Jeffrey Cutler

Organic carbon and sulphur compounds in wetland soils: insights on structure and transformation processes using K-edge XANES and NMR spectroscopy

Abstract X-ray absorption near-edge structure (XANES) and nuclear magnetic resonance (NMR) spectroscopy were used in combination to characterize organic carbon structures in a series of wetland soils in Saskatchewan, and XANES spectroscopy was also used to examine sulphur speciation in the soils. The organic C contents of most of the wetland soils are consistently higher by a factor of two to five times compared to adjacent well-drained soils. NMR analyses indicate that the organic matter in the wetland soils consists of predominantly aliphatic structures such as carbohydrates and long chain poly(methylene) units which are refractory structures found in plant waxes. The poly(methylene) structures have a significant capacity to sorb nonpolar organic molecules. The phenolic OH and carboxyl group content of the wetland soils studied is an additional significant factor in their sequestering ability for heavy metals or pesticides. Carbon XANES spectroscopy shows that the surface (∼10 nm) layer of particulate organic matter has a structure dominated by aromatic, carbohydrate and carboxylic acid-like material apparently derived from partially degraded lignin and cellulose polymers which are adsorbed onto clay minerals. The aliphatic structures remaining in this surface layer are probably recalcitrant (poly)methylene units. At a depth of ∼100 nm, the aliphatic content significantly increases suggesting the presence of more labile structures. The presence of these more labile aliphatic compounds may be due to slow decomposition rates in the wet, often cool environments present and to the protective action of the more refractory components in the surface ∼10 nm of the organic matter. Drying of the wetlands, either by draining or as a result of climate change, is likely to result in the rapid decomposition of these labile organic structures releasing carbon dioxide. Our data indicate that the preservation of the organic carbon compounds in these soils is a result of their presence as surface adsorbed layers on the soil mineral particles. The soils contain three different classes of sulphur compounds: reduced organic sulphur such as sulphides, low valent oxidized sulphur such as sulphoxides, and high valent oxidized sulphur such as sulphonate and sulphate. Of these, reduced sulphur species constitute between one-third and two-thirds of the total. Sulphonate structures comprise between a fifth and a third of the total. Sulphates exhibit a wide variation in content, and sulphoxides are either not detected or are present to a lesser extent (

Electronic structure of TiO2 nanotube arrays from X-ray absorption near edge structure studies

We report an X-ray absorption near edge structure (XANES) investigation of several TiO2nanotube arrays, including the as-prepared nanotube arrays from electrochemical anodic oxidation of Ti foil (as-prepared ATNTA), as-prepared nanotube arrays after annealing at 580 °C (annealed ATNTA) and annealed ATNTA after electrochemical intercalation with Li (Li-intercalated ATNTA). XANES at the O K-edge and Ti L3,2 and K edges shows distinctly different spectral features for the as-prepared and the annealed ATNTA, characteristic of amorphous and anatase structures, respectively. Intercalation of Li into annealed ATNTA induces a surprising, yet spectroscopically unmistakable, anatase to rutile transition. XANES at the Li K-edge clearly shows ionic features of Li in ATNTA. The charge relocation from Ti 3d to O 2p at the conduction band in TiO2 was also observed when Li ions were intercalated into annealed ATNTA albeit no noticeable reduction of Ti4+ to Ti 3+ was observed. The O K-edge shows a distinctly enhanced feature in the multiple scattering regime, indicating a close to linear O–Li–O arrangement in Li-intercalated ATNTA. These results show bonding changes between Ti and O resulting from the interaction of Li ions in the TiO2 lattices. Such bonding variation has also been supported by X-ray excited optical luminescence (XEOL), which suggests Li+-defect interactions. The implications of these results are discussed.

Synchrotron micro-X-ray fluorescence analysis of natural diamonds : First steps in identification of mineral inclusions in situ

Abstract Diamond inclusions are of particular research interest in mantle petrology and diamond exploration as they provide direct information about the chemical composition of upper and lower mantle and about the petrogenetic sources of diamonds in a given deposit. The objective of the present work is to develop semi-quantitative analytical tools for non-destructive in situ identification and characterization of mineral inclusions in diamonds using synchrotron micro-X-ray Fluorescence (μSXRF) spectroscopy and micro-X-ray Absorption Near Edge Structure (μXANES) spectroscopy at a focused spot size of 4 to 5 micrometers. The data were collected at the Pacific Northwest Consortium (PNC-CAT) 20-ID microprobe beamline at the Advanced Photon Source, located at the Argonne National Laboratory, and yielded the first high-resolution maps of Ti, Cr, Fe, Ni, Cu, and Zn for natural diamond grains, along with quantitative μSXRF analysis of select chemical elements in exposed kimberlite indicator mineral grains. The distribution of diamond inclusions inside the natural diamond host, both visible and invisible using optical transmitted-light microscopy, can be mapped using synchrotron μXRF analysis. Overall, the relative abundances of chemical elements determined by μSXRF elemental analyses are broadly similar to their expected ratios in the mineral and therefore can be used to identify inclusions in diamonds in situ. Synchrotron μXRF quantitative analysis provides accurate estimates of Cr contents of exposed polished minerals when calibrated using the concentration of Fe as a standard. Corresponding Cr K-edge μXANES analyses on selected inclusions yield unique information regarding the formal oxidation state and local coordination of Cr.

X-ray techniques for innovation in industry

Are synchrotrons needed for innovation in industry? What can scientists at large-scale facilities offer for R&D in industry? Is the comfort of life profiting from research?

Industrial Science at the Canadian Light Source: Access, Services, and Strategies

Since the concept of a synchrotron research facility in Canada in the mid-1990s, utilization by industry has been a pillar that has made the Canadian Light Source (CLS) unique in the global synchrotron community. With few synchrotron facilities working with the private sector in 1995, the relevance of a highly active industrial science program was questioned by many stakeholder groups, but as the CLS proposal was being developed, it became abundantly clear that for a synchrotron to be successful in Canada, it would need the support of both academia and industry; a dedicated industrial science group therefore became an integral part of the CLS.

Raman Spectroscopy in the Hydrometallurgical and Materials Engineering World

Autoclave processing of arsenical sulphide feedstocks from which precious metals (Cu, Co, Zn, Ni, Au) are extracted from employs high temperatures (150-225°C) which produces Fe-AsO4-SO4 crystalline phases [1-2]. In 1994, four phases were reported to form for the high temperature (150-225°C) Fe-AsO4-SO4 system [2] but confusion arose in 2007, as the discovery of two new phases were reported [3]. Therefore it was evident that these phases had not been fully identified in terms of arsenate speciation, in spite of the fact that some of these phases are used and advocated in arsenic disposal [2-3]. In the second case, attempts to increase the throughput (extraction of Zn) of an industrial leach autoclave, a massive scale formation never before observed resulted in halting of production. The final case deals with the binding mechanism between the highly commercialized N719 molecule and nano-crystalline anatase (TiO2) as a semiconductor in the DSSC field which has been highly investigated over the last decades [4-5] as a result of the high efficiencies they produce.

XAFS of Synthetic Iron(III)‐Arsenate Co‐Precipitates and Uranium Mill Neutralized Raffinate

XAFS studies were carried out for chemical speciation of arsenic species in uranium mill neutralized raffinate solids. To aid the structural characterization, synthetic iron(III)‐arsenate co‐precipitates were prepared to mimic the actual uranium mill tailings neutralization products. The principle components analysis method was used to validate the synthetic amorphous scorodite as a primary model compound for arsenate species in the raffinate samples under the specific precipitation conditions.