Photocatalytic Reduction of Carbon Dioxide with Iron Complexes

Photocatalytic CO2 reduction for fuel production has attracted much attention due to its potential for simultaneously solving energy and global warming problems. As a molecular catalyst, earth-abundant and ecofriendly iron complexes take the advantages of adjustable structure, rich valence, and easy synthesis, exhibiting good CO2 photocatalytic reduction performance, and hence have attracted much attention in the field of CO2 photocatalytic reduction. This review focuses on the recent progress in photocatalytic reduction of CO2 based on iron complexes. First, the homogeneous photocatalytic CO2 reduction systems using iron complex as catalyst, including iron porphyrin, iron polypyridine and iron pentadentate complex, are summarized Visible-light-driven CO(2 )reduction system is generally composed of three basic components; photosensitizer for absorption of visible light, catalyst for catalytic reduction of CO2, and sacrificial electron donors for providing electrons in reduction reaction. Beyond catalytic efficiency, CO2 photoreduction is a multi-electron transfer process boosted by the catalysts and inevitable competition with hydrogen evolution is a general issue for molecular catalysis of the CO2-to-CO conversion, therefore the selectivity of the products is an important indicator. The selectivity and efficiency could be tuned by changing the ligand of iron complex, photosensitizer and sacrificial electron donors. Moreover , the mechanisms for the homogeneous photocatalytic CO2 reduction, including catalyst activation and reduction process, are deciphered in detail. Second, the recent works of heterogeneous catalytic systems, which combine semiconductor nanomaterials/quantum dots with metal iron complexes as catalysts, are introduced. Considering the superior stability and fairly strong light absorption capacity of inorganic materials to the organic counterparts , the solid nanomaterials can be used as the photosensitizers to incorporate with the molecular catalysts. At the end, the current issues and perspectives on photocatalytic reduction of CO2 based on iron complexes are discussed. For examples, porphyrin metal organic frameworks become a new research interest, and the design and construction of iron porphyrin metal organic frameworks is a promising way for getting new photocatalytic systems functioning in aqueous conditions. Besides, further efforts could be made on the mechanistic studies, especially the 8e(-)/8H(+) reduction to methane.