Analyzing the adsorptive behavior of Amoxicillin on four Zr-MOFs nanoparticles: Functional groups dependence of adsorption performance and mechanisms

In this study, four functional Zr-MOFs (UiO-66-H, -NH2, -NO2, -Cl) were prepared, characterized (FESEM, XRD, BET, XPS, FT-IR) and compared to remove low-concentration Amoxicillin (AMX) from water. Then UiO-66-NH2 was selected for further experiments due to its highest adsorption capacity (2.3 +/- 0.4 mg g(-1)). The adsorption process followed pseudo-second order, Langmuir and Freundlich models. With pH increasing, deprotonation of functional groups in UiO-66-NH2 and AMX made adsorption interactions variable. The obvious spectra shift of FT-IR/XPS indicated that Lewis acid-base interaction was the main adsorption impetus; meanwhile hydrogen bonding interaction and pi-pi/n-pi (electron-donator-acceptor) EDA interaction should be included. For Lewis acidbase interaction, the strength was controlled by percentage of amine group in UiO-66-NH2, mainly interacting with phenolic hydroxyl group in AMX. Due to changes in charge distribution of functional groups, there existed six kinds of pi-pi/n-pi EDA interactions and thirteen types of hydrogen/pi-hydrogen bonding interactions. Additionally, electrostatic interaction and molecular attraction also contributed to the AMX adsorption. Conclusively, analysis of functional groups interactions could help to comprehend adsorption mechanisms more profoundly and exploit functional adsorbents more efficiently.