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

A series of isostructural 3D lanthanide metal-organic frameworks (LnMOFs), with the formula n(H3O)[Ln(L)(H2O)](n)center dot nH(2)O (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 degrees 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 x 10(4) M-1), low detection limit (DL = 0.25 mu M) 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.