U(VI) immobilization properties on porous dual metallic M/Co(II) zeolitic imidazolate framework (ZIF-67) (M = Fe(III), Ni(II), Cu(II)) nanoparticles

Porous dual metallic M/Co(II) zeolitic imidazolate framework (ZIF-67) (M = Fe(III), Ni(II), Cu(II)) nanoparticles have been successfully fabricated through one-step synthesis process at room temperature. And the obtained samples were characterized through XRD, FT-IR, TEM, and BET to understand its high crystal purity, functional groups, and porous structure. The M/Co(II)-ZIF-67 nanoparticles possessed a large number of mesopores as well as high surface area. Moreover, by changing the type of doped metal ions in the ZIF-67, its capacity for U(VI) immobilization also suffers a change with its adsorption capacity hierarchy of Fe/Co-ZIF-67 (552.19 mg∙g−1) > ZIF-67 (392.13 mg·g−1) > Ni/Co-ZIF-67 (373.74 mg·g−1) > Co/Cu-ZIF-67 (360.82 mg·g−1) at pH ∼ 5.5, and 298 K. And the changes in U(VI) immobilization capacity can be ascribed to that the doped metal ions could break the distribution of Co(II) in the crystal structure of ZIF-67 and further affects its physical and chemical properties. Moreover, the possible mechanism for U(VI) immobilization could be concluded as follows: U(VI) ions firstly diffused and interacted with M/Co(II)-ZIF-67 materials adequately due to high surface area and the pore structure. Subsequently, the U(VI) combined with the active sites of functional groups such as –OH, –NH and CN groups. This work demonstrated the high capacity for U(VI) immobilization applications by dual metallic M/Co(II) zeolitic imidazolate framework and provided a glimpse into tailoring and designing the zeolite structure to enhance the physicochemical properties.