Vibrational spectroscopic studies of N719 dye-adsorbed TiO(2) films have been carried out by using SERRS, ATR-FTIR, and confocal Raman imaging. The high wavenumber region (3000-4000 cm(-1)) of dye adsorbed TiO(2) is analyzed via Raman and IR spectroscopy to investigate the role of surface hydroxyl groups in the anchoring mode. As a complementary technique, confocal Raman imaging is employed to study the distribution features of key dye groups (COO-, bipyridine, and C=O) on the anatase surface. Sensitized TiO(2) films made from two different nanocrystalline anatase powders are investigated: a commercial one (Dyesol) and our synthetic variety produced through aqueous synthesis. It is proposed the binding of the N719 dye to TiO(2) to occur through two neighboring carboxylic acid/carboxylate groups via a combination of bidentate-bridging and H-bonding involving a donating group from the N719 (and/or Ti-OH) units and acceptor from the Ti-OH (and/or N719) groups. The Raman imaging distribution of COO(-)(sym) on TiO(2) was used to show the covalent bonding, while the distribution of C=O mode was applied to observe the electrostatically bonded groups.

In this study, the electronic properties of N719 adsorbed onto anatase were comparably investigated by using X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) techniques. Sensitized TiO2 films made from two different nanocrystalline anatase powders were investigated: a commercial one (Solaronix) and our synthetic variety produced through aqueous synthesis. This was done to investigate how our aqueous-produced nanocrystalline anatase substrates compared with commercial products and to observe whether both nanocrystalline anatase anodes behaved in a similar manner in terms of their bonding and electronic interactions. Surface coordination changes to Ti−O groups previously reported via Ti K-edge extended X-ray absorption fine structure (EXAFS) data [using transmission or fluorescence yield (FY)] between the pure TiO2 and the adsorbed state were not observed in our measurements via the Ti L or K X-ray absorption near-edge structure (XANES) (nor EXAFS) data for both substrates via a surface-sensitive detection technique (total electron yield, TEY). This is likely due to the probing depth of TEY mode (5−10 nm), in which the coordination changes that occur to the surface groups, which should in turn affect the XANES spectrum, are not observed at Ti K- or L-edge XANES spectrum. The C and N K-edge XANES spectra of the N719 adsorbed onto two TiO2 films were for the first time evaluated in this work. From the C K-edge XANES data, the spectral changes revealed that additional electronic states occur between dye molecules and TiO2 surface. The C K-edge XANES spectra allowed us to propose that electronic interactions do not only occur through the covalent bonding of the anchoring groups but also through the aromatic electron density of the bipyridine groups and the d states found in TiO2. This was further confirmed via XPS analysis by monitoring the N bipyridine groups before and after sensitization. XPS used in combination with XAS (in TEY mode) provided complementary information owing to its higher surface sensitivity. The Ti 2p and O 1s XPS spectra showed that adsorption of the dye on TiO2 leads to a change of the surface dipole and/or a change in the Fermi level position in the band gap, which shifts all the core levels of TiO2. These are not equal for both TiO2 substrates in spite of them being nanocrystallnine anatase. This effect was found to be greater for the N719−aqueous TiO2 system than the respective Solaronix one. For the N 1s and S 2p XPS, the shift toward higher energy indicated that there exists an additional H-bonding interaction of the NCS ligand of the dye molecule with the TiO2 surface groups (OH/H2O).

