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 Ti 6 -NH 2 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 %), Ti 6 -NH 2 (19 %) and under-darkness (9 %), respectively. Notably, an O 2 -based mechanism is proposed and the vital roles of Ti 6 -NH 2 and BTT are verified by DFT calculations. This work might facilitate the exploration of porous-crystalline-catalysts for selective biomass-valorization.