Vapor Deposited Zeolitic Imidazolate Framework-8 Derived from Porous ZnO Thin Films

In recent years, the vapor deposition of zeolitic imidazolate framework-8 (ZIF-8) has gained high attraction due to its good scalability, conformality, and thickness control. The present study provides new fundamental insights regarding the vapor deposition of ZIF-8 from zinc oxide (ZnO). During synthesis, ZnO thin films with different percentages of open porosity (14.5%–24%) were subjected to a 2-methylimidazole vapor for different conversion times (20 min–24 h). For the first time, the impact of the porosity of ZnO thin films onto the converted ZIF-8 is investigated. Grazing incidence X-ray diffraction reveals randomly oriented crystallites of ZIF-8, which already appear after 20 min of conversion. The thickness, roughness, and average particle height of the ZIF-8 layers increase with the conversion time, reaching values up to (172 ± 20) nm, (29 ± 3) nm, and (113 ± 8) nm, respectively, for ZIF-8 obtained from ZnO with 14.5% open porosity. At long conversion times (i.e., 24 h), the results hint at greater precursor porosities resulting in lower thicknesses of ZIF-8, as the thickness, roughness, and average particle height for ZIF-8 obtained from 24%-porous ZnO show values of (132 ± 20) nm, (25 ± 3) nm and (80 ± 8) nm, respectively. Additionally, the potential of the ZIF-8 layers as a photocatalyst for the degradation of the organic dye methylene blue was studied. The ZIF-8 enhances the degradation by approximately 8% when compared to degradation without a photocatalyst.