Study On The Formaldehyde Gas Sensor Based-On TiO₂ Hollow Sphere

Formaldehyde is a serious polluting gases in human life. Semiconductor oxide sensor as one of the detection way for formaldehyde. However, current reports show that the semiconductor oxide sensor often need to work at high temperatures(>300?) to detect ppm level of formaldehyde. Moreover, the detection limit was still above 5 ppm that could not meet the requirements in some practical applications such as air quality monitor in house.Room temperature chemoresistive gas sensors could significantly decrease the demand of the power consumption and are thus highly desirable in practical applications. We here reported that the chemoresistive sensors using the fabricated mesoporous hollow TiO2 microspheres indicated an extreme high sensitive to ppb-level VOCs such as formaldehyde at room temperatures with the assistance of UV LED photon energy (-4 mW). The mesoporous hollow TiO2 microspheres were prepared by a pyrolysis method using carbon as the sacrifice template. The hollow microspheres shows much improved photon response features. The operation temperatures of hollow TiO2 based chemoresistive gas sensors could be significantly driven down to room temperature by the several-microwatts-powered UV photon energy offering significant savings on total power consumption. With the ultra thin walls of the hollow TiO2 microspheres, the detection limit could go down to ppb-level and response/recovery time could decrease less than 1 minute which significantly surpass the properties shown by similar various nanostructured TiO2 reported in literature. To further investigate the relationship between the thickness of the shell to gas sensing properties, we prepared the 8nm thickness shell TiO2 hollow spheres, the results showed gas sensing performance has improved, but the stability of the sensor is reduced. By dipping method, this study prepared a TiO2 hollow sphere doping with 10% of In2O3 nanoparticles. The sensing results shows that the n-n microheterojunction has significant improved the sensor's selectivity to 2-8ppm NO2.