In-Situ Raman Spectroscopy Studies of Room-Temperature and Hydrothermal Reactions

Three uranium(VI)-bearing materials were synthesized hydrothermally using the organic ligand 4,4'-biphenyldicarboxylic acid: (UO2)(C14O4H8) (1); [(UO2)2(C14O4H8)2(OH)]·(NH4)(H2O) (2); (UO2)2(C14O4H8)(OH)2 (3). Compound 1 was formed after 1 day at 180 °C in an acidic environment (pH(i) = 4.03), and compounds 2 and 3 coformed after 3 days under basic conditions (pH(i) = 7.95). Coformation of all three compounds was observed at higher pH(i) (9.00). Ex situ Raman spectra of single crystals of 1-3 were collected and analyzed for signature peaks. In situ hydrothermal Raman data were also obtained and compared to the ex situ Raman spectra of the title compounds in an effort to acquire formation mechanism details. At pH(i) = 4.00, the formation of 1 was suggested by in situ Raman spectra. At an increased pH(i) (7.90), the in situ data implied the formation of compounds 1 and 3. The most basic conditions (pH(i) = 9.00) yielded a complex mixture of phases consistent with that of increased uranyl hydrolysis.

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“…The setup of the in situ Raman spectroscopy experiment has been described in detail earlier, yet Figure provides a schematic of the instrument …”

Section: Discussionmentioning

confidence: 99%