Sensors for the nitrogen oxides, NO2, NO and N2O, based on In2O3 and WO3 nanowires

Sensing characteristics of ZnO, In2O3 and WO3 nanowires have been investigated for the three nitrogen oxides, NO2, NO and N2O. In2O3 nanowires of similar to 20 nm diameter prepared by using porous alumina membranes are found to have a sensitivity ( defined as the ratio of the sensor resistance in the gas concerned to that in air) of about 60 for 10 ppm of all the three gases at a relatively low temperature of 150 degrees C. The response and recovery times are around 20 s. The sensitivity of these In2O3 nanowires is around 40 for 0.1 ppm of NO2 and N2O at 150 degrees C. WO3 nanowires of 5 - 15 nm diameter, prepared by the solvothermal process show a sensitivity of 20 - 25 for 10 ppm of the three nitrogen oxides at 250 degrees C. The response and recovery times are 10 s and 60 s, respectively. The sensitivity is around 10 for 0.1 ppm of NO2 at 250 degrees C. The sensitivity of In2O3 and WO3 nanowires is not affected by humidity even up to 90% relative humidity. The study also reveals that the sensing mechanism for the three nitrogen oxides have a commonality in that the desorption of oxygen is a crucial step in all the cases.