High Sorption Capacity of U(VI) by COF-Based Material Doping Hydroxyapatite Microspheres: Kinetic, Equilibrium and Mechanism Investigation

Abstract

Most of heavy metal ions have toxicity, and some of them are radioactive, for example, the uranyl ion is one of the radioactive pollutants. Herein, the COF-based material doping hydroxyapatite microspheres (COF-HAP) has been synthesized and used for adsorbing the uranyl ions from aqueous solutions. We study and analyze the adsorption behavior by the sorption kinetic study, the sorption isotherms study, and the thermodynamics study. The adsorption can be made clear via three adsorption mechanisms, which cover the surface precipitate, surface complexation, and ion exchange. A series of characterizations about the COF-HAP make the structure of the adsorbent clearly, which include AFM, FTIR, XRD, SEM, and BET analysis techniques. The COF-HAP material enhances the adsorption capacity for U(VI) via doping the hydroxyapatite microspheres (HAP) into the COF-based material (COF-COOH). The maximum adsorption capacity of U(VI) on the COF-HAP is 510 mg g−1. The result provides an effective method about the removal of U(VI), so that it is possible that the inorganic–organic porous framework composite material will act as a candidate for the adsorption of heavy metal ions in future.