Water pre-adsorption effect on room temperature SnO2 nanobelt ethanol sensitivity in oxygen-deficient conditions

The water adsorption effects on room temperature ethanol sensitivity of a SnO2 single crystal nanobelt was studied. SnO2 nanobelt showed better electrical conductivity in air than in vacuum. The current increased linearly with relative humidity in air and with water concentration in vacuum. In the presence of water vapor, the SnO2 nanobelt electrical response was quite different, depending on the H2O and C2H5OH molecules adsorption sequence. The current response to ethanol gas increased substantially when water was pre-adsorbed. However, no change was found without water pre-adsorbtion. This interesting behavior is ascribed to competition between the H2O and C2H5OH molecules trying to adsorb on oxygen sites at the tin oxide surface. Dissociated water acts as the surface conduction channel resulting in better conductivity, while ethanol is physisorbed without water pre-adsorption. Based on this sensing mechanism, SnO2 nanobelt can be used as a highly efficient ethanol detector in humid air.