Covalent Organic Framework Controls the Aggregation of Metal Porphyrins for Enhanced Photocatalytic H Evolution.

Although different post modifications of covalent organic frameworks (COFs) have been developed for achieving hierarchical nanostructures and improved photocatalytic performance, the co-assemblies of COFs with small organic molecules were still rarely studied. Herein, COF/porphyrin composites, which were fabricated at room temperature, reveal that COFs surface can modulate the aggregation of metal porphyrins, which subsequently enhance the photocatalytic properties of COFs assemblies. Thus, the surface of COFs was decorated by porphyrins aggregations with varied thickness, dependent on the metal ions of porphyrins. Ni(II) meso-Tetra (4-carboxyphenyl) porphine (NiTCPP) formed discontinuous monolayer covering on COFs surface, while Pt(II) meso-Tetra (4-carboxyphenyl) porphine (PtTCPP) or Co(II) meso-Tetra (4-carboxyphenyl) porphine (CoTCPP) aggregated into multilayer coverage. Notably, even though NiTCPP did not show any advantages in terms of light absorption or HOMO/LUMO energy levels, COF/NiTCPP with the lowest porphyrin loading still exhibited the highest photocatalytic H evolution (29.71 mmol g h), which is 2.5 times higher than that of COF/PtTCPP or COF/CoTCPP. These results open new possibilities for making highly efficient photocatalysts upon the co-assemblies of COFs with small organic molecules.