Dual-ligand two-dimensional terbium-organic frameworks nanosheets for ratiometric fluorescence detection of phosphate

Here, we reported a ratiometric fluorescence strategy for the detection of phosphate (Pi) in artificial wetland water. The strategy was based on dual-ligand two-dimensional terbium-organic frameworks nanosheets (2D Tb-NB MOFs). 2D Tb-NB MOFs were prepared through blending 5-boronoisophthalic acid (5-bop), 2-aminoterephthalic acid (NH2-BDC) and Tb3+ ions at room temperature in the presence of triethylamine (TEA). The dual-ligand strategy realized dual emission originated from ligand NH2-BDC and Tb3+ ions at 424 and 544 nm, respectively. Pi could compete with ligands to coordinate Tb3+ due to the strong binding ability between Pi and Tb3+, resulting in structural destruction of 2D Tb-NB MOFs, so static quenching and antenna effect between ligands and metal ions were interrupted, and emission at 424 nm was enhanced and emission at 544 nm was weakened. This novel probe had excellent linearity with Pi concentrations from 1 to 50 μmol/L; the detection limit was 0.16 μmol/L. This work revealed that mixed ligands improved sensing efficiency of MOFs by enhancing the sensitivity of the coordination between the analyte and MOFs.