A stable LnMOF as a highly efficient and selective luminescent sensor for detecting malachite green in water and real samples

Abstract

A series of isostructural 3D lanthanide metal–organic frameworks (LnMOFs), with the formula n(H₃O)[Ln(L)(H₂O)]_n·nH₂O (Ln = Gd 1, Eu 2 and Tb 3, H₄L = 3,5,3′,5′-oxytetrabenzoic acid), have been successfully synthesized by solvothermal reactions. Single-crystal X-ray diffraction analysis reveals that 1–3 are constructed from wave-like Ln–carboxylate chains which are further connected by the ligands to form 3D channel-type frameworks. Further experiments suggest that 3 is thermally stable up to 322 °C and exhibits outstanding chemical stability in aqueous solutions with the pH ranging from 3 to 11. Significantly, 3 can be utilized for the first time to detect malachite green (a synthetic antibiotic to cure saprolegniasis) in aqueous media even in the presence of other interfering antibiotics, with a high sensitivity (K_sv = 8.33 × 10⁴ M⁻¹), low detection limit (DL = 0.25 μM) and good recyclability. On a more practical note, we found that the luminescence intensity of 3 showed almost no response to pH changes (pH 3–11), allowing steady sensing in real samples such as river water, simulated human serum and urine with satisfactory recoveries and RSD.