In situ synthesis of ZIF-8 on acid-activated kaolin composite for highly efficient U(VI) removal

Abstract

A novel composite, ZIF-8@AK, synthesized via in situ synthesis zeolitic imidazolate framework-8 (ZIF-8) on acid-activated kaolin (AK), was served as an adsorbent for U(VI) removal. The morphological characteristics and chemical composition of ZIF-8@AK were obtained through characterizations. Compared to KL, ZIF-8@AK possessed more functional groups and rougher surface with ordered pore structure, which supplied more active sites to adsorb U(VI), thus resulting in better U(VI) removal performances. Specially, the U(VI) separation capacity on ZIF-8@AK was up to 733.4 mg/g, much higher than that of KL (230.9 mg/g). Meanwhile, ZIF-8@AK still exhibited favorable recoverability with the separation rate of 89.7 % at the fifth cycle. Based on the conclusions of isotherm and kinetic models, the U(VI) separation process on ZIF-8@AK was mostly dependent on single-layer chemical reaction. Combining the results of SEM, FTIR, XRD and XPS for ZIF-8@AK before and after U(VI) separation, electrostatic interaction, coordination interaction and hydrogen bonds were the main interaction between ZIF-8@AK and uranyl. To sum up, this work supplied an appealing composite with high adsorption capacity and good recoverability, which was promising to be used for wastewater disposal.