Chemically Exfoliated Semiconducting Bimetallic Porphyrinylphosphonate Metal–Organic Layers for Photocatalytic CO₂ Reduction under Visible Light

In this paper, we report the first example of semiconducting porphyrinylphosphonate metal–organic framework (MOF) [Co­(Ni-H₇TPPP)₂]·8H₂O and its chemical exfoliation into ultrathin metal–organic layers (MOLs) with an electric conductivity up to 0.12 S cm^–1 at RT. Benefiting from the 2D layered structure possessing highly accessible metalloporphyrin-active motifs, a negatively charged surface, and a phosphonate-enhanced structural stability, the exfoliated MOL enables the material to behave as an efficient cocatalyst in coordination with positively charged [Ru­(bpy)₃]²⁺ to photocatalytically reduce CO₂ to CO in a high yield rate (3.16 × 10⁴ μmol g^–1 h^–1) and selectivity (81%). Spectroscopic studies engaging DRS, UPS, PL, EIS, and TPR unanimously point to the remarkable photocatalytic performance being a result of proper band alignment among the system components and great charge extraction capability of the cocatalyst. More importantly, by explicitly dissecting the band structure and charge transport behavior, this study provides insights into catalyst design to afford a coherent energy flow in hybrid photocatalytic systems.