Solar-driven conversion of carbon dioxide over nanostructured metal-based catalysts in alternative approaches: Fundamental mechanisms and recent progress.

Solar-driven carbon dioxide (CO2) conversion has gained tremendous attention as a prominent strategy to simultaneously reduce the atmospheric CO2 concentration and convert solar energy into solar fuels in the form of chemical bonds. Numerous efforts have been devoted to diverse photo-driven processes for CO2 conversion, which utilized a multidisciplinary strategy. Among them, the architecture of nanostructured metal-based catalysts is emerging as an eminent solution for the design of catalysts of this field. In this work, we first provide fundamental mechanisms of photochemical, photoelectrochemical, photothermal, and photobio(electro)chemical CO2 reduction processes to achieve an in-deep understanding of vital aspects. Importantly, the recent progress in the catalyst design for each reaction system is discussed and highlighted. Based on these analyses, an overview of photo-driven CO2 reduction on metal-based catalysts for solar fuel production is also spotlighted. Finally, we analyze challenges and prospects for the strategic direction of developments in the field.

A Series of Metal-Organic Frameworks for Selective CO2 Capture and Catalytic Oxidative Carboxylation of Olefins.

Three new lanthanide-based metal-organic frameworks (Ln-MOFs), namely MOF-590, -591, and -592 constructed from a tetratopic linker, benzoimidephenanthroline tetracarboxylic acid (H4BIPA-TC), were synthesized under solvothermal conditions and fully characterized. All of the new MOFs exhibit three-dimensional frameworks, which adopt unprecedented topologies in MOF field. Gas adsorption measurements of MOF-591 and -592 revealed good adsorption of CO2 (low pressure, at room temperature) and moderate CO2 selectivity over N2 and CH4. Consequently, breakthrough experiments illustrated the separation of CO2 from binary mixture of CO2 and N2 with the use of MOF-592. Accordingly, MOF-592 revealed the selective CO2 capture effectively without any loss in performance after three cycles. Moreover, MOF-590, -591, and -592 showed to be catalytically active in the oxidative carboxylation of styrene and CO2 for a one-pot synthesis of styrene carbonate under mild conditions (1 atm CO2, 80 °C, and without solvent). Among the new materials, MOF-590 revealed a remarkable efficiency with exceptional conversion (96%), selectivity (95%), and yield (91%).

Mixed-Metal Zeolitic Imidazolate Frameworks and their Selective Capture of Wet Carbon Dioxide over Methane.

A presynthesized, square planar copper imidazole complex, [Cu(imidazole)4](NO3)2, was utilized as a precursor in the synthesis of a new series of zeolitic imidazolate frameworks, termed ZIF-202, -203, and -204. The structures of all three members were solved by single-crystal X-ray diffraction analysis, which revealed ZIF-203 and -204 having successfully integrated square planar units within the backbones of their respective frameworks. As a result of this unit, the structures of both ZIF-203 and -204 were found to adopt unprecedented three-dimensional nets, namely, ntn and thl, respectively. One member of this series, ZIF-204, was demonstrated to be highly porous, exhibit exceptional stability in water, and selectively capture CO2 over CH4 under both dry and wet conditions without any loss in performance over three cycles. Remarkably, the regeneration of ZIF-204 was performed under the mild conditions of flowing a pure N2 gas through the material at ambient temperature.

Synthesis and Selective CO2 Capture Properties of a Series of Hexatopic Linker-Based Metal-Organic Frameworks.

Four crystalline, porous metal-organic frameworks (MOFs), based on a new hexatopic linker, 1',2',3',4',5',6'-hexakis(4-carboxyphenyl)benzene (H6CPB), were synthesized and fully characterized. Interestingly, two members of this series exhibited new topologies, namely, htp and hhp, which were previously unseen in MOF chemistry. Gas adsorption measurements revealed that all members exhibited high CO2 selectivity over N2 and CH4. Accordingly, breakthrough measurements were performed on a representative example, in which the effective separation of CO2 from binary mixtures containing either N2 or CH4 was demonstrated without any loss in performance over three consecutive cycles.