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Three crystalline ferric arsenate phases: (1) scorodite; FeAsO 4 ·2H 2 O, (2) ferric arsenate sub-hydrate (FAsH; FeAsO 4 ·0.75H 2 O) and (3) basic ferric arsenate sulfate (BFAS; Fe[(AsO 4 ) 1−x (SO 4 ) x (OH) x ]·wH 2 O) synthesized by hydrothermal precipitation (175-225 • C) from Fe(III)-AsO 4 3− -SO 4 2− solutions have been investigated via Raman and infrared spectroscopies. The spectroscopic nature of these high-temperature Fe(III)-AsO 43− -SO 4 2− phases has not been extensively studied despite their importance to the hydrometallurgical industrial processing of precious metal (Au and Cu) arsenic sulfidic ores. It was found that scorodite, FAsH and BFAS all gave rise to very distinct arsenate, sulfate and hydroxyl vibrations. In scorodite and FAsH, the distribution of the internal arsenate modes was found to be distinct, with the factor effect being more predominant in the crystal system. For the crystallographically unknown BFAS phase, vibrational spectroscopy was used to monitor the arsenate ↔ sulfate solid solution behavior that occurs in this phase where the molecular symmetry of arsenate and sulfate in the crystal structure is reduced from an ideal T d to a distorted T d or C 2 /C 2v symmetry. With the new collected vibrational data of the pure phases, the use of attenuated total reflectance infrared (ATR-IR) spectroscopy was finally extended to investigate the nature of the arsenate in an industrial residue generated by pressure oxidation of a gold ore, where it was found that the arsenate was present in the form of BFAS.

The mineralogy and evolution of Al and Mg in U mill tailings are poorly understood. Elemental analyses (ICP-MS) of both solid and aqueous phases show that precipitation of large masses of secondary Al and Mg mineral phases occurs throughout the raffinate neutralization process (pH 1-11) at the Key Lake U mill, Saskatchewan, Canada. Data from a suite of analytical methods (ICP-MS, EMPA, laboratory- and synchrotron-based XRD, ATR-IR, Raman, TEM, EDX, ED) and equilibrium thermodynamic modeling showed that nanoparticle-sized, spongy, porous, Mg-Al hydrotalcite is the dominant mineralogical control on Al and Mg in the neutralized raffinate (pH ≥ 6.7). The presence of this secondary Mg-Al hydrotalcite in mineral samples of both fresh and 15-year-old tailings indicates that the Mg-Al hydrotalcite is geochemically stable, even after >16 years in the oxic tailings body. Data shows an association between the Mg-Al hydrotalcite and both As and Ni and point to this Mg-Al hydrotalcite exerting a mineralogical control on the solubility of these contaminants.

The abiotic reduction of X-ferrihydrite (X-FH, where X ¼ 0, As, Mo, or Ni at various Fe/X molar ratios) was investigated by reacting Fe(II) (aq) at solution concentrations of 0.5 mM or 10 mM and at target pH values of 8 or 10 (using lime water as a base) for 7 days. Under all reaction conditions tested, the measured pH was always lower than the target; this difference was greatest for As-FH (at up to 5 pH units). The control FH sample behaved as expected and transformed to lepidocrocite (LP) and goethite (GT) phases. For As-FH, the sample containing less As (Fe/As ¼ 32.9) transformed to LP-GT phases but phase transformation in the sample with more As (Fe/As ¼ 4.47) was inhibited. Solution concentrations of As were below the detection limit for the Fe/As 32.9 sample but As release was evident for the Fe/As 4.47 sample. For Mo-FH, phase transformation to LP-GT phases was observed at lower target pH (8) conditions under both reacting Fe(II) (aq) concentrations. At the higher target pH (10) and using 0.5 mM Fe(II) (aq) , phase transformation inhibition was observed for Mo-FH varieties that contained both high (Fe/Mo 12.5) and low (Fe/Mo 31.5) concentrations of Mo. This is the first time an element forming an outer-sphere complex on FH (e.g., Mo) has been shown to retard phase transformation; such phenomena are usually observed for metalloids that form inner-sphere complexes with FH (e.g., As). Under all conditions, Mo was released into solution (up to 340 ppm) and under some conditions was then readsorbed by the solid phase. Finally, all Ni-FH samples exhibited phase transformation under the reaction conditions tested; however, magnetite (MG) and a green rust-like phase were observed in addition to the LP-GT phases. Under all reaction conditions, the largest amount of Ni was released into solution on the first day of reaction, after which the amount in solution decreased with time due to its readsorption into the solid phase.

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