Functional Integration of [Ir(ppy)₂(H2dcbpy)] and a Molecular Nickel Complex into Metal-Organic Frameworks for Photocatalytic CO2 Reduction

Developing multifunctional photocatalysts that efficiently convert CO₂ into valuable chemical products (e.g., CO, CH₄, HCOOH, and CH₃OH) is essential for achieving sustainable development. To address this challenge, we report a remarkable multifunctional metal-organic framework (MOF)-based photocatalyst, termed UiO-67-Ni-Ir, which has been elegantly crafted through an in situ synthesis strategy. This promising catalyst contains a highly efficient light-absorbing iridium unit, [Ir(ppy)₂(H2dcbpy)] (where ppy = 2-phenylpyridine, H₂dcbpy = 2,2′-bipyridine-4,4′-dicarboxylic acid), referred to as Ir-PS, in conjunction with a catalytically active nickel center. The broad absorption of visible light of the Ir-PS unit empowers the efficient CO₂ reduction reactions under visible light illumination. The photocatalyst UiO-67-Ni-Ir exhibits exceptional photocatalytic performance, producing 5800 µmol g⁻¹ of formate (HCOO⁻) over a 6 h period with a remarkable selectivity of 96.5%. This high formate yield is further supported by a turnover number (TON) exceeding 51 during the same photocatalysis run, which is ten times higher than that of the corresponding homogeneous system. Moreover, this catalyst is completely heterogeneous and recyclable, making it an attractive candidate for the photocatalytic conversion of CO₂ to formate under visible light irradiation. Furthermore, a plausible mechanism has been proposed based on the photophysical and electrochemical study along with density functional theory (DFT), which provides a comprehensive understanding of the underlying catalytic process.