P K-Edge XANES Calculations of Mineral Standards: Exploring the Potential of Theoretical Methods in the Analysis of Phosphorus Speciation

Abstract

Phosphorus K-edge X-ray absorption near-edge structure(XANES)spectroscopy is a technique routinely employed in the qualitativeand quantitative analysis of phosphorus speciation in many scientificfields. The data analysis is, however, often performed in a qualitativemanner, relying on linear combination fitting protocols or simplecomparisons between the experimental data and the spectra of standards,and little quantitative structural and electronic information is thusretrieved. Herein, we report a thorough theoretical investigationof P K-edge XANES spectra of NaH2PO4 & BULL;H2O, AlPO4, & alpha;-Ti(HPO4)(2)& BULL;H2O, and FePO4 & BULL;2H(2)O showingexcellent agreement with the experimental data. We find that differentcoordination shells of phosphorus, up to a distance of 5-6 & ANGS; from the photoabsorber, contribute to distinct features inthe XANES spectra. This high structural sensitivity enables P K-edgeXANES spectroscopy to even distinguish between nearly isostructuralcrystal phases of the same compound. Additionally, we provide a rationalizationof the pre-edge transitions observed in the spectra of & alpha;-Ti(HPO4)(2)& BULL;H2O and FePO4 & BULL;2H(2)O through density of states calculations. These pre-edge transitionsare found to be enabled by the covalent mixing of phosphorus s andp orbitals and titanium or iron d orbitals, which happens even thoughneither metal ion is directly bound to phosphorus in the two systems.Calculating a P K-edge XANES spectrumwith the FDMNES programstarting from a crystallographic structure leads to excellent agreementwith the experimental data and DOS calculations that enable accurateinterpretation of the observed transitions.

Published in

Inorganic Chemistry
2023, volume: 62, number: 28, pages: 11188-11198
Publisher: AMER CHEMICAL SOC

SLU Authors

• Persson, Ingmar

  • Department of Molecular Sciences, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Inorganic Chemistry

Publication identifier

• DOI: https://doi.org/10.1021/acs.inorgchem.3c01346

Permanent link to this page (URI)

https://res.slu.se/id/publ/122933