The fabrication of 3D hierarchical flower-like δ-MnO2@COF nanocomposites for the efficient and ultra-fast removal of UO22+ ions from aqueous solution

Abstract

Herein, interpenetrating 3D flower-like δ-MnO₂@TpPa-1 composites were suitably constructed though the integration of δ-crystal manganese dioxide (δ-MnO₂) nano-flowers with a covalent organic framework (COF, TpPa-1) via adopting a simple ultrasonication process. The physicochemical properties of δ-MnO₂@TpPa-1 were characterized via SEM, TEM-EDX, XRD, FT-IR, pH_pzc, XPS, and N₂ adsorption–desorption studies. The kinetics of UO₂²⁺-ion adsorption onto δ-MnO₂ and δ-MnO₂@TpPa-1 confirmed the existence of a pseudo-second-order model. The results of isothermal experiments showed that the Langmuir model provided a better fit, illustrating a spontaneous, endothermic, and monolayer chemisorption process for UO₂²⁺ ions onto δ-MnO₂ and δ-MnO₂@TpPa-1. The maximum adsorption levels of UO₂²⁺ ions onto δ-MnO₂ and δ-MnO₂@TpPa-1 were 499.41 mg g⁻¹ and 1147.773 mg g⁻¹, respectively, at pH 6.5 and 298 K, owing to electrostatic attraction and inner-sphere surface complexation. Oxygen-containing groups played essential roles in the formation of U–O bonds and covalent Mn–O–U bonds, making δ-MnO₂@TpPa-1 an excellent adsorbent for radionuclide elimination from solution.