Ionic Liquid Modified Fe-Porphyrinic Metal–Organic Frameworks as Efficient and Selective Photocatalysts for CO₂ Reduction

Abstract

Porphyrin-based metal-organic frameworks (MOFs) are ideal platforms for heterogeneous photocatalysts toward CO₂ reduction. To further explore photocatalytic MOF systems, it is also necessary to consider their ability to fine-tune the microenvironments of the active sites, which affects their overall catalytic operation. Herein, a kind of ionic liquid (IL, here is 3-butyric acid-1-methyl imidazolium bromide, BAMeImBr) was anchored to iron-porphyrinic Zr-MOFs with different amounts to obtain IL<i>x</i>@MOF-526 (MOF-526 = Zr₆O₄(OH)₄(FeTCBPP)₃, FeTCBPP = iron 5,10,15,20-tetra[4-(4'-carboxyphenyl)phenyl]-porphyrin, <i>x</i> = 100, 200, and 400). IL<i>x</i>@MOF-526 series was designed to investigate the effects of the microenvironmental and electronic structural modification on the efficiency and selectivity of the photochemical reduction of CO₂ after introducing IL fragments. Compared to parent MOF-526, the production and selectivity of CO were greatly improved in the absence of any photosensitizer under visible light by the IL<i>x</i>@MOF-526 series. Among them, the CO yield of IL200@MOF-526 was up to 14.0 mmol g^-1 within 72 h with a remarkable CO selectivity of 97%, which is superior to that of MOF-526 without BAMeIm⁺ modification and other amounts of BAMeIm⁺ loaded. Furthermore, density functional theory calculations were performed to study the mechanism of the CO₂ reduction.