Thiadiazole-Linked Covalent Organic Frameworks for Efficient Separation of Propylene

Abstract

The construction of functional and robust covalent organic frameworks (COFs) for gas separation, particularly for the efficient removal of CO₂ from propylene (C₃H₆), is both significant and challenging. Herein, thiadiazole-linked COFs were reported by postsynthetic modification (PSM) of hydrazone-linked COFs with Lawesson's reagent (LR). The as-prepared thiadiazole-linked COFs not only retain porosity and crystallinity but also enhance their chemical stability. Furthermore, both thiadiazole-linked COFs demonstrate excellent C₃H₆ adsorption capacity. Notably, TDA-Ta-ODH-COF exhibits higher C₃H₆ adsorption capacity, which can separate C₃H₆ from the C₃H₆/CO₂ mixture. Dynamic separation results at 298 K and 1 bar indicate that CO₂ first breaks through the bed at 80 min/g due to the higher adsorption affinity of C₃H₆. C₃H₆ is not detected until 100 min/g. Consequently, this process yields a polymer-grade C₃H₆ output of 2.01 mmol/g. In addition, TDA-Ta-ODH-COF also has the potential to separate polymer-grade C₃H₆ from a ternary mixture of C₃H₆/CH₄/CO₂ (1/1/1). The observed adsorption disparity originates from the abundant heteroatomic sites (N, O, S) in the thiadiazole-linked COFs, which exhibit distinct adsorption affinities for C₃H₆, CH₄, and CO₂. A suitable isosteric heat of adsorption (Q_st) provides sufficient driving force for selective capture while facilitating low-cost and efficient regeneration. This work presents a facile protocol for fabricating stable and functional COFs, providing references for gas adsorption and separation applications.

Keywords

Postsynthetic modification / Covalent organic frameworks / Thiadiazole / Heteroatom / C₃H₆/CO₂/CH₄ / Dynamic separation

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