Covalent‐Bonding Oxidation Group and Titanium Cluster to Synthesize a Porous Crystalline Catalyst for Selective Photo‐Oxidation Biomass Valorization

The selective photo‐oxidation of biomass‐derived 5‐hydroxymethylfurfural (HMF) to 2,5‐furandicarboxylic acid (FDCA) is important due to its substitute‐role in polyester‐fabrication. Here, a titanium‐cluster based metal‐covalent organic framework nanosheet has been synthesized through the covalent‐coupling between Ti6‐NH2 and benzotrithiophene tricarbaldehyde (BTT). The integration of them endows the nanosheet with a visible‐light‐adsorption region, effective electron‐hole separation‐efficiency and suitable photo‐oxidation ability. Specifically, its photo‐selectivity for HMF‐to‐FDCA can be >95 % with ≈100 % conversion, which is more than 2, 5, and 10 times higher than MOF‐901 (43 %), Ti6‐NH2 (19 %) and under‐darkness (9 %), respectively. Notably, an O2‐based mechanism is proposed and the vital roles of Ti6‐NH2 and BTT are verified by DFT calculations. This work might facilitate the exploration of porous‐crystalline‐catalysts for selective biomass‐valorization. A titanium‐cluster‐based metal‐covalent organic framework nanosheet has been prepared through the covalent‐coupling between the Ti‐cluster and an oxidation group. The resulting nanosheets can be applied for highly selective photo‐oxidation of biomass HMF into FDCA.