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.

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Two-dimensional ultrathin porous α-MoO3 nanosheets with oxygen vacancies were synthesized by a simple solvothermal method. The thickness of the precursor reaches 14 nm and is accumulated by sheets of 2–6 nm. The pore size is 2–10 nm on the surface. A gas sensor was assembled with the α-MoO3 nanosheets annealed at 400 °C (α-MoO3-400). The sensor based on α-MoO3-400 achieves the fastest response to trimethylamine (TMA) gas at relatively low operating temperature (133 °C). The response of the sensor is 198–50 ppm TMA and the detection limit is 20 ppb. In addition, the sensing mechanism is verified by experiment that the gas molecules adsorb on the surface of MoO3 and participate in the electron transfer of the semiconductor. DFT calculations suggest that MoO3 containing oxygen vacancy can increase charge transfer after TMA adsorbed.

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