Construction of ZnO@ZIF-8 Core–Shell Heterostructure for Enhanced Formaldehyde Selective Performances at Room Temperature

Abstract

Zinc oxide (ZnO) nanorods were synthesized by hydrothermal method, and ZnO@ZIF-8 nanorods with core–shell heterostructure were prepared by water bath synthesis method. The ZnO nanorods were synthesized by water bath and violently stirred at 50°C and 4 h as the optimal reaction time, in which ZIF-8 was a zeolite imidazolic acid skeleton structure. ZnO nanorods serve as the template for the growth of ZIF-8 shell and provide Zn²⁺ ions for its growth. By X-ray diffraction (XRD), it is proved that the nanorods are composed of ZnO and ZIF-8. By field emission electron microscopy (SEM) and transmission electron microscopy (TEM), it is proved that ZnO@ZIF-8 is composed of ZnO in the middle core and ZIF-8 in the outer shell. According to the test by BET, the specific surface area of ZnO and ZnO@ZIF-8 nanorods is 2.16 and 85.08 m²/g, respectively, and the specific surface area of the latter is much larger than that of the former. Compared with ZnO nanorod sensors, the ZnO@ZIF-8 sensor exhibits comparable response levels to formaldehyde, and the response to other test gases is decreased, and the screening ability of formaldehyde has been improved to a certain extent, because the pore size of the ZIF-8 shell has different restrictions on molecules of different sizes. This study shows that coating ZIFs on the surface of metal oxides is an effective method to improve the performance of gas sensors.