Crystal engineering of novel MOF@iCOF composite as a multifunction platform for targeted monitoring and capturing of norfloxacin

The construction of novel multifunctional nanocomposites is of interest because of their excellent proven detection and capture performance. Herein, a new type of porous material, UiO-66-NH2@TpTGCl, is designed by combining a Zr-based metal organic framework, UiO-66-NH2, with a guanidine-based ionic covalent organic framework (iCOF), TpTGCl. The UiO-66-NH2@TpTGCl retains the high crystallinity and hierarchical pore structure of the MOF and iCOF, and has a surface rich in guanidine groups, and hence it has excellent hydrophilicity and is rich in positively charged sites; thus, the potential capacity of UiO-66-NH2@TpTGCl for the capture of antibiotics with polar functional groups, such as norfloxacin, is excellent. Tb3+ ions are then assembled onto the UiO-66-NH2@TpTGCl skeleton. With the addition of norfloxacin to the composite, strong coordination between the carboxyl group of norfloxacin and the Tb3+ ions in UiO-66-NH2@TpTGCl@Tb occurred, and the characteristic fluorescence emission of Tb3+ (5D4 -> 7F5) is enhanced by antenna and spatial confinement effect. Consequently, ratiometric fluorescence detection and capture of norfloxacin are realized using UiO-66-NH2@TpTGCl@Tb. The linear detection range is 0.01-1 mu M and the detection limit is 4 nM. Most importantly, UiO-66-NH2@TpTGCl@Tb exhibits high capture capacity (251 mg g-1) and favorable capture efficiency (80.5%). Meanwhile, the mechanism is detailed explored through XPS spectrum and DFT calculation. We believe that this work will trigger the study of new iCOF-functionalized MOF composites and that it presents a promising strategy for simultaneous ratiometric luminescence monitoring and capturing of antibiotics from water.

Automated summary

A novel porous material UiO-66-NH2@TpTGCl was designed and successfully applied for ratiometric fluorescence detection and capture of the antibiotic norfloxacin. The material displayed excellent hydrophilicity, rich in positively charged sites, high capture capacity, and favorable capture efficiency.