Non-noble copper ion anchored on NH2-MIL-101(Fe) as a novel cocatalyst with transient metal centers for efficient photocatalytic water splitting

•The noble-metal-free CuII/CuI was used as cocatalysts via transient CuII/CuI centers.•The non-traditional LLCMT pathway was formed as a novel charge transfer channel.•The Cu species transient center can enhance the charge carriers separation efficiency. The earth-abundant copper species anchored on the -NH2 of NH2-MIL-101(Fe) as noble-metal-free cocatalysts via transient CuII/CuI centers were obtained via a convenient synthesis technique to achieve excellent photocatalytic hydrogen evolution performance in the dye sensitization system. The prepared sample 6Cu-NM-101 exhibited the best hydrogen evolution activity of 5770.96 μmol·g−1·h−1, which was 4.06 times higher than the original NH2-MIL-101(Fe). A series of characterization tests, especially the CV and the Auger Cu LMM, demonstrated that the transient CuII/CuI center played a significant part in the novel ligand to linker metal charge transfer (LLMCT) process. In other words, the electrons could transfer from the lowest unoccupied molecular orbital (LUMO) energy level of the excited state Eosin Y (EY*) to the transient CuII/CuI center to further accelerate the carrier transfer and separation rate. Our work provided a more convenient and effective strategy to prepare various earth-abundant metal ions based on MOFs as low-cost cocatalysts via transient metal centers to boost the photocatalytic hydrogen evolution performance.