Large-Scale Synthesis of Hierarchically Porous ZnO Hollow Tubule for Fast Response to ppb-Level H₂S Gas

Response and recovery time to toxic and inflammable hydrogen sulfide (H₂S) 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 H₂S 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 m²·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 H₂S 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 H₂S performances are mainly related to the inherent characteristics of hierarchically porous hollow tubular structure and the surface-adsorbed oxygen control type mechanism.