Study On Preparation Of Nanostructure Tungsten Trioxide And The Gas-sensing Properties

The nanostructured WO3 was prepared by a hydrothermal method in this paper. The ammonium metatungstate((NH4)6W12O40·nH2O) was regared as the tungsten source and citric acid(C6H8O7) was considered as the morphology controlling agent.The effect of citric acid content, pH value, hydrothermal reaction temperature and reaction time on the morphology and phase of the nanostructured WO3 were studied. The nanostructured WO3 was characterized by XRD, SEM and TEM. The results showed that the diameter of tungsten trioxide nanorods was about 30 to 60 nm and the length was about 1 μm. The maximum length was 2.5 μm. The length to diameter ratio of tungsten trioxide nanorods was about 10 ~ 15 and the biggest length to diameter ratio was about 1:80. The thickness of nano platy tungsten trioxide was about 10 to 20 nm. Meanwhile, the growth mechanism of nanostructured tungsten trioxide was discussed. Gas sensitive performance of the gas sensor prepared by nanostructured tungsten trioxide was studied under the condition of ethanol, acetone, ammonia and formaldehyde four types of gases.Meanwhile, three gas sensors were further synthesed, including WO3 nanorods gas sensors, WO3 nanoplate gas sensors and WO3 nanoplate/nanorods gas sensors. Three kinds of gas sensors were made sensitivity test under the condition of ethanol, acetone, ammonia and formaldehyde four types of gases, respectively. In contrast, the sensitivity of gas sensors was WO3 nanoplate > WO3 nanorods > WO3 nanoplate/nanorods in four gases atmosphere of the ethanol, acetone, ammonia and formaldehyde.The results of gas sensing properties test showed that the optimum operating temperature of WO3 nanosheets gas sensors were 350℃, 300℃, 325℃, 250℃ in ethanol, acetone, ammonia and formaldehyde gas, respectively. The maximum sensitivity in ethanol, acetone, ammonia and formaldehyde gas was obtained: 25.4, 18.52, 30.29, 18.31, respectively, at 1000 ppm of gas concentration. The lowest concentrations of ethanol, acetone, ammonia and formaldehyde detected by WO3 nanosheets gas sensors was 50 ppm, 50 ppm, 25 ppm and 100 ppm. When ammonia gas concentration of 25 ppm, the sensitivity is 2.81, indicating that the gas sensor is extremely sensitive to low concentrations of ammonia.