A nickel-based metal-organic framework for efficient SF6/N2 separation with record SF6 uptake and SF6/N2 selectivity

Fluorine Incorporation for Enhanced Gas Separation Performance in Porous Organic Polymers: Investigating Reaction Pathways and Pore Structure Control

The precise control of pore structures in porous organic polymer (POP) materials is of paramount importance in addressing a wide range of challenges associated with gas separation processes. In this study, we present a novel approach to optimize the gas separation performance of POPs through the introduction of fluorine groups and figure out an important factor of reaction decision that whether the AlCl3-catalyzed polymerization is Scholl reaction or Friedel-Crafts alkylation. In the chloroform system, the steric hindrance of function groups could make direct coupling between the benzene rings difficult, which would lead to part solvent knitting (Friedel-Crafts alkylation) instead. The fluorinated polymers show enhanced surface area and pore size characteristics. Notably, the fluorinated polymers exhibited significantly improved adsorption and separation performance for SF6, as evidenced by an ideal adsorbed solution theory selectivity (SF6/N2, v: v = 50:50, 273 K) increase of 75.0, 668.8, and 502.8% compared to the nonfluorinated POPs. These findings highlight the potential of fluorination as a strategy for tailoring the properties of POP materials for advanced gas separation applications.

Pore Environmental Modification by Amino Groups in Robust Microporous MOFs for SF6 Capturing and SF6/N2 Separation

Capturing and separating the greenhouse gas SF6 from nitrogen N2 have significant greenhouse mitigation potential and economic benefits. We used a pore engineering strategy to manipulate the pore environment of the metal-organic framework (MOF) by incorporating organic functional groups (-NH2). This resulted in an enhanced adsorption of SF6 and separation of the SF6/N2 mixture in the MOF. The introduction of amino (-NH2) groups into YTU-29 resulted in a reduction of the Brunauer-Emmett-Teller surface but an increase in interactions with SF6 within the confined pores. Water-stable YTU-29-NH2 showed a significantly higher SF6 uptake (95.5 cm3/g) than YTU-29 (77.4 cm3/g). The results of the breakthrough experiments show that YTU-29-NH2 has a significantly improved separation performance for SF6/N2 mixtures, with a high SF6 capture of 0.88 mmol/g compared to 0.56 mmol/g by YTU-29. This improvement is due to the suitable pore confinement and accessible -NH2 groups on pore surfaces. Considering its excellent regeneration ability and cycling performance, ultrastable YTU-29-NH2 demonstrates great potential for SF6 capturing and SF6/N2 separation.

Recovery of High-Purity SF6 from Humid SF6/N2 Mixture within a Co(II)-Pyrazolate Framework

Sulfur hexafluoride (SF6) is extensively employed in the power industry. However, its emissions significantly contribute to the greenhouse effect. The direct recovery of high purity SF6 from industrial waste gases would benefit its sustainable use, yet this represents a considerable challenge. Herein, we report the enrichment of SF6 from SF6/N2 mixtures via adsorptive separation in a stable Co(II)-pyrazolate MOF BUT-53 (BUT: Beijing University of Technology), which features dynamic molecular traps. BUT-53 exhibits an excellent SF6 adsorption uptake of 2.82 mmol/g at 0.1 bar and 298 K, as well as an unprecedented SF6/N2 (10:90) selectivity of 2485. Besides, the remarkable SF6/N2 selectivity of BUT-53 enables recovery of high purity (>99.9%) SF6 from a low concentration (10%) mixture through a breakthrough experiment. The excellent SF6/N2 separation efficiency was also well maintained under humid conditions (RH = 90%) over multiple cycles. Molecular simulation, single-crystal diffraction, and adsorption kinetics studies elucidate the associated adsorption mechanism and water tolerance.

