The post-synthetic modification of a Cd-MOF and its fluorescence sensing properties

In this work, a three-dimensional metal-organic framework, [Cd₃L₂(H₂O)]_n (Cd-MOF) was synthesized by using 2-(6-carboxypyridin-2-yl)terephthalic acid ligand (H₃L); and its post-synthetic modification composite, Eu@Cd-MOF was obtained by one-pot reaction of Eu³⁺ions with Cd-MOF. The FT-IR, PXRD, XPS, EDS, and fluorescence spectra were employed to verify the successful encapsulation of Eu³⁺ions into Cd-MOF. The luminescence measurements showed that Eu@Cd-MOF had a fluorescence quenching response with minocycline (MC), a widely used drug of broad-spectrum tetracycline antibiotics; and its limit of detection (LOD) for MC was 6.94 × 10^-8 M. It was worth pointing out that Eu@Cd-MOF had the characteristics of high selectivity, excellent selectivity, fast response time, and considerable recyclability in the identification of MC. The quenching mechanism of Eu@Cd-MOF by MC was investigated by the FT-IR, PXRD, UV-vis, and theoretical calculations of Materials Studio (MS). The above results indicated that the fluorescence quenching of Eu@Cd-MOF was caused by the acceptor photo-induced electron transfer process (a-PET) and the UV competition absorption. In addition, a hydrogel membrane based on Eu@Cd-MOF was also fabricated, which can be used to visually inspect MC with the naked eyes in practical applications.