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The analytical chemistry of phosphorus-containing materials is often impeded by the long measurement times and relatively large sample masses needed for 31 P NMR spectroscopy, by the scarcity and access limitations of synchrotron beamlines operating in the energy range of the P K-edge, by the challenges posed by species interconversion during liquid extraction, and by the considerable air-sensitivity typical of many phosphorus-containing materials and nanophases. To this end, we report the design and operation of a new laboratory-based spectrometer to simultaneously perform P Kα and Kβ X-ray emission spectroscopy (XES) while being housed in a research-grade controlled-atmosphere glovebox. Demonstration studies on nickel phosphide nanophases illustrate the importance of air-free XES and the value of simultaneous Kα and Kβ spectroscopy for identifying the P oxidation state and for investigating nanoscale influences on valence level electronic structures. 

We report a comprehensive computational study of unsupervised machine learning for extraction of chemically relevant information in X-ray absorption near edge structure (XANES) and in valence-to-core X-ray emission spectra (VtC-XES) for classification of a broad ensemble of sulphorganic molecules. By progressively decreasing the constraining assumptions of the unsupervised machine learning algorithm, moving from principal component analysis (PCA) to a variational autoencoder (VAE) to t-distributed stochastic neighbour embedding (t-SNE), we find improved sensitivity to steadily more refined chemical information. Surprisingly, when embedding the ensemble of spectra in merely two dimensions, t-SNE distinguishes not just oxidation state and general sulphur bonding environment but also the aromaticity of the bonding radical group with 87% accuracy as well as identifying even finer details in electronic structure within aromatic or aliphatic sub-classes. We find that the chemical information in XANES and VtC-XES is very similar in character and content, although they unexpectedly have different sensitivity within a given molecular class. We also discuss likely benefits from further effort with unsupervised machine learning and from the interplay between supervised and unsupervised machine learning for X-ray spectroscopies. Our overall results, i.e. , the ability to reliably classify without user bias and to discover unexpected chemical signatures for XANES and VtC-XES, likely generalize to other systems as well as to other one-dimensional chemical spectroscopies. 

The evolution of sulfur chemistry in cements is best known in the bailiwick of failure mechanisms via sulfate attack, but is equally important for its contributions to the reduction capacity of cementitious materials often used for immobilizing nuclear waste streams destined for long‐term storage, for example, cementitious waste forms (CWF). The total reduction capacity of CWFs, encompassing contributions from both S and Fe reductants, and its implications toward radionuclide immobilization is most often studied by destructive wet chemistry methods requiring acid digestion in the presence of Ce(IV) and subsequent titration and colorimetric interpretation. Here, we investigate a similarly analytical but nondestructive alternative, benchtop high resolution wavelength‐dispersive X‐ray fluorescence spectroscopy, most commonly known as X‐ray emission spectroscopy (XES), for probing the bulk sulfur oxidation state distribution. We present here an initial investigation of S XES, including an improved experimental protocol for lab XES of inhomogeneous samples, both as a complement to the Ce(IV) test and for new scientific opportunities that it enables for observing changes in sulfur chemistry. We discuss future improvements and opportunities, including: (1) the practical challenges associated with coordinating XES and Ce(IV) liquid extraction for a more comprehensive perspective on reduction capacity and for a high‐precision evaluation of uncertainties in the Ce(IV) test; and (2) new opportunities, due to the nondestructive nature of XES, for controlled evolution studies aimed at elucidating specific chemical responses of CWFs exposed to invasive gas or liquid species or to accelerated aging by radiative dose or thermal treatment.

 

Generating oxygen vacancies (Vö) in vanadium pentoxide (V 2 O 5 ) has been demonstrated as an effective approach to tailor its electrochemical properties. The present study investigates three different kinds of conductive polymer (CP = PPy, PEDOT, and PANI) coated V 2 O 5 nanofibers with Vö generated at the interface during the polymerization process. Surface Vö form a local electric field and promote the charge transfer kinetics of the resulting Vö-V 2 O 5 /CP nanocables, and the accompanying V 4+ and V 3+ ions may also catalyze the redox reactions and improve the supercapacitor performance. The differences and similarities of three different CP coatings have been compared and discussed, and are dependent on their polymerization conditions and coating thickness. The distribution of Vö in the surface layer and in the bulk has been elaborated and the corresponding effects on the electrochemical properties and supercapacitor performance have also been investigated. Vö-V 2 O 5 /CP can deliver a high capacity of up to 614 F g −1 at a current rate of 0.5 A g −1 and supercapacitors with Vö-V 2 O 5 /CP demonstrated excellent cycling stability over 15 000 cycles at a rate of 10 A g −1 . 

Spherically‐bent crystal analyzers (SBCAs) see considerable use in very high‐resolution hard X‐ray wavelength dispersive X‐ray fluorescence spectroscopy, often called X‐ray emission spectroscopy (XES). While Si and Ge are the most frequently used diffractive components of SBCAs, we consider here the somewhat classical choice of muscovite mica as the dispersing element. We find that the various harmonics of a highest‐quality mica‐based SBCA show ~5–~40% of the integral reflectivity per unit solid angle of a typical Si or Ge SBCA in the hard X‐ray range, and that the mica SBCA have comparable energy resolution to the traditional SBCAs. Interestingly, the choice of mica comes with a practical benefit: the primary (0,0,2) reflection has sufficiently strong harmonics that are fairly tightly spaced in energy so that they span the complete energy range from ~4 to ~11 keV when used at convenient Bragg angles in a Rowland circle spectrometer. Hence, a single mica SBCA can be used for every K‐shell emission line of three dimensional transition metals and every L‐shell emission line of the lanthanide elements simply by selecting the correct mica (0,0,2) harmonic with a final energy‐dispersive solid state detector. The loss in efficiency is counteracted by an operational efficiency, i.e., the “universal” application of a single analyzer over a very large range of elements. This performance suggests future application of mica SBCAs in both laboratory‐based XES and synchrotron‐based photon‐in, photon‐out spectroscopies in the hard X‐ray range.