3D ZnO/ZIF-8 Hierarchical Nanostructure for Sensitive and Selective NO<sub>2</sub> Sensing at Room Temperature

Abstract

Gas sensors based on semiconductor metal oxides (SMOs) have gained widespread attention for Internet of Things applications; however, high operating temperatures and low gas selectivity limit their applications. Recently, metal-organic frameworks (MOFs) have demonstrated potential in enhancing gas selectivity through the physical filtration of gas molecules based on their kinetic diameters. However, their application has been predominantly limited to simplistic nanostructured sensors. These sensors exhibit inherently inferior gas sensor performance compared to three-dimensional nanostructure gas sensors. In this study, a highly periodic, 3D hierarchical ZnO/ZIF-8 nanostructure is fabricated for photoactivated gas sensing at room temperature. Under UV illumination, the gas sensor exhibited a 17-fold enhancement in gas response toward 0.1 ppm NO2 compared to pristine ZnO. In addition, the ZIF-8 coating selectively increased the NO2 gas response compared to ethanol, acetone, and toluene gases, thereby improving the gas selectivity. The gas response improvement by the ZIF-8 layer coating, which has not been achieved by previous studies, is based on enhanced photoactivation by the solid interaction between ZIF-8 and ZnO. These results provide a systematic background for controlling the layer thickness of SMO-MOF nanostructures and the catalytic role of MOF in photoactivated gas sensing.