X-ray Near-edge Structure Spectroscopy Research Articles

Deciphering the Impact of ZnO Nanoparticles and a Sunscreen Product Containing ZnO on Phosphorus Dynamics and Release in Chlorella pyrenoidosa in Aquatic Systems.

Zinc oxide nanoparticles (ZnO NPs) expedite the conversion of organic phosphorus (OP) into PO4-P (Pi), facilitating phosphorus (P) absorption by algae. Our study explored the mechanisms of converting OP (2-aminoethylphosphonic acid (AEP) and β-glycerol phosphate (β-GP)) into Pi in Chlorella pyrenoidosa under P deficiency with sunscreen and ZnO NPs. Cell density followed the order of K2HPO4 > β-GP+ZnO > β-GP > AEP+ZnO > AEP > P-free. ZnO NPs promoted the conversion of β-GP, containing C-O-P bonds (0.028-0.041 mg/L), into Pi more efficiently than AEP, which possesses C-P bonds (0.022-0.037 mg/L). Transcriptomics revealed Pi transport/metabolism (phoB (3.99-12.01 fold), phoR (2.20-5.50 fold), ppa (4.49-10.40 fold), and ppk (2.50-5.40 fold)) and phospholipid metabolism (SQD1 (1.85-2.79 fold), SQD2 (2.60-6.53 fold), MGD (2.13-3.21 fold), and DGD (4.08-7.56 fold)) were up-regulated compared to K2HPO4. 31P nuclear magnetic resonance spectroscopy identified intracellular P as polyphosphate, orthophosphate, and pyrophosphate. Synchrotron radiation-based X-ray near-edge structure spectroscopy indicated that K2HPO4 and Zn3(PO4)2 in β-GP+ZnO were increased by 8.09% and 7.28% compared to AEP+ZnO, suggesting superior P storage in β-GP+ZnO. Overall, ZnO NPs improved photoinduced electron-hole pair separation and charge separation efficiency and amplified the ·OH and ·O2- levels, promoting OP photoconversion into Pi and algae growth.

Formation and Immobilization of Cr(VI) Species in Long-Term Tannery Waste Contaminated Soils

Chromium speciation in naturally contaminated soils appears more complex than spiked studies have shown. This study characterized Cr speciation (oxidation states; availability; molecular geometry) intended to highlight the genesis of immobile Cr(VI) species in long-term tannery waste-contaminated soils. In a series of samples obtained from Shuitou in China, chemical extraction methods showed that Cr(III) was dominant(>96.7% of total Cr), with Cr(VI) concentration up to 144 mg kg-1. Of the total Cr(VI) present, immobile Cr(VI) represents >90%. Synchrotron-based X-ray near-edge structure spectroscopy (XANES) showed the occurrence of Cr(VI), which was not removed by phosphate buffer extraction, confirming a significant amount of immobile Cr(VI) fractions in soils. X-ray fluorescence maps exhibited the heterogeneous distribution of Cr in soils associated with both Mn and Fe. Such a distribution suggests Cr(III) oxidation to Cr(VI) by Mn oxides and a possible immobilization of both Cr(III) and Cr(VI) onto Fe (hydr)oxides. Linear combination fitting of XANES spectra revealed that fractional weights (%) in samples were CrFeO3 (49.3-53.6), CrOOH (22.3-30.8), and CaCrO4 (13.2-25.3). Our results demonstrate that (i) Cr(VI) is immobilized in soils and (ii) mechanisms of Cr(VI) immobilization are CaCrO4 precipitation and recrystallization with Fe (hydr)oxides.

