Construction\nof Covalent\nOrganic Frameworks with Partly\nCondensed Networks for Photocatalytic Hydrogen Evolution

Abstract

Covalent\norganic frameworks (COFs) are typically designed\nby topologically\ndirected condensation reactions to form the desired networks containing\nthe respective vertex and edge linker units. In general, the building\nblocks in the frameworks are always complementarily and fully connected\nto the frameworks. In this work, we showed the design and synthesis\nof two COFs, TPE-TPB-A and TPE-TPB-B, which were constructed from\nthe same monomers. Both exhibited good crystallinity and similar BET\nspecific surface area but different XRD patterns. Combined with structure\nsimulation and experimental data, TPE-TPB-A was determined to be connected\nby a normal fully bonded [4 + 4] pathway, while TPE-TPB-B was constructed\nvia an unusual [4 + 2] pathway with unreacted dangling formyl groups.\nMore importantly, partly condensed TPE-TPB-B with exposed formyl\ngroups exhibited more favorable physical/chemical properties than\nfully condensed TPE-TPB-A for photocatalytic hydrogen evolution (PHE),\nsuch as improved hydrophilicity and better charge separation and transportation.\nRemarkably, the average PHE rate of TPE-TPB-B was measured to be more\nthan 10 times higher than that of TPE-TPB-A under visible-light irradiation\nwith platinum as a cocatalyst and ascorbic acid as a sacrificial agent.\nThese results open up possibilities toward partly condensed COFs for\nvarious applications.