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

Abstract

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 (IrIII-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 ∼120 h–1 which is 3.4-fold higher than that of bulk IrIII-MOC-NH2 and two orders of magnitude higher than that of the classical metal–organic framework counterpart (IrIII-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.

Metallocavitins as Promising Industrial Catalysts: Recent Advances

“…Thus, Ir complex incorporated into Zr-MOC-NH 2 was used for CO 2 photoreduction. DFT calculations and in situ IR show that the Ir(III) complex is the catalytic center and −NH 2 in the cavity plays a synergetic role in the stabilization of the transition state and Ir•CO 2 intermediate (Qi et al, 2021). Under irradiation by visible light, the single Ir III -MOC-NH 2 cage can convert CO 2 into CO with a selectivity of 99.5% and a TOF of 120 h −1 , which is 3.4 times higher that of bulk Ir(III) complex and 100 times higher than that of the classical MOF counterpart, Ir III -Uio-67-NH 2 (Figure 3A, Qi et al, 2021).…”

“…DFT calculations and in situ IR show that the Ir(III) complex is the catalytic center and −NH 2 in the cavity plays a synergetic role in the stabilization of the transition state and Ir•CO 2 intermediate (Qi et al, 2021). Under irradiation by visible light, the single Ir III -MOC-NH 2 cage can convert CO 2 into CO with a selectivity of 99.5% and a TOF of 120 h −1 , which is 3.4 times higher that of bulk Ir(III) complex and 100 times higher than that of the classical MOF counterpart, Ir III -Uio-67-NH 2 (Figure 3A, Qi et al, 2021). Photocatalytic CO 2 R with the MIL-100(Fe)-CsPbBr 3 composite having a high specific surface area, an enhanced solar light response, and an improved charge carrier separation resulted in an excellent photocatalytic performance with 20.4 μmol CO produced per gram of the photocatalyst during 1 hour under visible light irradiation (Cheng et al, 2020).…”

Recent advances in photocatalytic renewable energy production

“…Li et al [139] presented a bioinspired MOF with flexible Cu and Ni dual-metal-site pairs (DMSPs) that exhibited self-adaptive behavior to fit mutative C1 intermediates, realizing visible-light-driven CO 2 reduction to CH 4 . The Cu and Ni DMSPs were incorporated into MOF-808 to form MOF-808-CuNi, leading to a production rate of 158.7 μmol•g -1 •h -1 and a promoted CH 4 selectivity of 97.5%.…”

Photocatalytic reduction of low-concentration CO2 by metal–organic frameworks

“…In recent years, a lot of efforts have been devoted to photochemical CO 2 reduction and a great number of photocatalysts have been developed, including metal oxides and sulfides, 9,10 g-C 3 N 4 -based photocatalysts, [11][12][13] metal-organic frameworks (MOFs), [14][15][16][17][18] and covalent organic frameworks (COFs); 19,20 high CO 2 photoreduction activity in a pure CO 2 atmosphere has been achieved. In contrast, for low-concentration CO 2 reduction, there are only a few reports using N 2 /Ar to dilute high-purity CO 2 .…”