| AVS 66th International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Tuesday Sessions |
| Session AC+AS+LS-TuM |
| Session: | Chemistry and Physics of the Actinides and Rare Earths |
| Presenter: | Stefan Minasian, Lawrence Berkeley National Laboratory |
| Authors: | S.G. Minasian, Lawrence Berkeley National Laboratory S. Alayoglu, Lawrence Berkeley National Laboratory S. Aloni, Lawrence Berkeley National Laboratory J. Arnold, University of California at Berkeley E. Batista, Los Alamos National Laboratory A. Braun, Lawrence Berkeley National Laboratory C.H. Booth, Lawrence Berkeley National Laboratory A. Herve, Lawrence Berkeley National Laboratory Y. Liu, University of California at Berkeley L. Moreau, Lawrence Berkeley National Laboratory T. Lohrey, University of California at Berkeley J. Long, University of California at Berkeley M. Straub, University of California at Berkeley S. Robin, University of California at Berkeley D. Russo, University of California at Berkeley D.K. Shuh, Lawrence Berkeley National Laboratory J. Su, Los Alamos National Laboratory P. Yang, Los Alamos National Laboratory X. Zhang, Los Alamos National Laboratory |
| Correspondent: | Click to Email |
Decades of synthetic work has shown that desirable physical properties can be obtained by tailoring the size and composition of main-group and transition metal nanoparticles. The origin of these phenomena can be traced to a variety of factors that are intrinsic to nanoparticles, including but not limited to (1) quantization of the electronic states and (2) increasing contributions from nanoparticle surfaces. Despite this progress, very few methods provide the level of synthetic control needed to prepare lanthanide and actinide nanoparticles with well-defined sizes and compositions. Furthermore, many conventional methods of characterization are unable to determine the relative roles of volume and surface chemistry on physical behavior involving the 4f- and 5f-electrons.
We established syntheses for lanthanide and actinide nanoparticles by adapting a conceptual approach employed previously by Fischer and Suh to form d-block transition metal and main-group element nanoparticles in metal organic frameworks (MOFs). Implantation of lanthanide and actinide precursor molecules in covalent organic frameworks (COFs) was achieved by sublimation, followed by decomposition to form nanoparticles via exposure to reactive gases and/or elevated temperatures. A multi-pronged imaging and spectroscopic strategy was developed to fully characterize the complex multi-component materials. The characterization techniques are complementary in that they provide atomic to micron-scale probes, element and bulk-level selectivity, and measurements that are individual and statistically significant (Figure 1). Transmission electron microscopy (TEM) showed that the COF-5 templates limited UO2 nanoparticle growth to between 1-3 nm, which is similar to the COF-5 pore size (2.7 nm). In addition, small-angle X-ray scattering (SAXS) was used to determine the nanoparticle form factor (for size and polydispersity) in a globally-averaged manner. Scanning transmission X-ray microscopy (STXM) was used to probe micron-scale morphology and to evaluate composition with X-ray absorption spectroscopy at the B, C, and O K-edges. Finally, X-ray absorption fine structure (XAFS) spectroscopy was used to determine composition and structure because it does not require long-range crystallographic order, and because it is capable of probing the nanoparticles selectively despite the substantial background from the organic host. This presentation will also discuss our efforts to show how 4f and 5f-electron behavior changes with variations in size and composition at the nanometer level.