An unexpected phase transformation of ceria nanoparticles in aqueous media.

Cerium oxide Nanoparticles (CNPs) are of significant interest to the scientific community due to their wide spread applications in a variety of fields. It is proposed that size dependent variations in the extent of Ce3+ and Ce4+ oxidation states of cerium in CNPs determines the performance of CNPs in application environments. To obtain greater molecular and structural understanding of chemical state transformations previously reported for ceria ≈ 3 nm nanoparticles (CNPs) in response to changing ambient conditions, microXRD and Raman measurements were carried out for various solution conditions.

Ultraviolet (UV) Raman spectroscopy study of the Soret effect in high-pressure CO2-water solutions.

Spatially resolved deep-ultraviolet (UV) Raman spectroscopy was applied to solutions of CO(2) and H(2)O or D(2)O subject to a temperature gradient in a thermally regulated high-pressure concentric-tube Raman cell in an attempt to measure a Soret effect in the vicinity of the critical point of CO(2). Although Raman spectra of solutions of CO(2) dissolved in D(2)O, at 10 MPa and temperatures near the critical point of CO(2), had adequate signal-to-noise and spatial resolution to observe a Soret effect with a Soret coefficient with magnitude |S(T)| > 0.03, no evidence for an effect of this size was obtained for applied temperature gradients up to 19 °C.

Following 18O uptake in scCO2-H2O mixtures with Raman spectroscopy.

The uptake of (18)O by scC(16)O(2) in mixtures containing liquid H(2)(18)O was followed with Raman spectroscopy using a specially designed high-pressure optical cell. Characteristic bands from the C(16)O(18)O and C(18)O(2) molecules were identified in the supercritical phase and measured in the spectra as a function of time after introducing the liquid H(2)(18)O into the scC(16)O(2). Temporal dependence indicated the process was diffusion-limited in our cell for both C(16)O(18)O and C(18)O(2).

Raman spectrum of supercritical C(18)O2 and re-evaluation of the Fermi resonance.

We report the first Raman spectra of fully (18)O-labeled supercritical CO(2) (scCO(2)) and various isotopic mixtures. The experimental results, coupled with ab initio molecular dynamics calculations, demonstrate that the frequencies assigned to the Fermi dyad of the CO(2) molecule transpose upon isotopic labeling of both oxygen atoms. Although the transposition of the Fermi dyad of CO(2) gas due to isotopic substitution has been discussed before, this is the first confirmation of the effect in the Raman spectrum of the supercritical fluid and provides necessary groundwork for future Raman spectroscopy studies of reactions in this important medium.

Competitive adsorption study of CO2 and SO2 on CoII3[CoIII(CN)6]2 using DRIFTS.

Diffuse reflectance infrared Fourier transform spectroscopy was used to study the competitive adsorption of CO(2) and SO(2) on the cobalt Prussian blue analogue Co(II)(3)[Co(III)(CN)(6)](2) at 298 K. Characteristic peaks for adsorbed CO(2) and SO(2) species were identified and their relative areas, measured simultaneously as a function of pressure at 298 K, varied in accordance with a Langmuir-Freundlich isotherm fitted to both gases in the low-coverage Henry's Law limit. Evidence for co-adsorption of trace water was also obtained, as well as the apparent formation of an analogous cobalt nitroprusside compound as a reaction product under certain conditions.

Adsorption of CO2 on CoII3[CoIII(CN)6]2 using DRIFTS.

Adsorption of CO(2) on dehydrated Prussian blue analogue Co(II)(3)[Co(III)(CN)(6)](2) was studied using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). An infrared peak at 2340 cm(-1) assigned to adsorbed CO(2) was identified and used semi-quantitatively to construct an isotherm at 298 K that followed the Langmuir-Freundlich equation in the low-coverage Henry's law limit with CO(2) pressure below about 25 kPa. Temperature-dependence at 6.