Development of a Fibrous Adsorbent Prepared Via Green Vapor-Phase Grafting Polymerization for Uranium Extraction.

Owing to many problems of the detriment by large amount of organic reagents, high cost and difficulty of industrialization, development of high-efficiency economical technologies for uranium extraction is an irresistible trend to support steady supply of nuclear energy. Herein, a novel fibrous adsorbent, named as AO-HPE fibers, was prepared by introduction of amidoxime groups using the green vapor-phase grafting polymerization (VPGP) technology of monomer acrylonitrile (AN). Gaseous AN was grafted onto the ultra high molecular weight polyethylene (UHMWPE) fibers at 80 °C in the enclosed evaporation and condensation reflux system. The innovative technology not only endowed synthetic process high monomer utilization ratio but also excellent environmental friendliness. The AO-HPE fibers exhibited an appreciable calculated maximum adsorption capacity (Q m) of 1144.94 mg·g-1 in uranium solution and an adsorption capacity of 14.11 mg·g-1 in simulated seawater. Meanwhile, the higher uranium selectivity than main competing ion vanadium (adsorption mass ratio was almost 5) was achieved. The adsorption process accorded closely with chemisorption mechanism. This work provided a novel idea for the synthetic method of adsorbents for uranium extraction, and inspired the sustainable technologies for grafting polymerization of monomer AN.

UiO-66-NH-(AO) MOFs with a New Ligand BDC-NH-(CN) for Efficient Extraction of Uranium from Seawater.

Metal-organic frameworks (MOFs) with a high surface area and excellent stability are potential candidates for uranium (U) adsorption. Amidoxime (AO) is the most widely used functional group to extract U, which is usually introduced into MOFs by two-step post-synthetic methods (PSMs). Herein, MOF UiO-66-NH-(AO) was obtained by a one-step PSM with amidoximation from UiO-66-NH-(CN), which was synthesized by a new organic ligand of 2-cyano-terephthalic acid and whose morphology was octahedron and could be well controlled with the new ligand. The one-step PSM can greatly maintain the octahedron of the MOFs. What is more, UiO-66-NH-(AO) showed good adsorption performance for U, the adsorption equilibrium was obtained within 1500 min, and the adsorption capacity of U was calculated to be 134.1 mg/g according to the Langmuir model. It also had excellent selectivity for U in the presence of high concentrations of vanadium (V), ferrum (Fe), magnesium (Mg), calcium (Ca), and zirconium (Zr). The adsorption capacity of U in natural seawater was determined to be 5.2 mg/g within 8 days. The recyclability of UiO-66-NH-(AO) in simulated seawater was demonstrated for at least four adsorption/desorption cycles. The binding mechanism was investigated by the extended X-ray absorption fine structure spectroscopy, revealing that U binding occurs in a fashion η2 motif. This study provides a reliable idea for the modification of MOFs and the potential for MOF-based materials to extract U from seawater.