Rational Pore Design of a Cage-like Metal-Organic Framework for Efficient C2H2/CO2 Separation

A Scalable Pore-space-partitioned Metal-organic Framework Powered by Polycatenation Strategy for Efficient Acetylene Purification

Efficient separation of acetylene (C2H2) from carbon dioxide (CO2) and ethylene (C2H4) is a significant challenge in the petrochemical industry due to their similar physicochemical properties. Pore space partition (PSP) has shown promise in enhancing gas adsorption capacity and selectivity by reducing pore size and increasing the density of guest binding sites. Herein, we firstly employ the 2D→3D polycatenation strategy to construct a PSP metal-organic framework (MOF) Ni-dcpp-bpy, incorporating functional N/O sites to enhance C2H2 purification. The polycatenated framework with optimized pore size and regularity, exhibiting significant improvements over traditional PSP MOFs by resolving the critical contradiction of balancing C2H2 uptake (98.5 cm3 g-1 at 298 K, 100 kPa) and selectivity of C2H2/CO2 (3.4), C2H2/C2H4 (5.9), and C2H2/CH4 (96.4) in a MOF. Breakthrough experiments confirm high-purity C2H4 (>99.9 %) and high C2H2 productivity from binary and ternary mixtures. Notably, Ni-dcpp-bpy exhibits excellent water stability, scalability, and regenerability after 20 cycles for separating C2H2/CO2. Theoretical calculations verify that the strong binding of C2H2 is mainly attributed to the C-H⋅⋅⋅O/N interactions between host Ni-dcpp-bpy and guest C2H2 molecules. The polycatenation strategy not only improved industrial C2H2 purification efficiency but also enriched the design diversity of customized MOFs for other gas separation applications.

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.

Enabling C2H2/CO2 Separation Under Humid Conditions with a Methylated Copper MOF

As a unique subclass of metal-organic frameworks (MOFs), MOFs with open metal site (OMS) are demonstrated efficient gas separation performance through pi complexation with unsaturated hydrocarbons. However, their practical application faces the challenge of humidity that causes structure degradation and completive binding at the OMS. In this work, the effect of linker methylation of a copper MOF (BUT-155) on the C2H2/CO2 separation performance under humid condition is evaluated. The water adsorption isotherm, adsorption kinetics, and breakthrough under dry and humid conditions are performed. The BUT-155 with methylated linker exhibits lower water uptake and adsorption kinetics under humid condition (RH = 20%), in comparison with HKUST-1. Therefore, the C2H2/CO2 separation performance of BUT-155 is much less affected by water, especially under higher gas flow rate. Moreover, the dynamic C2H2/CO2 separation performance of BUT-155 can maintain five breakthrough cycles under humid conditions (RH = 20% and RH = 80%) without obvious performance degradation.

Cu-MOFs with Rich Open Metal and F Sites for Separation of C2H2 from CO2 and CH4

Herein, we used the 4-fluoro-[1,1'-biphenyl]-3,4',5-tricarboxylic acid (H₃fbptc) ligand to design and construct a new metal-organic framework (MOF), [Cu₃(fbptc)₂(H₂O)₃]·3NMP (1), which possesses rich accessible metal sites and F functional groups in the porous walls and shows high uptake for C₂H₂ (119.3 cm³ g^-1) and significant adsorption selectivity for C₂H₂ over CH₄ (14.4) and CO₂ (3.6) at 298 K and 100 kPa. In particular, for the gas mixtures of C₂H₂-CH₄ and C₂H₂-CO₂, the MOF reveals large breakthrough time ratios (C₂H₂/CH₄ = 13, C₂H₂/CO₂ = 5.9), which are particularly prominent in dynamic breakthrough experiments, also confirming the excellent potential for the practical separation of C₂H₂ from two-component mixtures (C₂H₂-CH₄ and C₂H₂-CO₂) and even three-component mixtures (C₂H₂-CO₂-CH₄).

Boosting the C2H2/CO2 Separation Performance of Metal-Organic Frameworks through Fluorine Substitution

A pair of metal-organic frameworks (MOFs) of JXNU-15 (formulated as [Co₆(μ₃-OH)₆(BTB)₂(BPY)₃]_n, BTB^3- = benzene-1,3,5-tribenzoate and BPY = 4,4'-bipyridine) and its fluorinated JXNU-15(F) ([Co₆(μ₃-OH)₆(SFBTB)₂(BPY)₃]_n) based on the fluorous 1,3,5-tri(3,5-bifluoro-4-carboxyphenyl)benzene (SFBTB^3-) ligands were presented. The detailed comparisons of the acetylene/carbon dioxide (C₂H₂/CO₂) separation abilities between the isostructural JXNU-15(F) and JXNU-15 were presented. In comparison with the parent JXNU-15, the higher C₂H₂ uptake, larger adsorption selectivity of the C₂H₂/CO₂ (50/50) mixture, and enhanced C₂H₂/CO₂ separation performance endow JXNU-15(F) with highly efficient C₂H₂/CO₂ separation performance, which is demonstrated by singe-component gas adsorptions and dynamic gas mixture breakthrough experiments. The fluorine substituents exert the crucial effects on the enhanced C₂H₂/CO₂ separation ability of JXNU-15(F) and play the dominant role in the C₂H₂-framework interactions, as uncovered by computational simulations. This work illustrates a powerful fluorine substitution strategy for boosting C₂H₂/CO₂ separation ability for MOFs.