Enhancing Perfluorinated electron specialty gases separation selectivity in ultra-microporous metal organic framework

Purification of Xe and SF6 through Adaptive Contractions in a Flexible Metal-Organic Framework

Overcoming the trade-off effects between adsorption capacity, adsorption selectivity, and adsorption enthalpy of an adsorbent is very important but remains a huge challenge. Here, we report a flexible metal-organic framework (FJI-H36); it can selectively adsorb Xe from Xe/Kr mixtures with high adsorption capacity but very low adsorption enthalpy. Structural analyses show that such excellent adsorption performances come from the adaptive contraction of the flexible framework; pore shrinkage can enhance the interactions between adsorbed Xe and the framework and offset some of the adsorption heats. For SF6/N2 mixtures, FJI-H36 can also enhance the adsorption performance of SF6 through adaptive contraction, resulting in both high adsorption selectivity and low adsorption enthalpy. This not only provides a new adsorbent for the purification of Xe/Kr/SF6 but also offers a potential solution to overcome the trade-offs among adsorption capacity, adsorption selectivity, and adsorption enthalpy of a specific adsorbent.

A Flexible Interpenetrated Diamondoid Metal-Organic Framework with Aromatic-Enriched Channels as a Preconcentrator for the Detection of Fluorinated Anesthetics

Flexible metal-organic frameworks (MOFs) are dynamic materials that combine long-range structural order with reversible stimulus-responsive phase transitions. In this study, we report the synthesis and characterization of two isoreticular flexible MOFs, TPPM-CPW(Me) and TPPM-CPW(Ph), constructed by combining the ligand tetra-4-(4-pyridyl)phenylmethane (TPPM) with specific Cu(II) paddle-wheel (CPW) secondary building units (SBUs). These MOFs exhibit reversible transitions between open- and closed-pore forms triggered by external stimuli, such as temperature- and pressure-induced guest removal and uptake. The stability of these frameworks is influenced by the residual equatorial groups on the Cu(II) SBUs, with phenyl-functionalized TPPM-CPW(Ph) displaying dynamic behavior characteristic of third-generation soft porous crystals. Notably, TPPM-CPW(Ph) exhibited high adsorption affinity toward fluorinated guests, including SF6 and volatile anesthetics (VAs) such as desflurane and sevoflurane. This material, when used in solid-phase microextraction (SPME) as fiber coating for the preconcentration of these VAs in air, outperformed commercial CAR/PDMS fibers, underscoring the potential of these versatile flexible MOFs in addressing environmental challenges associated with the use of volatile fluorinated compounds.

Molecular Mechanism Behind the Capture of Fluorinated Gases by Metal-Organic Frameworks

Fluorinated gases (F-gases) play a vital role in the chemical industry and in the fields of air conditioning, refrigeration, health care, and organic synthesis. However, the direct emission of waste gases containing F-gases into the atmosphere contributes to greenhouse effects and generates toxic substances. Developing porous materials for the energy-efficient capture, separation, and recovery of F-gases is highly desired. Recently, as a highly designable porous adsorbents, metal-organic frameworks (MOFs) exhibit excellent selective sorption performance toward F-gases, especially for the recognition and separation of different F-gases with highly similar properties, showing their great potential in F-gases control and recovery. In this review, we discuss the capture and separation of F-gases and their azeotropic, near-azeotropic, and isomeric mixtures in various application scenarios by MOFs, specifically classify and analyze molecular interaction between F-gases and MOFs, and interpret the mechanisms underlying their high performance regarding both adsorption capacity and selectivity, providing a repertoire for future materials design. Challenges faced in the transformation research roadmap of MOFs adsorbent separation technologies toward F-gases are also discussed, and areas for future research endeavors are highlighted.

Metal-Organic Framework-Based NF3 Nanotrap for the Separation of NF3 and CF4

As an electronic specialty gas, nitrogen trifluoride (NF3) has been widely used in the semiconductor, photovoltaic, and display industries. However, NF3 in industrial settings is typically mixed with CF4, and the distillation method commonly used for their separation consumes significant energy. Herein, we propose a novel NF3 nanoadsorber featuring relatively proximal unsaturated metal sites. The potential field overlap between the two unsaturated metal centers creates an NF3-affinitive environment. The adsorption mechanism of NF3 molecules in the metal-organic frameworks (MOFs) was investigated through density functional theory (DFT) optimization. The results from ideal adsorbed solution theory (IAST) calculations and breakthrough experiments reveal that the MOF-based NF3 nanotrap possesses the highest adsorption capacity and excellent NF3/CF4 selectivity among the physically adsorptive materials reported to date. This work presents a novel solution for the separation and purification of NF3, contributing to the field of gas separation technology.

