Flexible Ligands Constructed Metal–Organic Frameworks as Visual Test Paper for Fluorescent Detection

In this paper, four new metal–organic frameworks (MOFs) were synthesized by the solvothermal method based on two imidazolidyl flexible ligands, named, CUST-662–665, [Zn(pbbm)(HBTC)]·3H2O (CUST-662), [Cd2(pbbm)2(BTC)(NO3)·H2O]·2H2O (CUST-663), [Cd3(bbbm)3(BTC)2·4H2O]·3H2O (CUST-664), and [Zn2(bbbm)2(BTC)(HCOO)]·3H2O (CUST-665). All four MOFs with blue fluorescence show excellent performance in the detection of pollutants including Fe3+, Cr2O72–, trinitrophenol (TNP), and tetracycline antibiotics. Furthermore, the color of CUST-664 and CUST-665 changes from blue to yellow when detecting tetracycline (TC) and oxytetracycline (OTC), which can be further developed as simple and rapid field visual test paper as antibiotic detection devices. The detection limits of TNP, OTC, and TC can reach 0.36, 0.90, and 1.39 ppb, respectively, which are better than that of most of the reported fluorescence sensing materials. Moreover, CUST-662–665 display high selectivity, sensitivity, stability, and recycling efficiency. The competitive absorption between the crystals and pollutants was an important factor affecting fluorescence quenching. This work provides an experimental basis for subsequent fluorescence visualization field detection.