A XAS
A XAS study of the structural changes undergone by amorphous copper sulfides when precipitated from solution
Amorphous copper sulfide precipitates, synthesised from Cu(NO3)2 solution and H2S/Na2S, have been studied by XAS. They all contain Cu(I) and age to covellite, but their initial form depends on the concentration of the Cu(II) solution. Low concentration solutions give rise to a brown sol, which contains trigonally coordinated Cu(I), while more concentrated solutions produce a black floc, which has a close CuCu interaction of 2.66 Å similar to that in anilite, Cu7S4 and low chalcocite, Cu2S.
Due to its bright yellow-to-red emission, europium doped Ca2SiS4 is a very interesting material for phosphor converted light emitting diodes. The emission spectrum is highly dependent on the Eu concentration and can consist of more than one emission band. We combined X-ray absorption fine structure and photoluminescence measurements to analyze the structure of europium centers in (Ca,Eu)2SiS4 luminescent powders. This paper provides an explanation for the concentration dependency of the emission spectra. We find that at low dopant concentrations a large fraction of trivalent europium ions is unexpectedly present in the powders. These trivalent europium ions tend to form defect clusters in the luminescent powders. Furthermore we observe a preferential substitution of the europium ions over the two different substitutional Ca sites, which changes upon increasing the dopant concentration. At high dopant concentration, the powder crystallizes in the monoclinic Eu2SiS4 structure. Once more a preferential substitution of the europium ions is observed. Summarizing, the influence of the concentration on the emission spectrum is explained by a difference in preferential occupation of the Eu ions in the lattice.
Microchemical Journal
Volume 81, Issue 1, August 2005, Pages 50-56
An XAS study of the binding and reduction of Au(III) by hop biomass
Author links open overlay panelM.L.LópezaJ.L.Gardea-Torresdeyab
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https://doi.org/10.1016/j.microc.2005.01.011Get rights and content
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Previous studies have shown that hop biomass is capable of adsorbing significant amounts of Au(III) from aqueous solutions. Hop biomass was chemically modified to determine the contributions that the different functional groups on the biomass have on the binding and reduction of Au(III). Previously, performed batch studies showed that Au(III) binding is fast, occurring within the first 5 min of contact and in a pH dependent manner. However, esterified hop biomass behaved in a pH independent manner and the binding was found not to change with changing pH. However, the hydrolyzed biomass had a similar Au(III) binding to the native hops biomass, showing a pH dependent binding trend. X-ray absorption spectroscopy (XAS) analysis, XANES (X-ray absorption near edge structure), and EXAFS (extended X-ray absorption fine structure) were used to determine the oxidation state, coordination environment, and the average radii of the gold nanoparticles bound to the hops biomass. The XAS data confirmed the presence of Au(0) in both the native and chemically modified hop biomasses. XANES fittings show that the Au(III) was reduced to Au(0) by approximately 81%, 70%, and 83% on the native, esterified, and hydrolyzed hop biomass, respectively. In addition, the calculation of the particle radius was also in agreement with the results of previously performed transmission electron microscopy studies. The average particle could only be calculated for the native and esterified hops biomass, which showed average particle radii of 17.3 Å and 9.2 Å, respectively.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Volume 619, Issues 1–3, 1–21 July 2010, Pages 276-279
Topical Review
An XAS study of zinc speciation in aqueous acetate solutions at 25–200 °C
Author links open overlay panelStacey J.BorgabWeihuaLiua
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https://doi.org/10.1016/j.nima.2009.10.170Get rights and content
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Solutions of zinc(II) acetate in acetic acid/sodium acetate buffer solutions of varying concentration were examined by X-ray absorption spectroscopy (XAS) at temperatures between 25 and 200 °C. The influence on speciation by increasing the ratio of available acetate to Zn concentration was marked, and followed a similar trend to that observed with increasing temperature. End-member X-ray absorption spectra were observed at both the low and high temperature/acetate concentration regimes. Fitting of the EXAFS spectra gave Zn–O bonding distances in the range 1.95–2.05 Å, which are comparable to available crystallographic data. Thermodynamic modelling of the XANES data shows ZnAc+ is important at lower acetate concentration, while ZnAc2(aq) predominates solutions with acetate concentrations above 1.5 m at 25 °C, and the evolution of the XANES spectra shows that ZnAc2(aq) becomes more important with increasing temperature. Therefore acetate has been shown to be a valid Zn transport ligand under hydrothermal conditions.