Efficient Removal of Greenhouse Gases: Machine Learning-Assisted Exploration of Metal-Organic Framework Space

Global warming is a crisis that humanity must face together. With greenhouse gases (GHGs) as the main factor causing global warming, the adoption of relevant processes to eliminate them is essential. With the advantages of high specific surface area, large pore volume, and tunable synthesis, metal-organic frameworks (MOFs) have attracted much attention in GHG storage, adsorption, separation, and catalysis. However, as the pool of MOFs expands rapidly with new syntheses and discoveries, finding a suitable MOF for a particular application is highly challenging. In this regard, high-throughput computational screening is considered the most effective research method for screening a large number of materials to discover high-performance target MOFs. Typically, high-throughput computational screening generates voluminous and multidimensional data, which is well suited for machine learning (ML) training to improve the screening efficiency and explore the relationships between the multidimensional data in depth. This Review summarizes the general process and common methods for using ML to screen MOFs in the field of GHG removal. It also addresses the challenges faced by ML in exploring the MOF space and potential directions for the future development of ML for MOF screening. This aims to enhance the understanding of the integration of ML and MOFs in various fields and broaden the application and development ideas of MOFs.

Construction of Hierarchical Porous UiO-66-Br2@PS/DVB-Packed Columns by High Internal Phase Emulsion Strategy for Enhanced Separation of CF4/N2 and SF6/N2

Recovery and separation of anthropogenic emissions of electronic specialty gases (F-gases, such as CF4 and SF6) from the semiconductor sector are of critical importance. In this work, the hierarchical porous UiO-66-Br2@PS/DVB-packed column was constructed by a high internal phase emulsions strategy. UiO-66-Br2@PS/DVB exhibits a superior selectivity of CF4/N2 (2.67) and SF6/N2 (3.34) predicted by the IAST due to the diffusion limitation in the micropore and the gas-framework affinity. Especially, UiO-66-Br2@PS/DVB showed significant CF4 and SF6 retention and enabled the successful separation of CF4/N2 and SF6/N2 with a resolution of 2.37 and 8.89, respectively, when used as a packed column in gas chromatography. Compared with the Porapak Q column, the HETP of the UiO-66-Br2@PS/DVB-packed column decreased and showed good reproducibility. This research not only offers a convenient method for fabricating a hierarchical porous MOF-packed column but also showcases the prospective utilization of MOFs for the separation of the F-gas/N2 mixture.

A two-dimensional metal-organic framework assembled from scandium-based cages for the selective capture of sulfur hexafluoride

Herein, we report the synthesis of a two-dimensional metal-organic framework (MOF), assembled from octahedral metal-organic cages featuring phenanthroline-based carboxylate linkers and μ3-oxo-centered trinuclear Sc(III) inorganic building blocks. We study the performance of this MOF towards the capture of sulfur hexafluoride (SF6). On account of its structural features and porous nature, this MOF displays an SF6 uptake capacity of 0.92 mmol g-1 at 0.1 bar and an isosteric heat of adsorption of about 30.7 kJ mol-1 for SF6, illustrating its potential application for the selective capture of SF6 from N2. In addition, we study the adsorptive binding mechanism of SF6 and N2 inside this MOF via molecular simulations.

Non-CO2 greenhouse gas separation using advanced porous materials

Global warming has become a growing concern over decades, prompting numerous research endeavours to reduce the carbon dioxide (CO2) emission, the major greenhouse gas (GHG). However, the contribution of other non-CO2 GHGs including methane (CH4), nitrous oxide (N2O), fluorocarbons, perfluorinated gases, etc. should not be overlooked, due to their high global warming potential and environmental hazards. In order to reduce the emission of non-CO2 GHGs, advanced separation technologies with high efficiency and low energy consumption such as adsorptive separation or membrane separation are highly desirable. Advanced porous materials (APMs) including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs), porous organic polymers (POPs), etc. have been developed to boost the adsorptive and membrane separation, due to their tunable pore structure and surface functionality. This review summarizes the progress of APM adsorbents and membranes for non-CO2 GHG separation. The material design and fabrication strategies, along with the molecular-level separation mechanisms are discussed. Besides, the state-of-the-art separation performance and challenges of various APM materials towards each type of non-CO2 GHG are analyzed, offering insightful guidance for future research. Moreover, practical industrial challenges and opportunities from the aspect of engineering are also discussed, to facilitate the industrial implementation of APMs for non-CO2 GHG separation.