Synthesis of Zr-based metal-organic framework/MWCNTs composite for adsorption of enrofloxacin from aqueous solution

Enrofloxacin, as one of the specialized fluoroquinolone antibiotics, has become a typical "emerging" pollutant in aqueous environment because of its great stability and resistance to degradation. Therefore, it is important to find an effective method to remove it from aqueous solution. In order to check the presence of synergies between UiO-66 and MWCNTs on removal of enrofloxacin from aqueous solution, a composite material, known as UiO-66/MWCNTs, was synthesized by using hydrothermal method. The physical and chemical properties of the synthesized composite were characterized by using methods such as XRD, N2 adsorption-desorption, FT-IR, SEM and XPS. The results revealed that UiO-66/MWCNTs has large specific surface area (837.56 m2/g) and high porosity, as well as rich functional groups (C = C, -OH, -COOH). Factors such as contact time, initial concen-tration, temperature, pH, and ionic strength were considered to test the adsorption performance of pristine MWCNTs, pristine UiO-66 and UiO-66/MWCNTs composite for enrofloxacin. The results showed that the UiO-66/MWCNTs composite has a higher adsorption capacity at basic condition and the maximum adsorption ca-pacities of enrofloxacin on composite was improved from 67.8 mg/g for MWCNTs and 92.8 mg/g for UiO-66 to 134.2 mg/g due to its higher adsorption active sites. The adsorption kinetics studies implied that the adsorption of enrofloxacin onto the studied sorbents involves in physio-chemical interactions and is an intra-particle diffusion controlling process. The isothermal experimental data were compatible with both Langmuir and Freundlich models, suggesting heterogeneous adsorption was the dominant during the course of adsorption. Additionally, the thermodynamic parameters indicated that the adsorption of enrofloxacin on UiO-66/MWCNTs was spontaneous and endothermic in nature. Finally, in combination with XPS analysis, the adsorption mech-anism of enrofloxacin on UiO-66/MWCNTs was clarified to be the synergetic effect of chemical adsorption, hydrogen bond and pi-pi interaction. This work provides a new strategy for the removal of drugs from aqueous environment.