Scalable Synthesis of Robust MOF for Challenging Ethylene Purification and Propylene Recovery with Record Productivity

Ethylene (C2H4) purification and propylene (C3H6) recovery are highly relevant in polymer synthesis, yet developing physisorbents for these industrial separation faces the challenges of merging easy scalability, economic feasibility, high moisture stability with great separation efficiency. Herein, we reported a robust and scalable MOF (MAC-4) for simultaneous recovery of C3H6 and C2H4. Through creating nonpolar pores decorated by accessible N/O sites, MAC-4 displays top-tier uptakes and selectivities for C2H6 and C3H6 over C2H4 at ambient conditions. Molecular modelling combined with infrared spectroscopy revealed that C2H6 and C3H6 molecules were trapped in the framework with stronger contacts relative to C2H4. Breakthrough experiments demonstrated exceptional separation performance for binary C2H6/C2H4 and C3H6/C2H4 as well as ternary C3H6/C2H6/C2H4 mixtures, simultaneously affording record productivities of 27.4 and 36.2 L kg-1 for high-purity C2H4 (≥99.9 %) and C3H6 (≥99.5 %). MAC-4 was facilely prepared at deckgram-scale under reflux condition within 3 hours, making it as a smart MOF to address challenging gas separations.

Mixed-Linker Isoreticular Zn(II) Metal-Organic Frameworks as Brønsted Acid-Base Bifunctional Catalysts for Knoevenagel Condensation Reactions

Multicomponent metal-organic frameworks (MOFs) have received an increasing amount of attention due to their potential to produce new topologies, pore metrics, and functionalities compared to MOFs with a single metal cluster and one organic linker. Herein, five isoreticular Zn MOFs were obtained by mixing two types of linear ditopic linkers in a one-pot solvothermal synthesis. Interestingly, in the resulting Zn MOFs a six-connected cyclic trinuclear Zn(II) cluster and an eight-connected linear trinuclear Zn(II) cluster coexist, leading to an uncommon (6,8)-connected network. Catalytic activities toward the solvent-free Knoevenagel reactions were observed for all of these MOFs. Further experimental and computational studies suggest that they are Brønsted acid-base bifunctional catalysts. Through chemical modifications of dicarboxylate ligands, including their aromatic backbones and substituents, we have successfully implemented reticular chemistry for the modulations of pore sizes, surface areas, and catalytic performances in a series of four-component isoreticular MOFs.

Selective Adsorption-Based Separation of Flue Gas and Natural Gas in Zirconium Metal-Organic Frameworks Nanocrystals

Carbon capture from flue gas and natural gas offers a green path to construct a net-zero emissions economic system. Selective adsorption-based gas separation by employing metal-organic frameworks (MOFs) is regarded as a promising technology due to the advantages of simple processing, easy regeneration and high efficiency. We synthesized two Zirconium MOFs (UiO-66 and UiO-66-NH₂) nanocrystals for selective capture and further removal of CO₂ from flue gas and natural gas. In particular, UiO-66-NH₂ nanocrystals have a smaller grain size, a large amount of defects, and pending –NH₂ groups inside their pores which display effective CO₂ selective adsorption abilities over CH₄ and N₂ with the theoretical separation factors of 20 and 7. This breakthrough experiment further verified the selective adsorption-based separation process of natural gas and flue gas. In one further step, we used the Monte Carlo simulation to investigate the optimized adsorption sites and energy of CO₂, N₂ and CH₄ molecules in the gas mixture. The significantly large adsorption energy of CO₂ (0.32 eV) over N₂ (0.19 eV) and N₂ (0.2 eV) may help us to reveal the selective adsorption mechanism.

CO2 adsorption of three isostructural metal-organic frameworks depending on the incorporated highly polarized heterocyclic moieties

A systematic investigation of CO2 adsorption behavior in three metal-organic frameworks was executed. The three MOFs adopted the same NbO-type structure, except that the organic ligands were grafted with different highly polarized heterocyclic moieties, namely, oxadiazole, thiadiazole, and selenadiazole, respectively. After activation, the three MOF materials, ZJNU-41a showed different surface areas and pore volumes depending on the incorporated heterocyclic rings attached to the organic ligands as well as the MOF's stabilities. Among the three MOF materials, exhibited an impressive CO2 uptake capacity of 97.4 cm(3) (STP) g(-1) at 298 K and 1 atm, which is comparable and even superior to those reported in NbO-type MOFs. In particular, when the molecular dipole of the attached heterocyclic moieties increases, the CO2 uptake also increases, which was further supported by comprehensive quantum chemical calculations. This work demonstrates that the introduction of highly polarized heterocyclic functional groups into frameworks is a promising approach to target porous metal-organic framework materials with improved CO2 adsorption performance.