Dual Lanthanide (Eu–Tb) Doped 2D MOFs with Tunable Multicolor Emission for Fluorescence Sensing

Due to their unique luminescence properties, long lifetimes, and large Stokes shifts, lanthanide metal ions (Ln3+) serve as an important metal source for the construction of fluorescent MOFs. In this study, two isostructural two-dimensional lanthanide metal–organic frameworks, CUST-528 and CUST-529, were reported. Under solvothermal conditions, these frameworks were successfully synthesized using the ligands 2,4,6-tri(2-pyridinyl)-1,3,5-triazine (TPTZ) and 2-bromoterephthalic acid (2-BrTA), along with Eu(NO3)3·6H2O and Tb(NO3)3·6H2O. The PXRD patterns indicated that CUST-528 and CUST-529 maintained their crystalline structure and exhibited good stability in an aqueous environment for 10 days. In the fluorescence sensing experiments, the two crystals exhibited good detection capability, selectivity, and sensitivity toward NOR, Fe3+, Cr2O72–, and TNP, respectively. By adjusting the mass ratio of Eu3+ to Tb3+, a series of dual-lanthanide emissive EuxTb1–x-MOF materials were successfully developed. Eu0.6Tb0.4-MOF was further applied to ratiometric and hydrogel-based visual sensing of norfloxacin. During the detection process, a systematic investigation of the possible mechanisms of fluorescence quenching was conducted.