Deactivation of porphyrin metal-organic framework in advanced oxidation process: Photobleaching and underlying mechanism

Porphyrin metal-organic frameworks (MOFs) are widely used in photocatalytic advanced oxidation processes (AOP). However, the stability and deactivation of MOFs, crucial for reusability, have been understudied compared to their catalytic activity. We investigated photobleaching in porphyrin MOFs PCN-224-M (M= H2, Fe, Co, Cu, Zn) under visible light and H2O2. The MOFs exhibited crystallinity loss, ring-opening cleavage, and linker degradation. Photobleaching resulted from direct redox reactions between porphyrin sites and H2O2. Metal-oxo-porphyrin intermediates played a key role in the "group effect," with different functional groups affecting the photobleaching rate: PCN-224-Fe ≈ PCN-224-Co > PCN-224-H2 > PCN-224-Cu ≈ PCN-224-Zn. This trend related to chelated metal ions' electronic structures and their propensity for metal-oxo intermediate formation, establishing a structure-stability relationship. Our study enhances understanding of deactivation mechanisms in porphyrin MOFs during AOP, aiding the design of resilient and efficient MOF catalysts for environmental applications.