33 research outputs found
Anionic effects observed in complexes of trivalent lanthanides with partitioning relevant N-donor ligands
Synthesis and characterization of thorium, uranium and cerium oxide nanoparticles
We describe the synthesis of cerium, thorium and uranium oxide nanoparticles embedded in a mesoporous matrix as template in a kind of nanocasting technique. The solid matrix is used as a template to obtain and stabilize the actinide oxide nanoparticles. We apply high resolution transmission electron microscopy (HR-TEM) to show evidence of metal oxide incorporation into the matrix pores and analyze their structure. Measured interplanar distances and calculated lattice parameters for synthesized nanosized CeO2âx and ThO2 samples differ from their bulk crystalline counterparts. We obtain with our synthesis CeO2âx particles containing both Ce4+ and larger sized Ce3+. The lattice parameter for these ceria nanoparticles is found to be larger than the bulk value due to the presence of Ce3+ with its larger ionic radius. The presence of Ce3+ was established by means of high resolution X-ray emission spectroscopy (HRXES), applied to the investigation of nanoparticles for the first time. The ThO2 nanoparticles exhibit a decrease in interplanar distances, as one might generally expected for these nanoclusters. However, the lattice distance decrease for our particles is remarkable, up to 5%, indicating that contact with the surrounding silica matrix may exert a bond distance shortening effect such as through significant external pressure on the particle surface
Sulfur incorporation in high level nuclear waste glass: a S K-edge XAFS investigation
We perform X-ray absorption fine structure (XAFS) spectroscopy measurements at the sulfur K-edge to elucidate the electronic and geometric bonding of sulfur atoms in borosilicate glass used for the vitrification of high level radioactive liquid waste. The sulfur is incorporated as sulfate, most probably as sodium sulfate, which can be deduced from the X-ray absorption near edge structure (XANES) by fingerprint comparison with reference compounds. This finding is backed up by Raman spectroscopy investigation. In the extended XAFS data, no second shell beyond the first oxygen layer is visible. We argue that this is due to the sulfate being present as small clusters located into voids of the borosilicate network. Hence, destructive interference of the variable surrounding prohibits the presence of higher shell signals. The knowledge of the sulfur bonding characteristics is essential for further optimization of the glass composition and to balance the requirements of the process and glass quality parameters, viscosity and electrical resistivity on one side, waste loading and sulfur uptake on the other side
Comparative NMR study of partitioning-relevant complexes with trivalent actinides and lanthanides to elucidate the origin of their selectivity
EXAFS structural analysis of aqueous uranium(VI) complexes with lignin degradation products
Soft X-ray spectro-microscopy investigation of the formation and ageing of Eu(III)-induced humic acid aggregates
Aggregation of Aldrich humic acid at pH 4.3 and after loading with Eu(III)-cations at pH 5.3 is
investigated by scanning transmission X-ray microscopy (STXM). 1s-NEXAFS spectra extracted from STXM
image stacks for the low pH aggregates show no significant variation, whereas Eu(III)-humate formation is observed
to be accompanied by segregation into zones with different optical densities. These zones exhibit distinctly different
NEXAFS features, indicative of the presence of a separation of organic species or components. Increasing humate
aggregate densification over a period of several months is observed. The spectrum of the unloaded HA cannot be
reproduced by a superposition of spectra extracted from the segregated humate zones; there is a distinct metal
bonding effect on the molecular states of the functional groups involved in complexation