Cu ions anchored in the porphyrin center act as transient metal centers of 2D-MOFs to enhance photocatalytic hydrogen production

Abstract

To improve charge transfer efficiency, non-noble metal Cu anchored in the porphyrin center can realize a new ligand-to-linker metal charge-transfer (LLMCT) process in 2D Ti-based porphyrin MOFs. Experimental results demonstrate that 2D Cu-PTM has the best hydrogen evolution activity (5465.689 μmol g⁻¹ h⁻¹), which is about 27.71 times the value of original 2H-PTM (197.224 μmol g⁻¹ h⁻¹). A series of characterization tests, particularly Auger Cu LMM and ESR, proved that the transient Cu^I/Cu^II center played an important role in the new LLMCT process. In brief, electrons can transfer from excited eosin Y (EY*) to the lowest unoccupied molecular orbital (LUMO) level of porphyrin and then transfer to the transient Cu^I/Cu^II center via a fast conjugated delocalized 18-π electron system of the porphyrin unit, which further accelerates the carrier separation and transfer rate. This work provides simpler and more effective tactics to anchor transition elements in 2D porphyrin MOFs and used non-noble metal ions as low-cost auxiliary catalysts to improve photocatalytic hydrogen evolution performance.