Highly sensitive fluorescent metal-organic framework as a selective sensor of Mn and Cr anions (MnO/CrO/CrO) in aqueous solutions.

A luminescent Zn-MOF named TMU-41, [Zn(BDC)(L)(DMF)]·1.5DMF, (L = pyridine 4-carboxylic acid and BDC = benzene-1,4-dicarboxylate), has been successfully assembled and well characterized by single-crystal X-ray crystallography, thermogravimetric analysis (TGA), X-ray diffraction (XRD) and N adsorption-desorption isotherms, which shows good stability especially in aqueous solutions. To fabricate open metal sites (OMS) of TMU-41(OMS), the coordinated DMF molecules were exchanged and removed by using acetonitrile as exchanging solvent and drying at 250 °C. The values of obtained surface areas after removing the coordinated DMF molecules are in the range of 740 m/g. This MOF indicates high potential ability in detection of anions due to its strong luminescence effect and stability in water. All these results suggest TMU-41(OMS) to be a highly selective and recyclable luminescent sensing material for the quantitative detection of Cr and Mn anions in aqueous solutions. TMU-41(OMS) has the highest sensing ability in comparison to the reported MOFs-based fluorescent and the detection limits towards MnO, CrO and CrO ions are about 5 ppb which is among the lowest reported detection limits for the LMOFs.