A multi-responsive chemosensor for highly sensitive and selective detection of Fe3+, Cu2+, Cr2O72− and nitrobenzene based on a luminescent lanthanide metal–organic framework

Abstract

Excessive release of some hazardous chemicals, such as Fe³⁺, Cu²⁺, Cr₂O₇²⁻ and nitrobenzene, may endanger public health and the environment; therefore, targeted effective sensing strategies are important. In this report, a series of lanthanide-based metal–organic frameworks (Ln-MOFs), namely {[Ln(dpc)(2H₂O)]·(Hbibp)_0.5}_n (H₄dpc = 2-(3′,4′-dicarboxylphenoxy) isophthalic acid, bibp = 4,4′-bis(imidazolyl) biphenyl, for I–VI, Ln = La, Ce, Pr, Nd, Sm, and Eu) were hydrothermally synthesized and characterized. Single-crystal X-ray diffraction indicates that I–VI are isostructural and the lanthanide center is nine-coordinated with a distorted tetrakaidecahedral configuration. The as-synthesized Ln-MOFs are assembled into three-dimensional frameworks through the connections of dpc⁴⁻ ligands and hydrogen bonding interactions. Notably, Eu-MOF (VI) behaves as a multi-responsive luminescent sensor toward Fe³⁺, Cu²⁺, Cr₂O₇²⁻ and nitrobenzene with high sensitivity, selectivity, stability and anti-interference ability against the coexistence of other ions or molecules based on high luminescence quenching efficiency. Additionally, Eu-MOF (VI) shows excellent luminescence stability and retains its structural integrity within the pH range of 2–12 in an aqueous solution and its solid sample maintains high thermodynamic stability up to 320 °C. Furthermore, the possible luminescence sensing mechanisms have been discussed in detail, and are supported by PXRD analysis, UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS) or density functional theory (DFT).