Interfacial AssemblyImmobilization of Tripodal IronTerpyridyl Coordination Oligomers on Carbon Nitride for EfficientPhotocatalytic CO₂ Reduction

Surface modification of cheap light-absorbing materials by noble-metal-free molecular catalysts to construct high efficiency photocatalytic systems has recently attracted great research interest but remains a great challenge. Here, we constructed carbon nitride-based composite photocatalysts through interfacial covalently assembling tripodal Fe­(II)-terpyridyl (Fe–TerPyTa)_<i>n</i> coordination oligomers on oxidized graphitic carbon nitride (O–C₃N₄) via a surface-initiated alternative reaction between TerPyTa and Fe­(BF₄)₂. The obtained O–C₃N₄@(Fe–TerPyTa)_<i>n</i> possesses visible-light-absorbing C₃N₄ and active Fe–TerPyTa with superior capability in photocatalytic CO₂ reduction. Due to the well-defined structure and integrated functionality, the O–C₃N₄@(Fe–TerPyTa)₁ hybrid catalyst displays significantly enhanced catalytic performance in CO₂ reduction with outstanding CO selectivity (almost 100%) and a maximum CO evolution rate of 91.1 μmol g^–1 h^–1, which is nearly 100-fold higher than that of pristine O–C₃N₄. The fluorescence emission, time-resolved fluorescence, and electrochemical impedance spectrum studies indicate that the improved catalytic efficiency is mainly attributed to the direct covalent and coordinative interactions between the oligomer and the O–C₃N₄. Such a configuration can enhance the charge transfer from the O–C₃N₄ to the redox center of Fe–TerPyTa, which further passes the electrons to the CO₂ molecules to produce CO. Moreover, due to the kinetical preference for electrons to reduce H₂O-to-H₂, the reducing products can be regulated from pure CO to its CO/H₂ mixture (analogue of syngas) with tunable ratios by changing the water content in the reaction solution.