Auxiliary ligand-coordinated nanoconfined hydrophobic microenvironments in nickel(ii)–acetylide framework for enhanced CO₂ photoreduction

Abstract

Metal–acetylide frameworks (MAFs), featuring metal-bis(acetylide) linkages (─C≡C─M─C≡C─), are emerging as a new class of 2D nanomaterials with promise in catalysis. Here, we report a new 2D NiII–acetylide framework, TPA-Ni(PR3)2-GYs, that incorporates the NiII(PR3)2 moiety [R = CH3 (Me), CH2CH3 (Et), and CH2CH2CH2CH3 (Bu)] into tris(4-ethynylphenyl)amine-based graphdiyne framework (TPA-GDY). As a result, TPA-Ni(PBu3)2-GY exhibits an exceptional photocatalytic CO2 reduction activity of 3807 µmol g−1 h−1 and a high selectivity of 99.4% for CO production upon visible light irradiation. Mechanistic investigations reveal a strong orbital matching effect between the d orbitals of NiII and the p orbitals of the alkynyl C atoms in organic ligands, which not only accelerates the transfer and separation of photogenerated charge carriers but also reduces the reaction potential barrier for the formation of *COOH intermediates. Furthermore, the high hydrophobicity of the auxiliary coordinated ligands (trialkylphosphines) to Ni center, particularly tributylphosphine, creates a nanoconfined space that enhances both the accessibility of CO2 and the utilization of NiII catalytic active sites while inhibiting hydrogen evolution. This study highlights the benefit of modulating the microenvironment around the coordinated metal center to enhance the performance of catalysts with direct metal–acetylide bonding.