Water-stable, sensitive sensors based on lanthanoid ions and a V-shaped linker 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) for the detection of the antibiotic sulfathiazole and potentially hazardous ions in polluted waters

Abstract

As long as metal-organic frames, MOFs, are known to possess properties such as good crystallinity, tunable pores, large surface area, they can be considered suitable for sensing of ions and organic molecules in waters. Powder samples with the composition ([Ln₂(FPB)₃]_∞ (Ln = Eu, Tb) and [Eu_0.2Tb_1.8(FPB)₃] are synthesized under solvothermal conditions to be tested as sensors; the fluorinated organic molecule 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) (H₂FPB) is used as a linker. The structure of the synthesized materials is elucidated by powder X-ray diffraction combined with structure having similar composition. Based on the adsorption/desorption isotherms the specific surface area is determined; values of 281, 257, and 286 m²/g for [Eu₂(FPB)₃], [Tb₂(FPB)₃] and [Eu_0.2Tb_1.8(FPB)₃] are attained, important for the Ln-MOFs as sensory materials. By diffuse-reflectance UV–Vis spectroscopy the light absorption of the samples is elucidated as well as by photoluminescence spectroscopy the action of the samples in solid state and in water suspension is followed. The behavior of the samples in media with different acidity is studied showing their stability in acidic and basic solutions in the pH interval 4–9. The luminescence of Ln-MOFs in the presence of different ions and antibiotics is studied in order to evaluate the sensitivity of the samples. Highest sensitivity to the presence of the antibiotic sulfathiazole (SFT) and to the ions Fe (III), Ag (I), Cr (VI), MnO₄^-, C₂O₄^2-, and H₂PO₄^- is detected. The response of the Ln-MOFs to the quenchers SFT, H₂PO₄^- and Cr(III) and Cr (VI) is evaluated based on the Stern-Volmer constants. Both the static and dynamic quenching mechanism are taken into consideration but the static mechanism is evidenced by the Stern Volmer linear dependence of the lifetime by the concentration of the analyte.