Study on the selectivity difference of formaldehyde and ethanol induced by variation of energy gap in In2O3 hierarchical materials

Abstract

Poor selectivity has been one of the most serious problems restricting the development of metal oxide gas sensors. Obtaining sensing materials with excellent selectivity and studying the dominate factors and mechanism affecting selectivity are of great significance to the application and development of gas sensors. Here, we have prepared a series of In2O3 hierarchical spheres (HS) samples which exhibited distinct sensing performance toward formaldehyde and ethanol by varying the solvent-urea. In particular, In2O3-0.05 HS have shown excellent selectivity to formaldehyde at low temperature (180 °C). With the increase of reaction solute-urea, the selectivity of the sample to formaldehyde decreases, but the sensitivity to ethanol increases. The UV–vis absorption spectrum test shows that the variation of urea changes the energy gap of samples, leading to different selectivity toward ethanol and formaldehyde. Especially, the response of In2O3-0.05 HS to 100 ppm formaldehyde is 10 times higher than the response to other gas. And the response of In2O3-0.8 HS to 100 ppm ethanol is as high as 24 at 300 °C, which is 3 times higher than that of In2O3-0.05 HS, suggesting an obvious link between energy gap and sensing properties. This experiment not only promotes the understanding of relationship between sensing performance and energy gap, but also provides a new method for designing high-selectivity gas sensors.