Unraveling the role of coordinated water in the capture of americium and toxic gases by an ultrastable uranyl phosphonate framework.

An ultrastable uranyl arylphosphonate framework as depleted uranium waste form with abundant coordinated water features marked entrapment of trivalent f-block elements (i.e., Eu3+, Am3+) from aqueous solutions as well as moderate uptake of toxic SO 2 and NH 3. The coordinated water can not only bind guest species together with phosphonate groups but also participate in the unprecedented Eu3+ → UO 2 2+ transmetalation. [Display omitted] • A highly robust uranyl phosphonate framework was fabricated. • UPF-205 features marked entrapment of Eu3+, Am3+ from aqueous solutions. • A hitherto unknown transmetalation between Eu3+ and UO 2 2+ was discovered. • The coordinated water binds guest species together with phosphonate groups. • The uptake of SO 2 significantly increased upon removing the coordinated water. The design and fabrication of uranium phosphonate frameworks (UPFs) pave a potential avenue to reduce the environmental risk of depleted uranium, transuranium waste, and toxic gases while adding to its waste to utility virtues. However, it remains unknown how the pervasive coordinated water of UPFs influences their performances in radionuclide and toxic gas separation. Toward this end, we prepared a new category of porous UPFs, namely UPF-205 with abundant coordinated water and resulting hydrogen bonding nanotraps. The coordinated water is synergistic in quantitatively removing trivalent f-elements (i.e., Am3+, Eu3+) from wide-ranging pH solutions together with proximal phosphonate groups at a low metal concentration. Most importantly, an unprecedented coordinated water-mediated Eu3+-UO 2 2+ transmetalation had been verified at a relatively high metal concentration. The high-density open uranyl sites and optimal pore size triggered by the dehydration of coordinated water also contribute to the enhanced adsorption of toxic SO 2 and NH 3. Our work shows great relevance for the rational design of ultrastable UPFs as both depleted uranium waste forms and efficient adsorbents for radiological/nuclear protection. [ABSTRACT FROM AUTHOR]