Search results for "absorption spectroscopy"
showing 10 items of 828 documents
Optimization of selenium determination in human milk and whole blood by flow injection hydride atomic absorption spectrometry.
1998
abstract A flow injection hydride atomic absorption spectrometry (FI-HAAS) method was developed for determining selenium in human milk and whole blood after microwave digestion of the sample. The sample (2 mL human milk or 0.25 mL blood) was introduced into the microwave vessel with 1.5 mL HN03 and 0.25 mL H202 and 300 W (4 min) and 600 W (4 min) were applied. The digestion was completed by heating to 140 C (2-3 h). Se (VI) was reduced to Se (IV) with hydrochloric acid. The instrumental conditions for FI-HAAS (concentrations of reducing agent and carrier acid, flow rate of argon carrier gas, and sample volume injected) were optimized. The detection limit of the proposed method was 0.23 ng/m…
Multichannel multiple scattering calculation ofL2,3-edge spectra ofTiO2andSrTiO3: Importance of multiplet coupling and band structure
2010
We report a theoretical study on x-ray absorption spectroscopy at the Ti-${L}_{2,3}$-edge of rutile and anatase ${\text{TiO}}_{2}$ as well as ${\text{SrTiO}}_{3}$. Using the first-principles multichannel multiple-scattering method, we obtain good agreement with experiment in all cases. We show that both multiplet-type electron correlation effects and the long-range band structure strongly influence the spectra. The differences in line shape between the three compounds are essentially a long-range effect which reflects the different crystal structures on a length scale of 1 nm.
Photocatalytic activity of anatase-nickel ferrite heterostructures
2015
The simple co-precipitation route was used to couple commercial TiO2 anatase nanopowder with nickel ferrite (NiFe2O4). The morphology and the crystalline structure of composite nanoparticles were characterised by TEM, N2 adsorption-desorption, XRD and Rietveld refinement, XPS and XAS. The optical and magnetic properties were investigated. After co-precipitation NiFe2O4 nanoparticles, composed of spinel ferrite crystal phase, were formed on the surface of TiO2 anatase nanopowder. The TiO2/NiFe2O4 composite oxide demonstrated large specific surface area, high visible light absorption efficiency and efficient charge carrier separation, compared to pristine anatase TiO2 or pristine NiFe2O4, rep…
Physicochemical characterization of metal hexacyanometallate–TiO2composite materials
2015
The paper describes the synthesis and characterization of novel TiO2–metal hexacyanometallates (MHCMs) composite materials. The starting material, TiO2, was modified by addition of cobalt-hexacyanoferrate (CoHCF) or iron-hexacyanocobaltate (FeHCC) at various concentrations. The resulting composites were characterized as follows: cyclic voltammetry (CV) followed the formation of TiO2–MHCM clusters, TEM micrographs studied their morphology, XAS and XPS data indicated that MHCM bonds to TiO2 through the nitrogen atom of its –CN group and modifies the environment of Ti compared to that of pure anatase. As expected, and confirmed by UV-Vis and XP-valence band data, the electronic properties of T…
Dynamics of F-center annihilation in thermochemically reduced MgO single crystals
2001
Optical absorption measurements were used to monitor the thermal annihilation of oxygen vacancies (F-centers) in thermochemically reduced MgO crystals. The annihilation characteristics were sample-dependent and varied strongly with the F-center concentration. Different mechanisms for the destruction of F centers are suggested depending on their concentration.
Determination of antimony in drinking waters by an inexpensive, reproducible hydride generator for atomic spectroscopy.
1991
A method for determining antimony in drinking waters is described. In order to prevent a substantial error caused by the different oxidation states of antimony, Sb(V) is reduced to Sb(III) with potassium iodide-ascorbic acid. Covalent hydride is generated with a home made device by adding NaBH4. The hydride is then atomized in a flame-heated silica tube and atomic absorption is measured spectrophotometrically. The optimal conditions for this determination are discussed and interference effects are described. Results obtained by determining linearity range (0-200 ng), detection (LOD) and quantitation (LOQ) limits (LOD = 0.347 ng/ml, LOQ = 1.158 ng/ml), precision (instrumental CV 4.08% and me…
Towards the understanding at the molecular level of the structured-water absorption and fluorescence spectra: a fingerprint of π-stacked water
2013
An intriguing absorption peak around ∼270 nm (4.59 eV) has been recurrently recorded in aqueous solutions of salts, sugars, amino acids, in the free-solute zone (exclusion zone) adjacent to various hydrophilic surfaces, as well as a transient in the conversion process of ice to water. The corresponding associated fluorescence has been observed in the interval 480–490 nm (2.58–2.53 eV). The spectroscopic features have been related to the presence of structured water but its nature remains incompletely understood. On the basis of high-level ab initio computations, the main absorption feature of structured water is assigned to the presence of two π-stacked ground-state water molecules, prefera…
Theoretical electronic spectra of 2-aminopurine in vapor and in water
2006
The accurate quantum chemical CASSCF and CASPT2 methods combined with a Monte Carlo procedure to mimic solvation effects have been used in the calculation of the spectroscopic properties of two tautomers of 2-aminopurine (2AP). Absorption and emission spectra have been simulated both in vacuum and in aqueous environment. State and transition energies and properties have been obtained with high accuracy, leading to the assignment of the most important spectroscopic features. The lowest-lying 1 (,*) ( 1 La) state has been determined as responsible for the first band in the absorption spectrum and also for the strong fluorescence observed for the system in water. The combined approach used in …
Photoassisted Oxidation of the Recalcitrant Cyanuric Acid Substrate in Aqueous ZnO Suspensions
2007
The photoassisted oxidative transformation of the highly recalcitrant cyanuric acid was examined in the liquid−solid regime at pH 3 and natural pH 7.5 under UV irradiation in oxygen- and ozone-saturated ZnO suspensions using ZnO as a photomediator. Loss of cyanuric acid was assayed by HPLC UV absorption spectroscopy, whereas intermediates and final products were determined by HPLC ion chromatography (IC), by MS techniques using an electrospray ionization mass spectrometer operated in the negative-ion mode, and by FT-IR spectroscopy. Final reaction products were CO2 gas and NO3- ions. The measure of nitrate in solution quantified the degree of mineralization of the substrate; its concentrati…
Symbiosis between photoactive nanoparticles and their organic ligands.
2013
Photoactive spherical metal and semiconductor nanoparticles (NPs) are smart systems that exhibit unique properties, such as a high surface-to-volume ratio, a broad absorption spectrum and size-dependent properties. They are capped with a considerable number of ligands required to give rise to stable organic and aqueous NP colloidal solutions. In addition, the ligands can also be used to introduce functionality at the NP periphery. In this case, the NP could act as a 3D-scaffold, which would make a high local concentration of a functional moiety at the NP periphery possible, moreover, the photophysical properties of the NP could be tuned. The combined action of the organic capping and the in…