Uranyl peroxide cage clusters form upon addition of peroxide to an aqueous solution of uranyl nitrate and adjusting the pH with base. These clusters are unique in actinide chemistry in that they form an extensive family of nanoscale capsules that have several potential applications. Two of these, designated U60 and U24P, are the subject of the current study. U60 consists of sixty uranyl peroxide hydroxide polyhedra that are linked into a fullerene topology that is identical to C60. U24P contains four-membered rings of uranyl ions bridged through peroxide that are linked into the capsule through pyrophosphate units. We are interested in methods to separate clusters in aqueous solution on the basis of their size or mass. In the current study, filtration of cluster species was used to separate U60 cage clusters from U24P cage clusters by taking advantage of the difference in their sizes. The U60 and U24P clusters were synthesized separately and mixed together in a feed solution. Electrospray ionization mass spectrometry (ESI-MS) and small-angle X-ray scattering (SAXS) confirmed the presence of both of the clusters in the original feed solution before filtration. A Millipore Amicon stirred cell along with flat sheet ultrafiltration membranes with reported molecular weight cutoffs of 8, 10, 12-14, and 20 kDa (based on polyethylene glycol and dextran standards) were used to execute filtration experiments. Using ESI-MS and SAXS to analyze the solution that permeates through the membrane, preliminary filtration experiments indicate that microporous membranes with a molecular weight cutoff of 12-14 kDa are capable of achieving a size-selective separation of U60 and U24P. This method of separation can also be used in studying time-resolved growth data of co-growth nanoclusters such as U60 and U24.

Separating uranyl nanoclusters using ultrafiltration membranes

249th National Meeting (2015)

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