Understanding The Structural Chemistry of Actinide Phosphonates

As stockpiles of nuclear waste from both commercial spent nuclear fuel and nuclear weapons disarmament grow, a particular concern is the fate of the radioactive elements; namely uranium, neptunium, and plutonium. These elements pose grave danger if their long-term storage and possible release in the environment is not addressed in great detail. One method in addressing this problem is developing and designing advanced waste forms that sequester these elements that are not degraded by either radiation or environmental effects. Actinide phosphates have proven to be promising candidates in this regard. Traditional routes to ceramic waste forms require the use of high temperatures (>1000Ìâå¼C) and long reaction times. My doctoral research has focused on the development of low-temperature hydrothermal crystal growth methods for synthesizing actinide phosphonates that can be thermally or radiolytically decomposed to phosphates at relatively low temperatures. In addition, the structural chemistry of actinide phosphonates is of great interest, and developing their structure-property correlations is one of the main goals in my research matriculation. Using structural data, we are illuminating the similarities and differences in bonding between uranium and transuranium phosphonates.A compilation of published results from my doctoral research will seek to provide a better insight and understanding of phosphonates with actinide elements; exploring the preparation, structural characterization, and physical properties in this class. To accomplish this, the use of in situ hydrothermal redox chemistry was used in the synthesis of these novel compounds. Standard spectroscopic techniques such as vibrational spectroscopy, Raman, UV-vis-NIR spectroscopy, and second-harmonic generation(SHG) measurements were also used to determine structure-property relationships, but single crystal X-ray diffraction was the primary means of characterization in elucidating the structures of these new compounds. Examples of the structures of thorium, uranium, neptunium, and plutonium diphosphonates, and well-characterized heterobimetallic mixed-actinide phosphonates are provided. These compounds demonstrate the versatility and flexibility of a polydentate phosphonate with the actinides.