A monolithic composite based on zeolite-like metal-organic framework@divinylbenzene polymer separates azeotropic fluorocarbon mixture efficiently

Organic monolithic columns are mainly used to separate macromolecules; however, many attempts to extend their performance toward small molecules were examined by incorporating micro-and nanopar-ticles. The incorporation technique enabled utilizing organic monoliths in gas chromatography (GC) for small molecules, which are still scarce. Here, we prepared a composite matrix of capillary monolithic columns of a zeolite-like metal-organic framework with a sodalite topology (sod-ZMOF) and Divinylben-zene polymer (DVB) for GC separations under 0.5 MPa. Relatively short DVB monolithic columns (18 cm long x 0.25 mm i.d.) incorporated with a tiny amount of sod-ZMOF nanoparticles (0.7 and 1.17 wt%) with an average particle size of 225 nm were successfully fabricated and used to separate linear alkanes and polar probes mixtures with increasing resolution up to 3.7 and 5.1 times, respectively, compared to a blank DVB monolithic column. A high-performance separation of linear alkanes series mixture (methane to decane) was exhibited in less than 2 min. McReynolds constants revealed that sod-ZMOF provided the composite monolith with a nonpolar character yielding a negative average polarity value smaller than the standard squalene column. An Excellent retention time of pentane and octane day-to-day reproducibility was achieved during 16 days and over more than 500 runs with RSD% of 2.25% and 3.3% using a compos-ite monolithic column with 5 mg mL -1 sod-ZMOF (5-ZMOF@DVB). In addition, a qualitative determina-tion of the gas mixture content of three commercially available Lighter gas cartridges was performed via the 5-ZMOF@DVB column. Finally, successfully separating an azeotropic freon mixture of difluoromethane (R-32) and pentafluoroethane (R-125) was achieved with a selectivity of up to 4.84. A further thermody-namic study related the preferential adsorption of R-125 to entropic factors rather than enthalpic while trapping inside ZMOF pores. This work sheds light on utilizing the infinite diversity of MOFs and combin-ing their properties with high permeability and easily fabricated organic monoliths for GC separations of light molecules and gasses. Furthermore, the study highlights the role of GC as an easy and fast approach for the preliminary evaluation of the separation efficiency of porous polymers. (c) 2023 Elsevier B.V. All rights reserved.

Automated summary

In this study, a composite matrix of capillary monolithic columns was successfully fabricated for gas chromatography separations. It showed high efficiency in separating linear alkanes and polar probes mixtures, with excellent retention time and reproducibility. The study highlights the role of MOFs combined with organic monoliths in gas chromatography separations and emphasizes the use of GC as a fast approach for evaluating porous polymer separation efficiency.