Tetracycline removal from aqueous solution using zirconium-based metal-organic frameworks (Zr-MOFs) with different pore size and topology: Adsorption isotherm, kinetic and mechanism studies

The adsorptive removal of tetracycline (TC) was studied with three types of zirconium-based metal-organic frameworks (Zr-MOFs), UiO-66, NU-1000 and MOF-525. The adsorption kinetics best fitted with the pseudo-second-order kinetic model and the adsorption equilibrium was rapidly reached within 40 min on UiO-66 and NU-1000, and 120 min on MOF-525. The adsorption isotherms best fitted with Sips model, and the maximum Sips adsorption capacities of TC on UiO-66, NU-1000 and MOF-525 were 145 mg.g(-1), 356 mg.g(-1) and 807 mg.g(-1) respectively, which were much higher than common adsorbents. The X-ray photoelectron spectra measurements and the influence of pH suggested that the pi-pi interaction played a crucial role during the adsorption. Pore characteristics and topology of MOFs showed great effect on adsorption performance. The cages whose size match well with TC helped MOF-525 to get highest adsorption amount per surface area among MOFs we studied. The proper topology of NU-1000 contributed to its high adsorption rate. River water was also used to confirm the excellent adsorptive performance of these three Zr-MOFs in practical application. These results might aid us to comprehend the adsorption of TC on Zr-MOFs and expand the application of Zr-MOFs in water treatment for removal of emerging contaminants. (C) 2021 Published by Elsevier Inc.

Automated summary

Three zirconium-based metal-organic frameworks, UiO-66, NU-1000, and MOF-525, demonstrated excellent adsorption performance for tetracycline removal. The adsorption kinetics were best described by the pseudo-second-order model, with equilibrium rapidly reached within 40 minutes on UiO-66 and NU-1000, and within 120 minutes on MOF-525. The Sips model provided the best fit for the adsorption isotherms, with high maximum Sips adsorption capacities reported for all three MOFs. The pi-pi interaction was found to play a crucial role in the adsorption process.