Mn-doped TiO2 photocatalysts: Role, chemical identity, and local structure of dopant

The response of TiO2 is extended to visible light by doping with Mn through a hydrothermal route. The role, chemical identity, and local structure of the Mn dopants are comprehensively elucidated to find the key factors behind the improved photocatalytic activity. X-ray absorption fine structure and X-ray near-edge structure spectroscopy with synchrotron light reveal that the Mn dopants partially replace Ti atoms in the bulk of the TiO2 host to form a MnO2–TiO2 solid solution. The Mn dopants extend the light absorption of the host to the visible region and restrict electron-hole recombination, as probed by diffuse reflectance spectroscopy and light-induced infrared absorption spectroscopy, respectively. The extension of light absorption is not monotonically correlated with the improvement in photocatalytic activity. At an excessive Mn concentration, the conduction band edge bottom becomes too low to enable the reduction of the adsorbed oxygen by the photoexcited electrons. The unconsumed electrons eventually recombine with holes to accelerate the recombination, resulting in a low electron population. There is a trade-off between the extended light absorption and the recombination. This is optimized at a Mn concentration of 4 wt%, to yield the highest electron population, and thus, the highest photocatalytic activity.

Pd-based (Ce,Zr)O x-supported catalysts: Promoting effect of base metals (Cr, Cu, Ni) in CO and NO elimination

A series of Pd–M bimetallic three-way catalysts (M = Cr, Cu and Ni) supported on a (Ce,Zr)O x material has been characterized using a combination of X-ray diffraction and Raman spectroscopy, and employing in situ diffuse reflectance Fourier transform infrared and X-ray near-edge structure spectroscopies to analyse the redox and chemical processes taking place during light-off conditions under CO, NO and O 2. The catalytic behaviour of these bimetallic systems was strongly affected by the degree of interaction between the noble and base metals in the calcined state. Among the base metals tested, Ni appeared to exert the least influence over the noble metal state/behaviour after calcination and under reaction conditions. Cr and Cu appear to interact with Pd in the calcined state, leading to a reduction in the temperature at which Pd was converted to Pd(0) with simultaneous formation of a binary PdM alloy during the reaction run. At high temperature, these alloy phases evolved into pure metallic Pd(0) particles and, in the case of the Cu-containing catalyst, result in a strong interaction with the support. The catalytic performance of these three Pd–M systems in the CO and NO elimination reactions are correlated with the nature and properties of the oxidized and reduced Pd-containing phases which are present in each case.

Packing of the Prion Ure2p in Protein Fibrils Probed by Fluorescence X-ray Near-edge Structure Spectroscopy at Sulfur K-edge

The soluble protein Ure2p from the yeast Saccharomyces cerevisiae assembles in vitro into straight and insoluble protein fibrils, through subtle changes of conformation. Whereas the structure of soluble Ure2p has been revealed by X-ray crystallography, further characterization of the structure of insoluble Ure2p fibrils is needed. We performed X-ray absorption near-edge spectroscopy (XANES) at the sulfur K-edge to probe the state of Cys221 in the fibrillar form of Ure2pC221 and provide structural information on the structure of Ure2p within fibrils. Although the Ure2p dimer dissociation into its constituent monomers has proven to be a prerequisite for assembly into fibrils, we showed the ability of every Ure2pC221 monomer to establish disulfide bonds upon incubation of the fibrils under oxidizing conditions. Our result indicates either that the constituent unit of the fibrillar form of the protein is a dimeric Ure2p or that the fibrils are made of protofilaments assembled in such a way that the residue C221 from a Ure2p molecule in one protofilament is located in the vicinity of a C221 residue from another molecule belonging to a neighbor protofilament.

Influence of the nature of the Ce-promoter on the behavior of Pd and Pd–Cr TWC systems

A series of monometallic Pd and bimetallic Pd–Cr catalysts supported on CeO x /Al 2O 3 (CA) and (Ce, Zr)O x /Al 2O 3 (CZA) materials have been characterized using a combination of X-ray diffraction (XRD), electron microscopy, and Raman spectroscopy, and employing electron paramagnetic resonance and in situ diffuse reflectance Fourier transform infrared and X-ray near-edge structure spectroscopies to analyze the redox and chemical processes taking place under light-off conditions in a gaseous, stoichiometric mixture containing CO, NO, and O 2. The catalytic behavior of these mono and bimetallic systems was strongly affected by the nature of the cerium-containing promoter. The Pd–ceria interface appeared significantly more active than Pd–ceria/zirconia in both CO oxidation and NO reduction processes under stoichiometric conditions. This factor seems to dominate the differential behavior of Pd monometallic systems. In the case of Pd–Cr bimetallic systems, an additional strong influence of the base metal on the oxidation state of Pd appears of importance in explaining the catalytic behavior of the samples. For the CeO x /Al 2O 3 supported catalyst, the formation of Pd(0) at lower temperatures leads to an initial enhancement in activity, while formation of a Pd–Cr alloy above 473 K suppressed full NO conversion at high temperatures. These effects were absent in the (Ce, Zr)O x /Al 2O 3 supported system.

