Adsorption Behaviors of Organic Micropollutants on Zirconium Metal–Organic Framework UiO-66: Analysis of Surface Interactions

Herein, we studied the adsorption behaviors of organic micropollutants, such as anticonvulsant carbamazepine (CBZ) and antibiotic tetracycline hydrochloride (TC), on zirconium metal–organic framework UiO-66 in water. The maximum adsorption capacities of CBZ and TC on the UiO-66 were 37.2 and 23.1 mg·g^–1 at 25 °C, respectively. The adsorption isotherms and kinetics of CBZ and TC were well described by using the Langmuir model and pseudo-second-order model, respectively, and the adsorptions on UiO-66 are endothermic reactions. The adsorption capacities of CBZ and TC on UiO-66 were decreased with the increase of solution pH. The presence of humic acid could improve the adsorption of CBZ and TC on UiO-66, but K⁺ ion inhibited their adsorption obviously. In addition, Ca²⁺ and Al³⁺ ions also suppressed the adsorption of TC on UiO-66. The competitive adsorption suggested that the adsorption sites for CBZ on UiO-66 were different from those for TC. The surface interactions between UiO-66 and the two micropollutants were demonstrated by powder X-ray diffraction, Fourier transform infrared (FT-IR) spectra, scanning electron microscopy, nitrogen adsorption/desorption isotherms, and X-ray photoelectron (XPS) spectra. The characterizations showed that the adsorption of CBZ on UiO-66 is mainly a physisorption, and the hydrophobic effect played a crucial role during the adsorption of CBZ; meanwhile weak π–π electron donor–acceptor interaction and electrostatic attraction also existed. However, the adsorption of TC on UiO-66 is mainly a chemisorption; in addition to the strong electrostatic attraction and π–π electron donor–acceptor interaction forces, the nitrogenous groups of TC played an important role, which can replace the carboxylic groups coordinated with Zr–O clusters. The obtained results will aid us to comprehend the surface interaction between organic micropollutants and UiO-66 and expand the application of UiO-66 as sorbent for removal of pollutants from water.