Engineering molecular heterojunctions in 2D MOFs for efficient charge separation and CO₂ photoreduction

A molecular-level heterojunction is achieved by coordinating zinc porphyrin (Zn-TIPP) units onto the surface of a two-dimensional metal-organic framework nanosheet (Cu-HHTP), resulting in a metal-porphyrin-modified 2D MOF heterostructure (Zn-TIPP/Cu-HHTP). Under visible light irradiation, CO₂ is photocatalytically converted to formic acid, with a production rate of 1.08 mmol g^-1 h^-1 and a selectivity of 94%. This catalytic activity represents an eightfold enhancement compared to that of pristine Cu-HHTP and surpasses that of most reported MOF-based photocatalysts. The substantial enhancement in catalytic performance can be attributed to the synergistic effects derived from molecular-level integration, which enables accurate interfacial charge regulation, promotes charge separation and substantially decrease the energy barrier of the rate-determining step (*OCHO → *HCOOH). This study establishes a design strategy for molecular heterojunctions in advanced metal-organic framework photocatalysts. It demonstrates that precise molecular-level modification and functional unit integration can concurrently optimize interfacial charge kinetics, enhance catalytic activity, and regulate product selectivity, thereby facilitating efficient solar-driven CO₂ conversion.