Single Metal-Organic Cage Decorated with an Ir(III) Complex for CO2 Photoreduction

CO2 photoreduction is a promising avenue to alleviate climate change and energy shortage, and highly active and selective photocatalysts have been pursued. Discrete metal-organic cages (MOCs) with tunable structures and dispersion not only render integration of multiple functional moieties but also facilitate the accessibility of catalytic sites, yet the studies of MOCs on CO2 reduction are still underexplored. Herein, a single molecular cage of the Ir(III) complex-decorated Zr-MOC (Ir-III-MOC-NH2) is proposed for CO2 photoreduction. IrIII-MOC-NH2 shows high reactivity and selectivity in converting CO2 into CO under visible light. The selectivity is of 99.5% and the turnover frequency reaches similar to 120 h(-1) which is 3.4-fold higher than that of bulk Ir-III-MOC-NH2 and two orders of magnitude higher than that of the classical metal-organic framework counterpart (Ir-III-Uio-67-NH2). The apparent quantum yield is up to 6.71% that ranks the highest among the values reported for crystalline porous materials. Moreover, aggregation-induced deactivation of the Ir(III) complex is restrained after incorporating into MOC-NH2. The density functional theory calculations and dedicated experiments including cyclic voltammetry, mass spectrometry and in situ IR show that the Ir(III) complex is the catalytic center, and -NH2 in the framework plays the synergetic role in the stabilization of the transition state and CO2 adducts.

Automated summary

A novel single molecular cage of Ir(III) complex-decorated Zr-MOC has been proposed for CO2 photoreduction, showing high reactivity, selectivity, and apparent quantum yield. The catalytic center is the Ir(III) complex, while the -NH2 in the framework plays a synergetic role in stabilizing the transition state and CO2 adducts, leading to superior performance compared to classical metal-organic framework counterparts.