NiO porous nanowall arrays have been successfully grown in situ on ceramic tubes by a hydrothermal reaction, combined with a calcination process. With such unique hierarchical pores, the array film sensor displayed excellent sensing performance toward H2S.

Response and recovery time to toxic and inflammable hydrogen sulfide (H 2 S) gas are important indexes for metal oxide sensors in real-time environmental monitoring. However, large-scale production of ZnO-based sensing materials for fast response to ppb-level H 2 S has been rarely reported. In this work, hierarchically porous hexagonal ZnO hollow tubule was simply fabricated by zinc salt impregnation and subsequently calcination using absorbent cotton as the template. The influence of calcination temperature on the corresponding morphology and sensing properties is also explored. The hollow tubules calcined at 600 °C are constructed from abundant cross-linked nanoparticles (∼20 nm). Its Brunauer−Emmett−Teller surface area is 31 m 2 •g −1 and the meso-and macroporous sizes are centered at 35 and 115 nm, respectively. The sensor with a lower detection limit of 10 ppb exhibits a fast response speed of 29 s toward the 50 ppb H 2 S rather than those of the reported intrinsic and doped ZnO-based sensing materials. Furthermore, the sensor shows a wide linear range (10−1000 ppb), good reproducibility, and stability. Such excellent trace ppb-level H 2 S performances are mainly related to the inherent characteristics of hierarchically porous hollow tubular structure and the surface-adsorbed oxygen control type mechanism.

Monodisperse, hierarchical α-MoO hollow spheres were fabricated using a facile template-free solvothermal method combined with subsequent calcination. Various quantities of Au nanoparticles (NPs) were deposited on the α-MoO hollow spheres to construct hybrid nanomaterials for chemical gas sensors and their BTX sensing properties were investigated. The 2.04 wt % Au-loaded α-MoO sensor can detect BTX effectively at 250 °C, especially, its responses to 100 ppm toluene and xylene are 17.5 and 22.1, respectively, which are 4.6 and 3.9 times higher than those of pure α-MoO hollow spheres at 290 °C. Besides, Au loading decreased the response times to toluene and xylene from 19 and 6 s to 1.6 and 2 s, respectively, lowered the working temperature from 290 to 250 °C as compared with those of pure α-MoO. The surface status of Au/α-MoO hollow spheres before and after contacting with toluene at 250 °C was analyzed through XPS technique. Possible oxidization product of toluene was confirmed by GC for the first time. The gas-sensing mechanism of the Au/α-MoO was speculated as the oxidation of toluene to water and carbon dioxide by chemisorbed oxygen and lattice oxygen. The possible reason related with improved gas-sensing properties of the Au-functionalized α-MoO was discussed.

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