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.