pH-Stable Eu- and Tb-organic-frameworks mediated by an ionic liquid for the aqueous-phase detection of 2,4,6-trinitrophenol (TNP)

Abstract

Two pH-stable luminescent metal–organic frameworks (LMOFs), {[Ln₂(L)₂(OH)(HCOO)]·[H₂O]}_n (Ln = Eu 1, Tb 2), based on a new π-conjugated organic building block involving both carboxylate and terpyridine groups were rationally synthesized under a combination of hydro/solvothermal and ionothermal conditions (H₂L = 4′-(4-(3,5-dicarboxylphenoxy)phenyl)-4,2′:6′,4′′-terpyridine). 1 and 2 are isostructural and feature noninterpenetrated open 3D condensed frameworks constructed by rod-shaped lanthanide-carboxylate building units. Their excellent water-stability and pH-stability allow them to be used in aquatic systems. 1 and 2 both exhibit selective and sensitive aqueous phase detection of the well-known nitroaromatic explosive environmental pollutant 2,4,6-trinitrophenol (TNP), which is highly desirable for practical applications. The presence of a free pyridine group on the LMOF particle surface was strategically utilized for the purpose of exclusive TNP-sensing.