Destructive Adsorption of Nitrogen Trifluoride (NF3) Using M-MOF-74 with Open Metal Sites

Using solid adsorbents for the destructive sorption of nitrogen trifluoride (NF3) presents a potential solution to its dual challenges as a potent greenhouse gas and hazardous compound in microelectronics. In this study, a series of MOFs (M-MOF-74, M = Mg, Co, Ni, Zn) with open metal sites (OMSs) are utilized for NF3 adsorption. By employing single-component adsorption isotherms and the ideal adsorbed solution theory (IAST) selectivity calculations, the adsorption performance of various adsorbents is evaluated. The results indicate that Mg, Co, and Ni-MOF-74 exhibit high adsorption capacities for NF3, while Zn-MOF-74 shows a lower adsorption capacity, likely due to the weaker Lewis acidity of Zn2+. Experimental findings from PXRD and gas adsorption studies indicate structural pore alteration in the MOF-74 series following NF3 gas adsorption. Theoretical computational analyses reveal that the MOF-74 series has a higher adsorption affinity for NF3 compared to N2. This research provides insights into the use of efficient MOF sorbents for the destructive adsorption of NF3.

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.

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.

High throughput screening of pure silica zeolites for CF4 capture from electronics industry gas

The capture and separation of CF4 from CF4/N2 mixture gas is a crucial issue in the electronics industry, as CF4 is a commonly used etching gas and the ratio of CF4 to N2 directly affects process efficiency. Utilizing high-throughput computational screening techniques and grand canonical Monte Carlo (GCMC) simulations, we comprehensively screened and assessed 247 types of pure silicon zeolite materials to determine their adsorption and separation performance for CF4/N2 mixtures. Based on screening, the relationships between the structural parameters and adsorption and separation properties were meticulously investigated. Four indicators including adsorption selectivity, working capacity, adsorbent performance score (APS), and regenerability (R%) were used to evaluate the performance of adsorbents. Based on the evaluation, we selected the top three best-performing zeolite structures for vacuum swing adsorption (LEV, AWW and ESV) and pressure swing adsorption (AVL, ZON, and ERI) processes respectively. Also, we studied the preferable adsorption sites of CF4 and N2 in the selected zeolite structures through centroid density distributions at the molecule level. We expect the study may provide some valuable guidance for subsequent experimental investigations on adsorption and separation of CF4/N2.

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.

Absolute CO2 /Xenon Separation in Ultramicropore MOF for Anesthetic Gases Regeneration

Xe is an ideal anesthetic gas, but it has not been widely used in practice due to its high cost and low output. Closed-circuit Xe recovery and recycling is an economically viable method to ensure adequate supply in medical use. Herein, we design an innovative way to recover Xe by using a stable fluorinated metal-organic framework (MOF) NbOFFIVE-1-Ni to eliminate CO2 from moist exhaled anesthetic gases. Unlike other Xe recovery MOFs with low Xe/CO2 selectivity (less than 10), NbOFFIVE-1-Ni could achieve absolute molecular sieve separation of CO2 /Xe with excellent CO2 selectivity (825). Mixed-gas breakthrough experiments assert the potential of NbOFFIVE-1-Ni as a molecular sieve adsorbent for the effective and energy-efficient removal of carbon dioxide with 99.16 % Xe recovery. Absolute CO2 /Xe separation in NbOFFIVE-1-Ni makes closed-circuit Xe recovery and recycling can be easily realized, demonstrating the potential of NbOFFIVE-1-Ni for important anesthetic gas regeneration under ambient conditions.

Polypyrene Porous Organic Framework for Efficiently Capturing Electron Specialty Gases

The polypyrene polymer with an extended π-conjugated skeleton is attractive for perfluorinated electron specialty gas (F-gas) capture as the high electronegativity of fluorine atoms makes F-gases strongly electronegative gases. Herein, a polypyrene porous organic framework (termed as Ppy-POF) with an extended π-conjugated structure and excellent acid resistance was constructed. Systematic studies have shown that the abundant π-conjugated structures and gradient electric field distribution in Ppy-POF can endow it exceptional adsorption selectivity for high polarizable F-gases and xenon (Xe), which has been collaboratively confirmed by single-component gas adsorption experiments, time-dependent adsorption rate tests, dynamic breakthrough experiments, etc. Electrostatic potential distribution and charge density difference based on Grand Canonical Monte Carlo simulations and density functional theory calculations demonstrate that the selective adsorption of F-gases and Xe in Ppy-POF is attributed to the strong charge-transfer effect and polarization effect between Ppy-POF and gases. These results manifest that the POF with an extended π-conjugated structure and gradient electric field distribution has great potential in efficiently capturing electron specialty gases.