Metal-organic frameworks (MOFs) have shown great promise for CO2 capture and storage. However, the operation of chemical redox functions of framework substances and organic CO2 -trapping entities which are spatially linked together to catalyze CO2 conversion has had much less attention. Reported herein is a cobalt-containing zeolitic imidazolate framework (Co-ZIF-9) which serves as a robust MOF cocatalyst to reduce CO2 by cooperating with a ruthenium-based photosensitizer. The catalytic turnover number of Co-ZIF-9 was about 450 within 2.5 hours under mild reaction conditions, while still keeping its original reactivity during prolonged operation.

The combination of cobalt redox catalysis and carbon nitride photocatalysis to construct a cascade photoreaction system has been developed for the deoxygenative reduction of CO2 to CO with visible light. The graphitic carbon nitride has been demonstrated to function both as a capture/activation substrate of CO2 and a photocatalyst, whereas the introduced cobalt species act as reductive and oxidative promoters to accelerate charge-carrier separation and transfer kinetics. This hybrid photosystem contains inexpensive substances that synergetically catalyze CO2-to-CO conversion at mild conditions, with a high stability of catalysts. The optimization in the surface and texture structures as well as reaction conditions has been demonstrated. The results represent an important step toward artificial photosynthesis by using cost-acceptable materials.

A noble-metal-free system for photochemical reduction of CO 2 has been developed by integrating graphitic carbon nitride (g-C 3 N 4 ) with a cobalt-containing zeolitic imidazolate framework (Co-ZIF-9). g-C 3 N 4 acts as a semiconductor photocatalyst, whereas Co-ZIF-9 is a cocatalyst that facilitates the capture/concentration of CO 2 and promotes light-induced charge separation. The two materials cooperate efficiently to catalyze CO 2 -to-CO conversion upon visible light illumination under mild reaction conditions. A 13 C-labelled isotropic experiment proved that CO 2 is the carbon source of the produced CO. Even without noble metals, the system still achieved an apparent quantum yield of 0.9 percent. The system displayed high photocatalytic stability, without noticeable alterations in the chemical and crystal structures of g-C 3 N 4 and Co-ZIF-9 after the reaction.The development of semiconductor-redox systems with high efficiency for the conversion of CO 2 into C1 building blocks or fuels is not only of scientific interest but could also offer a sustainable pathway to solve energy and environmental problems. 1 Tremendous research effort has been focused on the photocatalytic reduction of CO 2 to energized molecules (i.e. CO, CH 4 , and CH 3 OH) 2 as stimulated by natural photosynthesis by which solar energy, CO 2 and water are converted into bio-compounds and dioxygen. However, it is a great challenge to activate a linear CO 2 molecule by artificial materials due to its high thermodynamic stability. 3 To fulfill the crucial mission of solar-driven CO 2 conversion, one often needs to integrate light harvesters, charge mediators, and cocatalysts into a cascade catalytic system to achieve efficient CO 2 reduction. 4 Many catalytic systems that contain noble metal catalysts 5 and/or cocatalysts 6 have been designed for the conversion of CO 2 . But, the scarcity of these noble metals limits their longterm and large-scale development. Exploring noble-metal-free systems for efficient CO 2 photofixation is therefore actively perused nowadays. Several types of transition-metal-based semiconductor catalysts such as TiO 2 , 7 ZrO 2 , 8 MgO, 9 Ga 2 O 3 , 10 ZnGa 2 O 4 11 and ZnGe 2 O 4 12 have been reported for photocatalytic reduction of CO 2 , but the activity of the reaction systems is very low, mainly due to the fast recombination of photogenerated electron-hole pairs and surface kinetic limitations. Thus, to obtain high photocatalytic efficiency, cocatalysts that are capable of developing Schottky diodes for quickly transferring the excited electrons to react with activated CO 2 are essential in photocatalytic CO 2 reduction. Transition-metal ions with multiple redox states and organic ligands can serve as excellent cocatalysts to rapidly transfer the excited electrons for the subsequent CO 2 reduction reaction, inhibiting the recombination of photoinduced electrons and holes. As a result, the multi-electron reduction of CO 2 is accelerated, especially when the process is coupled with protons. Then again, to accompli...

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The conversion of CO 2 to chemical feedstocks is of great importance, which yet requires the activation of thermodynamically-stable CO 2 by metal catalysts or metalloenzymes. Recently, the development of metal-free organocatalysts for use in CO 2 activation under ambient conditions has opened new avenues for carbon fixation chemistry. Here, we report the capture and activation of CO 2 by ionic liquids and coupling to photoredox catalysis to synthesize CO. The chemical nature of anions and the organic functional groups on the imidazolium cations of ionic liquids, together with reaction medium have been demonstrated to have remarkable effects on the activation and reduction of CO 2 . Considering almost unlimited structural variations of ionic liquids by a flexible combination of cations and anions, this photochemical pathway provides unique opportunities for carbon fixation by rationally-designed chemical systems via linking ionic liquid based materials with chromorphoric molecules in tackling the great challenges of artificial photosynthesis.C onversion of carbon dioxide (a main component of natural photosynthesis) as a renewable C1 feedstock to value-added compounds (e.g., methane, methanol, carbon monoxide, and sugar) has attracted considerable attention due to its significance in chemical industry, geopolitics and carbon recycling within the ecosystem [1][2][3][4][5][6] . In nature, the capture, concentration and conversion of atmospheric CO 2 is realized by metalloenzymes in photosynthetic organisms such as plants, algae and cyanobacteria that convert CO 2 , water and solar energy to sugars for the plant and oxygen for Earth's atmosphere. Usually, artificial conversion of extremely-inert CO 2 require its catalytic activation by transition-metal catalysts with multiple redox states and subsequently integrating to reduction reactions via multi-electron transfer coupled with protons to avoid high energy intermediates.Recent development in the field of C1 chemistry involves the emergent applications of metal-free organocatalysts, such as frustrated Lewis pairs (FLPs), carbenes, bicyclic amidines, and ionic liquids (ILs) as chemical coordination substrates for the binding and activation of CO 2 at room temperature and atmospheric pressure (Fig. 1) [7][8][9][10] . For example, FLPs were illustrated to catalyze CO 2 reduction to methanol and methane 11 . N-heterocyclic carbene (NHC) converts CO 2 to CH 3 OH via formation of zwitterionic NHCNCO 2 adducts as key intermediates in the reductive deoxygenation of CO 2 with diphenylsilane as a stoichiometic reductant 12 . Very recently, Rosen et al. has demonstrated the promoted electrochemical reduction of CO 2 to CO at overpotential of only 0.17 V by using 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid as the CO 2 coordinating substrates in water 13 .ILs are room temperature molten salts, formed by the weak combination of a large organic ion and a chargedelocalized inorganic/organic anion, with versatile structural and functional variations 14 . The scientifi...