Decontamination of metal surfaces contaminated with low levels of radionuclides is a major concern at Department of Energy facilities. The development of an environmentally friendly and cost-effective decontamination process requires an understanding of their association with the corroding surfaces. We investigated the association of uranium with the amorphous and crystalline forms of iron oxides commonly formed on corroding steel surfaces. Uranium was incorporated with the oxide by addition during the formation of ferrihydrite, goethite, green rust II, lepidocrocite, maghemite, and magnetite. X-ray diffraction confirmed the mineralogical form of the oxide. EXAFS analysis at the U L III edge showed that uranium was present in hexavalent form as a uranyl oxyhydroxide species with goethite, maghemite, and magnetite and as a bidentate innersphere complex with ferrihydrite and lepidocrocite. Iron was present in the ferric form with ferrihydrite, goethite, lepidocrocite, and maghemite; whereas with magnetite and green rust II, both ferrous and ferric forms were present with characteristic ferrous:total iron ratios of 0.65 and 0.73, respectively. In the presence of the uranyl ion, green rust II was converted to magnetite with concomitant reduction of uranium to its tetravalent form. The rate and extent of uranium dissolution in dilute HCl depended on its association with the oxide: uranium present as oxyhydroxide species underwent rapid dissolution followed by a slow dissolution of iron; whereas uranium present as an inner-sphere complex with iron resulted in concomitant dissolution of the uranium and iron.

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Featured Application: Detailed chemical and structural changes to polylactid acid (PLA) from source material through 3D printing needs to be quantified in order to use PLA 3D printed structures for specific applications. This work was specifically motivated for specific applications for in situ synthesis of silver nanoparticles on printed PLA surfaces used in antimicrobial applications and the development and characterization of PLA constructs for tissue engineering.Abstract: Polylactic acid (PLA) is an organic polymer commonly used in fused deposition (FDM) printing and biomedical scaffolding that is biocompatible and immunologically inert. However, variations in source material quality and chemistry make it necessary to characterize the filament and determine potential changes in chemistry occurring as a result of the FDM process. We used several spectroscopic techniques, including laser confocal microscopy, Fourier transform infrared (FTIR) spectroscopy and photoacousitc FTIR spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) in order to characterize both the bulk and surface chemistry of the source material and printed samples. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to characterize morphology, cold crystallinity, and the glass transition and melting temperatures following printing. Analysis revealed calcium carbonate-based additives which were reacted with organic ligands and potentially trace metal impurities, both before and following printing. These additives became concentrated in voids in the printed structure. This finding is important for biomedical applications as carbonate will impact subsequent cell growth on printed tissue scaffolds. Results of chemical analysis also provided evidence of the hygroscopic nature of the source material and oxidation of the printed surface, and SEM imaging revealed micro-and submicron-scale roughness that will also impact potential applications.

Speciation of uranium in cultures of Clostridium sp. by X-ray absorption near-edge spectroscopy (XANES) at the National Synchrotron Light Source and by X-ray photoelectron spectroscopy (XPS) showed that U(VI) was reduced toU(IV). In addition toU(IV), a lower oxidation state of uranium, most probably U(III), was detected by XANES in the bacterial cultures. Reduction of uranium occurred only in the presence of growing or resting cells. Organic acid metabolites, the extracellular components of the culture medium, and heat-killed cells failed to reduce uranium under anaerobic conditions. The addition of uranyl acetate or uranyl nitrate (>210 µ U) to the culture medium retarded the growth of the bacteria as evidenced by an increase in the lag period before resumption of growth, by decreases in turbidity, and in the total production of gas and organic acid metabolites. These results show that uranium in wastes can be stabilized by the action of anaerobic bacteria.

Diiodobutadiyne forms cocrystals with bis(pyridyl)oxalamides in which the diyne alignment is near the ideal parameters for topochemical polymerization to the ordered conjugated polymer, poly(diiododiacetylene) (PIDA). Nonetheless, previous efforts to induce polymerization in these samples via heat or irradiation were unsuccessful. We report here the successful ordered polymerization of diiodobutadiyne in these cocrystals, by subjecting them to high external pressure (0.3-10 GPa). At the lower end of the pressure range, the samples contain primarily monomer, as demonstrated by X-ray diffraction studies, but some polymerization does occur, leading to a pronounced color change from colorless to blue and to the development of intense Raman peaks at 962, 1394, and 2055 cm-1, corresponding to the poly(diacetylene). At higher pressures, the samples turn black and contain primarily polymer, as determined by solid-state NMR and Raman spectroscopy. Both density functional theory calculations (B3LYP/LanL2DZ) and comparisons to authentic samples of PIDA have confirmed the data analysis.