Highly pH-stable lanthanide MOFs: a tunable luminescence and ratiometric luminescent probe for sulfamethazine.

By selecting a bisphosphonic ligand HL (HL = 4-F-CHCHN(CHPOH)) and a coligand oxalate (HCO), three isostructural lanthanide metal-organic frameworks (Ln-MOFs) with a 2D layer structure, [Ln(HL)(CO)]·2HO (Ln = Eu (1), Gd (2), or Tb (3)), were hydrothermally prepared. By tuning the molar ratio of Eu, Gd, and Tb in the above reactions, six bimetallic or trimetallic doped Ln-MOFs (EuTb ( = 0.02 (4), 0.04 (5), and 0.06 (6)), GdEu (7), GdTb (8) and GdTbEu (9)) were obtained. The powder X-ray diffraction (PXRD) patterns of doped Ln-MOFs 4-9 show that they are isomorphous with 1-3. The bimetallic doped Ln-MOFs show a gradual variation of luminous colors between yellow-green, yellow, orange, pink, and light blue. Meanwhile, the trimetallic doped GdTbEu Ln-MOF (9) displays near white-light emission with a quantum yield of 11.39%. Interestingly, the luminous inks of 1-9 are invisible and color tunable, which makes it possible to promote their anti-counterfeiting applications. Additionally, 3 displays good thermal, water, and pH stabilities, which provides the feasibility for its sensing application. The luminescence sensing experiments show that 3 can serve as a highly selective, reusable, and ratiometric luminescent sensor of sulfamethazine (SMZ). Moreover, 3 shows an excellent SMZ detection performance in real samples, such as mariculture water and real urine. Owing to the visible variation of the response signal under a UV lamp, portable SMZ test paper was prepared.