High efficient removal of U(VI) by covalent organic frameworks fabricated by mechanochemical method: Adsorption process, mechanism and surface complexation modeling

Herein, covalent organic frameworks (i.e., TpBD) were fabricated by mechanical delamination of 1, 3, 5-triformylphloroglucinol (Tp) and benzidine (BD) using NaHCO3 as foaming agent. The batch characterizations revealed that flower-like TpBD nanosheets exhibited the large porosity, high BET specific area (139 m2/g), small pore size (∼ 14 Å), remarkable stability and keto form. The adsorption process of U(VI) removal by TpBD displayed the fast sorption rate (equilibrium within 0.5 h), high adsorption capacity (167 mg/g) and good re-usability (no significant difference after five cycles). According to analysis of X-ray photoelectron spectroscopy (XPS) and surface complexation modeling, the removal mechanism of U(VI) by TpBD was chemisorption and inner-sphere surface complexation. These findings are of great importance for the application of covalent organic frameworks fabricated with rapid and easy-to-operate mechanochemical method in actual environmental cleanup.