Modulating the local electron density at built-in interface iron single sites in Fe-CN/MoO3 heterostructure for enhanced CO2 reduction to CH4 and photo-Fenton reaction

The catalytic efficiency of heterogeneous photocatalytic CO₂ reduction and photo-Fenton H₂O₂ activation is closely related to the local electron density of reaction center atoms. However, electron-hole recombination from random charge transfer significantly restricts the targeted electron delivery to the active center. Herein, Fe-C₃N₄/MoO₃ heterojunction with interfacial coordination of atomically dispersed Fe-N₄ sites with the O interface of MoO₃ was synthesized by simple hydrothermal method. Based on the experimental results and density functional theory calculation (DFT), the heterojunction structure fosters accelerated interfacial electron transfer due to directional interfacial electric field (IEF) between Fe-CN and MoO heterogeneous interfaces, and the interfacial bond between Fe-N₄ sites and O at the built-in interface regulates the local electron density of Fe-N₄ active center. DFT further reveals that the interfacial electron flow and concentrated electron density at Fe-N₄ sites result from the coordination between Fe-N₄ and MoO₃ interfaces. This directs electron flow towards the Fe center, significantly enhancing CO₂ adsorption and H₂O₂ conversion efficiency. PDOS analysis shows that the d_yz and d_z² orbitals of the isolated Fe atom in Fe-CN overlap with the p_z orbital of the O atom in MoO₃, playing a pivotal role in CO₂ adsorption. Consequently, the Fe-CN/MoO₃ heterojunction demonstrated highly efficient photocatalytic CO₂ reduction to CH₄, coupled with benzyl alcohol oxidation and photo-Fenton tetracycline degradation. These findings offer a promising multifunctional catalyst strategy for the development of energy conversion and environmental remediation.