Construction of Core–Shell MOFs@COF Hybrids as a Platform for the Removal of UO₂²⁺ and Eu³⁺ Ions from Solution

Abstract

The binary nanocomposites of metal/covalent-organic frameworks (NH₂-MIL-125(Ti)@TpPa-1) were constructed by solvothermal method, which was developed as a multifunctional platform with adsorption and photocatalysis for radionuclides removal. The batch experiments and physicochemical property (FT-IR, XRD, SEM, TEM, XPS, etc.) corroborated: (i) core-shell NH₂-MIL-125(Ti)@TpPa-1 had a more stable, multilayer pore structure and abundant active functional groups; (ii) NH₂-MIL-125(Ti)@TpPa-1 had fast a removal rate, as well as a high adsorption capacity of 536.73 mg (UO₂²⁺)/g and 593.97 mg (Eu³⁺)/g; (iii) the pseudo-second-order and Langmuir model provided a more reasonable description, indicating the immobilization process was endothermic, spontaneous chemisorption; (iv) the adsorption mechanism was chelation and electrostatic attraction, ascribed to the nitrogen/oxygen-containing functional groups. These results illustrated that NH₂-MIL-125(Ti)@TpPa-1 was a prospective adsorbent for the remediation polluted by radionuclides. In addition, the research provided the theoretical basis for further investigation on the UO₂²⁺(VI) photoreduction.