The transformation of a bimetal carboxylate-MOF into a phosphonate-based MOF as a multifunctional photocatalyst

Abstract

Over the last ten years, there has been significant ongoing development of metal–organic framework (MOF) catalysts designed for artificial photosynthesis, converting solar energy into chemical fuels. In contrast to carboxylate-based MOFs with poor water or moisture stability due to the lower coordination capabilities of carboxylate linkers, phosphonate-based MOFs are capable of having a robust framework and thus can act as photocatalysts in aqueous systems; however, phosphonate-based MOFs are difficult to synthesize because of crystallization challenges. Here, a thermochemically induced substitution strategy was first proposed for the construction of a phosphonate-based MOF (P-CT-MOF) from a bimetal carboxylate-MOF. Meanwhile, the electronic structure can be regulated, the band structure and active sites can be optimized, and the framework of the MOF can be stabilized. P-CT-MOF exhibits superior activity and selectivity in photocatalytic CO₂ reduction and photocatalytic oxygen evolution, affording a CO production rate as high as 3650.3 μmol h⁻¹ g⁻¹ and oxygen production of 602.1 μmol. Structural analyses indicate that the incorporation of phosphonate groups into P-CT-MOF contributes to: (i) improved charge separation, accelerating electron transfer within the LMCT state and enhancing transfer efficiency; (ii) increased Lewis acidity, promoting the adsorption and activation of CO₂ and H₂O molecules; and (iii) bandgap narrowing and light absorption range extension, alongside enhanced MOF stability. This work represents an example of the preparation of a phosphonated MOF as an efficient approach to construct photocatalysts.