Fabrication Of The Formaldehyde Gas Sensor And Study Of The Sensing Properties

The damage of indoor HCHO to human health is self-evident. So the detection of low-level HCHO has been becoming the hot spot of the current research. In this paper, the author prepared the nanocrytalines TiO₂ doped- TiO₂ and In₂O₃ by sol-gel method. The crystal structure, particle size and surface properties of the samples were characterized by means of X-ray diffraction(XRD), Transmission electron microscopy(TEM) and Brunaner-Emmett-Teller(BET) surface areas. Under the same conditions, Ag-doped TiO₂ has larger BET surface areas than the pure one.The HCHO gas sensor were prepared, In order to inprove the sensitivity and selectivity of the sensors, the author also doped different metal oxide with TiO₂. The sensitive properties of the samples were also investigated. It was found that the doped sensor has a better sensitivity and higher selectivity to HCHO than the pure one. The sensitivity of sensor, which was prepared with 5% Ag-doped TiO₂ calcined at 500℃, was highest. With the optimum working current 124 mA, the sensitivity of sensor was approximate to 4 at its detection limit 10 ppm, its recovery time was 9 S whereas response time was no more than 1 S. The sensors also exibit better stability.Pure In₂O₃ has a favorable sensitivity in nature. Sensitivity has something to do with the calcination temperature of the material. It is revealed that the sensitivity appropriate to 5 when the material calcined at 500℃for 2 h. With the optimum working current 100 mA, its response time was 50 S whereas recovery time is 3 min.