Constructing a biomimetic TiOF@PCN-222-Fe Z-scheme heterojunction using self-assembled -cysteine for CO visible light photoreduction.

Biomimetic synthesis MOF-based catalysts to construct a Z-scheme heterojunction provides opportunities for enhancement of visible light photocatalytic CO reduction efficiency. Herein, a TiOF@PCN-222-Fe heterojunction was designed using the -cysteine agglomerant to simulate the structure of cytochrome oxidase. -cysteine axially coordinated with Fe in the ferroporphyrin moiety of PCN-222-Fe through the -SH group and coordinated with Ti in TiOF through the -COOH group. This heterojunction enhances photocurrent and conductivity, thus improving CO visible light photocatalytic activity. Various characterization methods including EXAFS and theoretical calculations demonstrated that the band bending of TiOF and PCN-222-Fe occurred through -cysteine coordination and a Z-scheme heterojunction was formed to efficiently separate photogenerated carriers. Thus, TiOF accumulates electrons and acts as the active center of CO reduction, PCN-222-Fe accumulates holes and acts as the active center of water oxidation, and -cysteine provides the transmission pathway of protons. The introduction of F element in TiOF lowered the valence band, which produced energetic holes that transferred to the valence band of PCN-222-Fe for water oxidation. This strategy provides unique insights into improving the efficiency of CO visible light photoreduction by biomimetic design of Z-scheme heterojunctions.