Observation of Olefin/Paraffin Selectivity in Azo Compound and Its Application into a Metal–Organic Framework

Olefin/paraffin separation is an important and challenging issue because the two molecules have similar physicochemical properties. Although a couple of olefin adsorbents have been developed by introducing inorganic nanoparticles into metal–organic frameworks (MOFs), there has been no study on the development of an olefin adsorbent by introducing a certain organic functional group into a MOF. In this study, we posited that azo compounds could offer olefin/paraffin selectivity. We have revealed using first-principles calculations that the simplest aromatic azo compound (azobenzene, Azob) has an unusual propylene/propane selectivity due to special electrostatic interactions between Azob and propylene molecules. On the basis of this interesting discovery, we have synthesized a novel propylene adsorbent, MIL-101­(Cr)_DAA, by grafting 4,4′-diaminoazobenzene (DAA) into open metal sites in a mesoporous MIL-101­(Cr). Remarkably, MIL-101­(Cr)_DAA exhibited enhanced propylene/propane selectivity as well as considerably higher propylene heat of adsorption compared to pristine MIL-101­(Cr) while maintaining the high working capacity of MIL-101­(Cr). This clearly indicates that azo compounds when introduced into MOFs can provide propylene selectivity. Moreover, MIL-101­(Cr)_DAA showed good C₃H₆/C₃H₈ separation and easy regeneration performances from packed-bed breakthrough experiments and retained its propylene adsorption capacity even after exposure to air for 12 h. As far as we know, this is the first study that improves the olefin selectivity of MOF by postsynthetically introducing an organic functional group

Synthesis of a Zr-Based Metal–Organic Framework with Spirobifluorenetetrabenzoic Acid for the Effective Removal of Nerve Agent Simulants

A new microporous Zr­(IV)-based metal–organic framework (MOF) containing 4,4′,4″,4‴-(9,9′-spirobi­[fluorene]-2,2′,7,7′-tetrayl)­tetrabenzoic acid (Spirof-MOF) was synthesized, characterized, and size-controlled for the adsorption and decomposition of a nerve agent simulant, dimethyl 4-nitrophenylphosphate (DMNP). Spirof-MOF showed a hydrolysis half-life (<i>t</i>_1/2) of 7.5 min to DMNP, which was confirmed by using in situ ³¹P NMR spectroscopy. Additionally, size-controlled Spirof-MOFb (∼1 μm) exhibited a half-life of 1.8 min and 99% removal within 18 min for DMNP. The results show that Spirof-MOF is a new active material in removing nerve agent simulants by adsorption and hydrolytic decomposition