Ultrasensitive NO2 gas sensing performance of two dimensional ZnO nanomaterials: nanosheets and nanoplates

Highly sensitive NO2 gas sensors with low detection limit are vital for practical application in air pollution monitoring. Here, the NO2 gas sensing performance of porous ZnO nanosheets and nanoplates were investigated, with different shape and thickness. It was found that ultra-thin ZnO nanoplates had a higher sensitivity than coral-like ZnO nanosheets. The results were attributed to the high specific surface and very small thickness of the ultrathin nanoplates. The nanoplates have indeed a thickness of 15 nm compared to that of the nanosheets which is 100 nm, and a BET surface area of 75 m2/g, while that of the nanosheets is 6 m2/g. The chemosensor based on ultra-thin ZnO nanoplates shows a response (calculated as the ratio between the resistance of the sensor in the presence of the gas and in its absence) of 76 to 0.5 ppm of NO2 at 200 °C, with a theoretical detection limit of 3 parts per trillion and a selectivity higher than 760 towards acetone, ethanol, isopropyl alcohol, triethylamine, SO2 and CO. The specific surface and the small thickness of the ultra-thin nanoplates contribute to its highly improved sensing performance, making it ideal for NO2 gas sensing.