Efficient capture of trace benzene vapor by metal–organic frameworks modified with macrocyclic pyridyl ligands

The capture of trace benzene vapor is an important and huge challenge due to its serious toxicity. Physisorbents usually exhibit weak interactions especially in the presence of trace concentrations, thus possessing poor removal performance. Herein, an efficient post-synthetic modification strategy with various mono-, bi-, and tri-pyridyl derivative ligands was performed on the parent [Fe₃(μ₃-O)(OH)(H₂O)₂(pet)] (NU-1500(Fe), H₆pet = peripherally extended triptycene, 4,4',4'',4''',4''',4'''-(9,10-dihydro-9,10-[1,2]benzenoanthracene-2,3,6,7,14,15-hexayl)hexabenzoic acid) with large hexagonal pores (14 × 19 Ų) and modifiable metal sites. Remarkably, these MOFs can regulate the performance of trace adsorption of benzene. Among them, the tri-pyridyl ligand modified [Fe₃(μ₃-O)(pet)(tph)] (WYU-107, Htph = 2,5,8-tri-(4-pyridyl)-1,3,4,6,7,9-hexaazaphenalene) reaches an uptake of 6.21 mmol g^-1 at 298 K and <i>P</i>/<i>P</i> ₀ = 0.01 by virtue of the significant interactions between the pore partitioned host-framework and benzene molecules, which shows a capture performance exceeding that of most of the reported porous materials. At the same time, breakthrough experiments revealed that WYU-107 can capture trace benzene in the air, and <i>in situ</i> variable-pressure PXRD indicates the reversible deformation behavior during the adsorption process. Theoretical calculations and <i>in situ</i> single-crystal structure reveal that the significant interactions are closely related to the insertion of the functional tph ligand, facilitating the capture of benzene vapor at trace levels.