No abstract

Certain anaerobic bacteria respire toxic selenium oxyanions and in doing so produce extracellular accumulations of elemental selenium [Se(0)]. We examined three physiologically and phylogenetically diverse species of selenate-and selenite-respiring bacteria, Sulfurospirillum barnesii, Bacillus selenitireducens, and Selenihalanaerobacter shriftii, for the occurrence of this phenomenon. When grown with selenium oxyanions as the electron acceptor, all of these organisms formed extracellular granules consisting of stable, uniform nanospheres (diameter, ϳ300 nm) of Se (0)

The limited thermal stability of alkylammonium cations intercalated into smectite minerals (e.g., montmorillonite, MMT) and the processing instability of some polymers [polyamide-6 (PA-6) and polystyrene (PS)] in the presence of nanodispersed MMT have motivated the development of improved organophillic treatments for layered silicates. Success in this regard should enable the preparation of polymer/layered silicate nanocomposites from thermoplastic polymers that require high melt-processing temperatures or long residence times under high shear and from thermoset resins with high cure temperatures. Our efforts to address some of these issues focus on the use of new thermally stable imidazolium-treated layered silicates for the preparation of nanocomposites. Several trialkylimidazolium salt derivatives were prepared with propyl, butyl, decyl, and hexadecyl alkyl chains attached to the imidazolium through one of the nitrogens. These imidazolium salts were used to prepare the corresponding treated layered silicates. We report here that the use of 1-alkyl-2,3-dimethylimidazolium salts to replace the sodium in natural MMT gives organophillic MMT with a 100 °C improvement in thermal stability (in N2) as compared to the alkylammonium-treated MMT. The use of 1-alkyl-2,3-dimethylimidazolium salt in fluorinated synthetic mica (FSM) also gives a 100 °C improvement in thermal stability. The use of 1,2-dimethyl-3-hexadecylimidazolium-treated MMT gives an exfoliated PA-6 nanocomposite and, depending on processing conditions, either a partially exfoliated or an intercalated polystyrene nanocomposite.

Fourier-transform infrared (FTIR) and time-resolved IR spectroscopies have been used to study vibrational band positions, vibrational energy relaxation (VER) rates, and reorientation times of anions in several ionic liquid (IL) solutions. The ILs primarily investigated are based on the 1-butyl-2,3-dimethylimidazolium ([BM(2)IM]) cation with thiocyanate (NCS-), dicyanamide (N(CN)2-), and tetrafluoroborate (BF4-) anions. Spectroscopic studies are carried out near 2000 cm-1 for the C[Triple Bond]N stretching bands of NCS- and N(CN)2- as the IL anion as well as for NCS-, N(CN)2-, and azide (N3-) anions dissolved in [BM2IM][BF4]. The VER studies of N(CN)2- are reported for the first time. VER of N3-, NCS-, and N(CN)2- is measured in normal solvents, such as N-methylformamide, to compare with the IL solutions. The spectral shifts and VER rates of the anions in IL solution are quite similar to those in polar aprotic, conventional organic solvents, i.e., dimethylsulfoxide, and significantly different than those in methanol, in which there is hydrogen bonding. Similar studies were also carried out for the anions in another IL, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), in which the C2 hydrogen is present. The results for the anions are similar to those in the [BM2IM] containing ILs, in which the C2 hydrogen is methyl substituted. This suggests that substituting this hydrogen has, at most, a minor effect on the degree of hydrogen bonding in the anion-IL solvation interaction based on the infrared spectra and dynamics.

Bromide-containing impurities were found to decrease the thermal stability of quaternary alkyl ammonium-modified layered silicates. Improved purification procedures completely removed bromide and led to a 20ºC to >100ºC increase in organic modified layered silicate thermal stability. Using mass spectrometry and thermal and electrochemical analysis, N,N-dimethyl-N,N-dioctadecyl quaternary ammonium-modified montmorillonite and fluorinated synthetic mica were found to degrade primarily through elimination and nucleophilic attack by these anions. The nature of residual bromides was identified and quantified, and the efficiency of removing these anions was found to be solvent dependent; sequential extraction, first ethanol then tetrahydrofuran, gave the best results. This exhaustive extraction method represents a viable alternative to the use of expensive, more thermally stable oniumion treatments for layered silicates.