Iodine-mediated formal [3 + 2] annulation for synthesis of furocoumarin from oxime esters.

A novel synthesis of furocoumarins was developed by a reaction between oxime esters and 4-hydroxycoumarins. The reaction was proposed to undergo radical mechanism mediated by iodine, a cheap and common laboratory reagent. Mechanistic studies showed the key for the successful transformation was the presence of α-iodoimine intermediate which facilitated the ring-closing step. The developed conditions produced good functional group tolerance with a wide range of high-profile furocoumarin product. The potential for this strategy to be applied in other syntheses of heterocyclic compounds is highly achievable.

A Cerium-Containing Metal-Organic Framework: Synthesis and Heterogeneous Catalytic Activity toward Fenton-Like Reactions.

A cerium-based metal-organic framework, namely MOF-589, was synthesized using benzoimidephenanthroline tetracarboxylic acid (H4 BIPA-TC) as an organic linker. Full characterization including single-crystal and powder X-ray diffraction analysis, thermogravimetrical analysis, scanning electron microscopy, and N2 adsorption measurements at low pressure and 77 K were carried out. The material was employed as an efficient heterogeneous catalyst for decomposition of methylene blue (MB) dye (40 ppm) in the presence of H2 O2 in 15 minutes. Interestingly, comparison studies showed that the activity of MOF 589 was higher than that of other iron-based heterogeneous and cerium-based catalysts. Further experiments to clarify the MOF 589 activity indicated that the BIPA-TC linker might have an important impact through a cooperative effect on the metal cluster. Control studies confirmed that the presence of catalyst was necessary for the reaction to occur and the catalyst recyclability. In particular, catalysis from leached cerium in the reaction filtrate is unlikely and the solid material could be reused at least eight times without a remarkable loss in activity.

A new iron-based metal-organic framework with enhancing catalysis activity for benzene hydroxylation.

A new Fe-based metal-organic framework (MOF), termed Fe-TBAPy Fe2(OH)2(TBAPy)·4.4H2O, was solvothermally synthesized. Structural analysis revealed that Fe-TBAPy is built from [Fe(OH)(CO2)2]∞ rod-shaped SBUs (SBUs = secondary building units) and 1,3,6,8-tetrakis(p-benzoate)pyrene (TBAPy4-) linker to form the frz topological structure highlighted by 7 Å channels and 3.4 Å narrow pores sandwiching between the pyrene cores of TBAPy4-. Consequently, Fe-TBAPy was used as a recyclable heterogeneous catalyst for benzene hydroxylation. Remarkably, the catalysis reaction resulted in high phenol yield and selectivity of 64.5% and 92.9%, respectively, which are higher than that of the other Fe-based MOFs and comparable with those of the best-performing heterogeneous catalysts for benzene hydroxylation. This finding demonstrated the potential for the design of MOFs with enhancing catalysis activity for benzene hydroxylation.

New Metal-Organic Frameworks for Chemical Fixation of CO2.

A novel series of two zirconium- and one indium-based metal-organic frameworks (MOFs), namely, MOF-892, MOF-893, and MOF-894, constructed from the hexatopic linker, 1',2',3',4',5',6'-hexakis(4-carboxyphenyl)benzene, were synthesized and fully characterized. MOF-892 and MOF-893 are two new exemplars of materials with topologies previously unseen in the important family of zirconium MOFs. MOF-892, MOF-893, and MOF-894 exhibit efficient heterogeneous catalytic activity for the cycloaddition of CO2, resulting in a cyclic organic carbonate formation with high conversion, selectivity, and yield under mild conditions (1 atm CO2, 80 °C, and solvent-free). Because of the structural features provided by their building units, MOF-892 and MOF-893 are replete with accessible Lewis and Brønsted acid sites located at the metal clusters and the non-coordinating carboxylic groups of the linkers, respectively, which is found to promote the catalytic CO2 cycloaddition reaction. As a proof-of-concept, MOF-892 exhibits high catalytic activity in the one-pot synthesis of styrene carbonate from styrene and CO2 without preliminary synthesis and isolation of styrene oxide.