Stability of Metal-Organic Frameworks in non-thermal Atmospheric Plasma

Abstract Metal organic frameworks (MOFs) are a promising class of materials to be used in combination with non-thermal atmospheric plasma for applications in plasma catalysis. MOFs offer large porosity and the potential for tailored, well-defined surface sites for catalytic reactions, but are limited in their thermal stability. This stability problem can be overcome by the use of plasma-generated excited species or radicals, which allow reactions to be carried out at much lower reaction temperatures. However, there is still a need to study and understand MOF–plasma interactions. Therefore, the stability of nine selected MOFs in contact with N2/H2 dielectric barrier discharge plasma has been systematically studied by in-plasma treatment (IPT). The detailed characterisation of the MOF before and after the plasma treatment shows that zeolitic imidazolate frameworks (ZIFs), with metal-nitrogen bonds and linkers containing a methyl (ZIF-8, ZIF-67) or an ethyl (MAF-5, MAF-6) group can maintain their porosity, chemical composition and crystallinity even after several hours of plasma exposure. In contrast, ZIF-71 which contains Cl-functionalised imidazolate linker, is unstable already after only tens of minutes of plasma treatment. Other MOFs such as ZIF-7 and those with metal-oxygen bonds, i.e., Al-CAU-10, Ce/Zr‑CAU-24, and Zr-UiO 66, (partially) degrade when treating them at temperatures higher than 150 °C for 1 h, indicating that they are more suitable for post-plasma catalysis processes. The identified stable MOFs are ideal candidates for future studies of plasma catalysis, where these MOFs will be modified or decorated with reactive sites for the reactions of interest.