Below-room-temperature solution-grown ZnO porous nanosheet arrays with ppb-level NO2 sensitivity under intermittent UV irradiation

Abstract

It is difficult for a chemiresistive metal oxide gas sensor to operate at room temperature due to the poor desorption ability of the adsorbed gases during recovery. UV irradiation helps to clean the surface of metal oxides, but it is also unfavorable for gas adsorption. In this work, intermittent UV irradiation, i.e., UV on (off) before (after) exposure to a target gas, is found to remarkably enhance the sensitivity of ZnO toward NO2. Porous nanosheet arrays of ZnO have been in-situ grown on the sensor chip in an alkaline bath at a low temperature of 8 degrees C. Heterogeneous growth of nanosheet arrays and homogeneous growth of nanosheet-constructed spheres take place on the substrate and in the bulk solution, respectively. The as-grown ZnO nanosheet arrays contain not only macropores between nanosheets but also mesopores within the nanosheets, which endow them superior NO2 sensing properties under intermittent UV irradiation. The growth kinetics of ZnO porous nanosheet arrays and the mechanism of the NO2 sensing under intermittent UV irradiation have been elaborated.