N-doped nanocarbon embedded in hierarchically porous metal-organic frameworks for highly efficient CO2 fixation

In Situ Pyrolysis of ZIF-67 to Construct Co2N0.67@ZIF-67 for Photocatalytic CO2 Cycloaddition Reaction

The development of heterogeneous catalysts with abundant active sites is pivotal for enhancing the efficiency of photothermal CO2 conversion. Herein, we report the construction of Co2N0.67@ZIF-67 through the in situ pyrolysis of ZIF-67 under low-temperature pyrolysis conditions. During the pyrolysis process, the crystal structure of ZIF-67 is predominantly preserved concurrently with the formation of Co2N0.67 nanoparticles (NPs) within the ZIF-67 pores. The optimal catalyst Co2N0.67@ZIF-67(450,2) not only possesses high photothermal efficiency but also can efficiently activate CO2. Benefiting from these characteristics, Co2N0.67@ZIF-67(450,2) exhibited significant catalytic activity in the photocatalytic cycloaddition of CO2 and epichlorohydrin. The yield of (chloromethyl)ethylene carbonate reached 95%, which is more than 4 times higher than that of ZIF-67 under visible light irradiation (300 W·m2 Xe lamp, 3 h). This study could offer an alternative approach to enhance the photocatalytic activity of MOFs through low-temperature pyrolysis.

Enhancement of CO2 adsorption and separation in basic ionic liquid/ZIF-8 with core-shell structure

A novel strategy was proposed to improve the performance of gas separation in nano-materials, by fabricating a core-shell structure out of the basic ionic liquid ([Emim]2[IDA]) and zeolitic imidazolate framework (ZIF-8). The [Emim]2[IDA]/ZIF-8 exhibits a remarkable CO2 adsorption capacity of 14 cm3 g-1 at 298 K and 20 kPa, the ideal selectivity of CO2/N2 is as high as 104 and CO2/CH4 is 348 at 298 K and 100 kPa, which are much higher than the CO2 adsorption capacity (4.3 cm3 g-1) and the selectivity (SCO2/N2 = 7.4, SCO2/CH4 = 2.7) of ZIF-8. This work could pave the way for designing advanced nanostructures tailored for gas separation.

Metal-Organic-Framework-Derived Bromine and Nitrogen Dual-Doped Porous Carbon for CO2 Photocycloaddition Reaction

The cycloaddition of CO2 with epoxides driven by light irradiation is an intriguing approach to preparing cyclic carbonates. However, it remains a great challenge to achieve high photocatalytic efficiency in the absence of a cocatalyst. Herein, we explored a metal-organic-framework (MOF)-templated pyrolysis strategy to prepare uniform bromine ions/nitrogen-codoped carbon materials (Br-CN) as low-cost photocatalysts for CO2 cycloaddition. The optimal catalyst Br-CN-1-550 can be used as a photocatalyst to catalyze CO2 cycloaddition, remarkably reducing the energy consumption. As a result of its benefits of high photothermal efficiency and rich nucleophilic sites (Br ions), BN-CN-1-550 affords a 9 times higher yield of 4-(chloromethyl)-1,3-dioxolan-2-one than that of the ZIF-8-derived CN under cocatalyst-free conditions and light irradiation (300 mW·cm-2 full-spectrum irradiation, 10 h). This strategy provides a cost-effective way to obtain cyclic carbonate under cocatalyst-free conditions.

Construction of Hollow Ultrasmall Co3O4 Nanoparticles Immobilized in BN for CO2 Conversion

Rational design and fabrication of metal-organic framework-derived metal oxide (MO) materials featuring a hollow structure and active support can significantly enhance their catalytic activity for specific reactions. Herein, a series of Co3O4 nanoparticles (NPs) immobilized in boron nitride (denoted as Co3O4@BN) with highly open and precisely controllable structures were constructed by an in situ self-assembly method combined with a controlled annealing process. The obtained Co3O4@BN not only possesses a hollow structure but also shows highly dispersed Co3O4 NPs and high loadings of up to 34.3 wt %. Owing to the ultrafine particle size and high dispersity, the optimized Co3O4@BN exhibits high catalytic activity for the cycloaddition of CO2 to epoxides under mild conditions (i.e., 100 °C and CO2 balloon), resulting in at least 4.5 times higher yields (99%) of styrene carbonate than that of Co3O4 synthesized by the pristine ZIF-67. This strategy sheds light on the rational design of hollow MO materials for various advanced applications.

Thermocatalytic Conversion of CO2 to Valuable Products Activated by Noble-Metal-Free Metal-Organic Frameworks

Thermocatalysis of CO2 into high valuable products is an efficient and green method for mitigating global warming and other environmental problems, of which Noble-metal-free metal-organic frameworks (MOFs) are one of the most promising heterogeneous catalysts for CO2 thermocatalysis, and many excellent researches have been published. Hence, this review focuses on the valuable products obtained from various CO2 conversion reactions catalyzed by noble-metal-free MOFs, such as cyclic carbonates, oxazolidinones, carboxylic acids, N-phenylformamide, methanol, ethanol, and methane. We classified these published references according to the types of products, and analyzed the methods for improving the catalytic efficiency of MOFs in CO2 reaction. The advantages of using noble-metal-free MOF catalysts for CO2 conversion were also discussed along the text. This review concludes with future perspectives on the challenges to be addressed and potential research directions. We believe that this review will be helpful to readers and attract more scientists to join the topic of CO2 conversion.

Opportunities from Metal Organic Frameworks to Develop Porous Carbons Catalysts Involved in Fine Chemical Synthesis

In the last decade, MOFs have been proposed as precursors of functional porous carbons with enhanced catalytic performances by comparison with other traditional carbonaceous catalysts. This area is rapidly growing mainly because of the great structural diversity of MOFs offering almost infinite possibilities. MOFs can be considered as ideal platforms to prepare porous carbons with highly dispersed metallic species or even single-metal atoms under strictly controlled thermal conditions. This review briefly summarizes synthetic strategies to prepare MOFs and MOF-derived porous carbons. The main focus relies on the application of the MOF-derived porous carbons to fine chemical synthesis. Among the most explored reactions, the oxidation and reduction reactions are highlighted, although some examples of coupling and multicomponent reactions are also presented. However, the application of this type of catalyst in the green synthesis of biologically active heterocyclic compounds through cascade reactions is still a challenge.

Integration of polypyridyl-based ionic liquids into MIL-101 for promoting CO2 conversion into cyclic carbonates under cocatalyst-free and solventless conditions

The polypyridyl-based ionic liquid-functionalized MIL-101(Cr) greatly enhanced the epoxide–CO2 cycloaddition reaction under cocatalyst-free and solventless conditions.