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 π-π 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.