Self-assembled MOF microspheres with hierarchical porous structure for efficient uranium adsorption

[Display omitted] •Self-assembled zirconium (Zr)-MOF microspheres was synthesized by surfactant-assisted strategy for the first time.•Octahedron morphology and the inorganic–organic backbone of MOFs were preserved in microspheres.•MOF microspheres had hierarchical porous structure.•MOF microspheres showed excellent selective adsorption of uranium. Herein, the self-assembled zirconium (Zr)-MOF microspheres formed by the octahedral nano-building blocks (UiO-66 and its derivatives) to adsorb uranium (U) was presented for the first time. The self-assembled MOF microspheres achieved the growth across orders of magnitude from nanometers (∼50 nm) to micrometers (∼2.3 μm), and exhibited ordered hierarchical porous structure (from ∼0.6 nm to ∼340 nm). The self-assembled MOF microspheres combined the advantages of nanostructures with stability and microstructures with hierarchical porous structure for effective mass diffusion. The improved mass diffusion properties of amidoxime (AO)-appended MOF microspheres (P-UiO-66-AO) endowed them with superior adsorption performance and excellent selective adsorption of U compared with AO-appended MOF (UiO-66-AO) octahedron. The adsorption equilibrium was obtained within 1400 min, and the maximum adsorption capacity of U was 283.2 mg/g. The adsorption capacity of U in simulated seawater was determined to be 11.4 mg/g and the ratio of distribution coefficients of U and vanadium (V) (Kd/U/Kd/V) increased 1.75 times than that of UiO-66-AO octahedron, overcoming the challenge of competitive adsorption of U and V with MOF. Overall, the strategy to fabricate self-assembled MOF microspheres with nano-building blocks is expected to expand the diversity and range of potential applications of MOFs.