Microporous Cd-MOF as multifunctional material for rapid and visual luminescence sensing of Fe3+, MnO4− and TNP in water and efficient CO2 catalytic conversion

The excessive discharge of Fe3+, MnO4−, TNP and CO2 has resulted in serious environmental problems, which needs to be resolved urgently. Herein, a stable multifunctional Cd2+-organic framework, [Cd(H4L)]·2DMF·8H2O (Cd-MOF-1) was successfully constructed by using the ligand 4,4′,4″,4‴- (1,4-phenylenebis (1H-imidazole-2,4,5-triyl))tetrabenzoic acid (H6L) and Cd(NO3)2·2.5H2O under solvothermal conditions. Structural analysis revealed that Cd-MOF-1 possessed a 3D framework with rich Lewis acid sites (unsaturated Cd2+ sites), Brønsted acid sites (protonated imidazole moieties) and uncoordinated carboxylate oxygens in the hexagonal 1D channels. Moreover, Cd-MOF-1 exhibits good stability in acid-base aqueous solutions with pH = 4–12. Apart from the above structural features, Cd-MOF-1 also displays intense luminescence emission, which can be used to quickly and sensitively detect Fe3+, MnO4− and TNP in aqueous solutions with a high quenching constant and low detection limit even in the presence of other competition ions. Especially, the response time of the Cd-MOF-1 for Fe3+ ions was only 5 s, which is very short response time among the previous MOFs used for Fe3+ detection. Besides, we successfully constructed Cd-MOF-1/PEO mixed matrix films, which can achieve visualized quick detection of Fe3+, MnO4− and TNP in aqueous solutions under the UV lamp. In addition, activated Cd-MOF-1 (called Cd-MOF-1a) with all the guest molecules removed by heating delineates medium shows CO2 gas adsorption and efficient CO2 fixation with epoxide into cyclic carbonate under relatively mild and solvent-free conditions. On top of that, Cd-MOF-1 can be reused at least five cycles with excellent luminescence efficiency and catalytic activity. Furthermore, the possible luminescence sensing and catalytic mechanisms have also been discussed in detail. This work gives a new multifunctional platform for luminescence sensing and CO2 fixation.