Sulfur Speciation in Biochars by Very High Resolution Benchtop Ka X-Ray Emission Spectroscopy

Singfoong Cheah, William Holden, Gerald Seidler

Research output: Contribution to journalArticlepeer-review

25 Scopus Citations


The analytical chemistry of sulfur-containing materials poses substantial technical challenges, especially due to the limitations of 33S NMR and the time-intensive preparations required for wet-chemistry analyses. A number of prior studies have found that synchrotron-based X-ray absorption near edge structure (XANES) measurements can give detailed speciation of sulfur chemistry in such cases. However, due to the obvious access limitations, synchrotron XANES of sulfur cannot be part of routine analytical practice across the chemical sciences community. Here, in a study of the sulfur chemistry in biochars, we compare and contrast the chemical inferences available from synchrotron XANES with that given by benchtop, extremely high resolution wavelength-dispersive X-ray fluorescence (WD-XRF) spectroscopy, also often called X-ray emission spectroscopy (XES). While the XANES spectra have higher total information content, often giving differentiation between different moieties having the same oxidation state, the lower sensitivity of the S Ka XES to coordination and local structure provides pragmatic benefit for the more limited goal of quantifying the S oxidation state distribution. Within that constrained metric, we find good agreement between the two methods. As the sulfur concentrations were as low as 150 ppm, these measurements provide proof-of-principle for characterization of the sulfur chemistry of biochars and potential applications to other areas such as soils, batteries, catalysts, and fossil fuels and their combustion products.
Original languageAmerican English
Pages (from-to)5153-5161
Number of pages9
JournalJournal of Physical Chemistry A
Issue number23
StatePublished - 2018

NREL Publication Number

  • NREL/JA-5100-71758


  • biochars
  • spectroscopy
  • sulfur chemistry


Dive into the research topics of 'Sulfur Speciation in Biochars by Very High Resolution Benchtop Ka X-Ray Emission Spectroscopy'. Together they form a unique fingerprint.

Cite this