Behavior of bimetallic Pd–Cr/Al 2O 3 and Pd–Cr/(Ce,Zr)O x/Al 2O 3 catalysts for CO and NO elimination

A series of Pd–Cr bimetallic catalysts supported on a (Ce,Zr)O x /Al 2O 3 mixed support or Al 2O 3 alone have been characterized using a combination of X-ray diffraction, electron paramagnetic resonance, and Raman spectroscopy and employing in situ diffuse reflectance infra-red Fourier transform and X-ray near-edge structure spectroscopy to analyze the redox and chemical processes taking place during the course of the CO+NO+O 2 reaction. The catalytic behavior of these bimetallic systems was strongly affected by the nature of the support. In the case of the alumina support, evidence for interactions between Pd and Cr was observed in the calcined state. Under reaction conditions, formation of a mixed oxide phase containing Pd(I) and Cr(III) appears to be responsible for the improvement in CO oxidation and for the detrimental effect in the NO reduction process with respect to a monometallic, Pd reference system. In the case of the (Ce,Zr)O x /Al 2O 3 mixed support, the addition of Cr was less influential in terms of catalytic activity. Results for the latter are rationalized mainly on the basis of the absence of interaction between the metal components in the calcined state and the presence of surface entities containing Cr alone when metallic-like Pd particles are formed during the course of reaction.

EXAFS studies on erbium-doped TiO 2 and ZrO 2 sol–gel thin films

High concentration (15% in a molar ratio) Er-doped TiO 2 and ZrO 2 sol–gel layers, annealed under an oxygen flow, at 300 and 650 °C, respectively, were studied at the erbium L III edge (8358 eV) by X-ray near edge structure spectroscopy (XANES) and extended X-ray absorption fine structure spectroscopy (EXAFS) in order to obtain some useful information about the local atomic arrangement around the incorporated rare earths. Transmission electronic microscopy (TEM) experiments were also carried out in order to support the X-ray absorption spectroscopy (XAS) studies by a knowledge of the global structure of the sol–gel layer. The analysis of the XAS data reveals that, in the case of an annealing treatment at 300 °C, the local atomic structure surrounding the erbium ion appears amorphous for both samples, while after an annealing treatment at 650 °C, a crystalline structure around the dopant is strongly dependent on the nature of the lattice cation (Ti or Zr). Indeed, for such an annealing temperature, the local atomic environment around the erbium ion appears to be amorphous in the case of an anatase matrix while it seems to have crystallized around the dopant in the case of zirconia. Furthermore, for both these compounds the XAS data reveal that a pairing effect between the erbium ions probably occurs. The TEM studies performed on the samples annealed at 650 °C show the appearance of other phases different from the matrix, confirming this fact. For both compounds, the analysis of these sets of data reveals that the erbium ion has not formed metallic erbium in the matrix. For the Er-doped TiO 2 sol–gel layers, it can be concluded that the rare earth has not precipitated in the form of erbium oxide clusters. Whereas, for the Er-doped ZrO 2 sol–gel layers, nothing can be deduced about the possible appearance of Er 2O 3. It can be then concluded that the appearance of another phase, with the formula near Zr 3Er 4O 12, likely occurs in the case of the Er-doped ZrO 2 sol–gel layer annealed at 650 °C, while a solid solution of Er x Ti y O z was formed in the case of the Er-doped TiO 2 sol–gel layer (annealed at 650 °C). Nevertheless it should be noted that the high concentration of erbium doping used on this study (15%) is not the one which presents the most useful interest for applications as optical devices. Such a high concentration of erbium, selected for the XAS measurement, provides a clue to the chemical mechanisms which could explain the optical properties of the rare earth shown in former studies.