolet light illumination, which was suited for room-temperature O2 sensing applications. Besides, this sensor also had a better selectivity to O2 with respect to H2, CH4, NH3, and CO2. The remarkable increase of O2 sensing properties by UV light radiation can be explained in two ways. On one hand, UV light illumination promotes the generation of electron-hole pairs and oxygen adsorption, giving rise to high O2 response. On the other hand, UV light activates desorption of oxygen adsorbates when exposed to pure N2, contributing to rapid response/recovery speed. The results demonstrate a promising approach for room-temperature O2 detection.

Ultrahigh photosensitivity and detectivity of hydrogen-treated TiO2 nanorod array/SiO2/Si heterojunction broadband photodetectors and its mechanism

It is demonstrated that hydrogen treatment as a simple, effective strategy can greatly improve the broadband photo-responsive performance of pristine TiO2 nanorod arrays (NRAs)/SiO2/n-Si heterojunctions. The hydrogen-treated TiO2 NRAs/SiO2/n-Si heterojunction shows a stable, repeatable and broadband photo response from 365 nm to 980 nm at 100 μW cm−2. The responsivity (R) of H:TiO2 NRAs/SiO2/n-Si approaches the ultrahigh value of 468 A W−1 and it has an outstanding detectivity (D*) of 1.96 × 1014 cm Hz1/2 W−1 and an excellent sensitivity (S) of 2.63 × 107 cm2 W−1, in contrast to the values of R (10−6–10−1 A W−1) or S (2 × 103 cm2 W−1) from reported TiO2 nanofilm/TiO2 NRAs/n-Si(111) photodetectors, indicating a huge responsivity enhancement of up to 4–8 orders of magnitude. Additionally, the response and recovery time are extremely short (3.5–3.9 ms). The comprehensive characteristics make the device stand out among the previously reported 1D metal oxide nanostructure/Si based photodetectors. In fact, the R, S and D* values of the heterojunction are 2–4 orders of magnitude higher than those of some new 2D nanomaterials/Si based photodetectors. The excellent photo-responsive performance may be attributed to the energy band structure of the TiO2@TiO2−xHx core/shell structure, the interface effect of the TiO2@TiO2−xHx/Si heterojunction, etc. This research provides a new concept for the design of other metal oxide based heterojunction photodetectors.