Structure determination and time-resolved Raman spectroscopy of yttrium ion exchange into microporous titanosilicate ETS-4
• +1
• Aaron J. Celestian,
• J. Caleb Chappell,
• Melinda J. Rucks,
• Pauline Norris
Aaron J. Celestian
Natural History Museum of Los Angeles County (NHM)
Author Profile
J. Caleb Chappell
Miami University
Author Profile
Melinda J. Rucks
State University of New York at Stony Brook
Author Profile
Pauline Norris
Western Kentucky University (WKU)
Author Profile

## Abstract

The ion exchange of yttrium, one of the five most critical rare earth elements as outlined by the U.S. Department of Energy, into ETS-4 is a dynamic, multi-step ion exchange process. The ion exchange process was followed using in situ time-resolved Raman spectroscopy, and the crystal structure of the pre-exchange and post-exchange forms were determined by single crystal X-ray diffraction. In situ Raman spectroscopy is an ideal tool for this type of study as it measures the spectral changes that are a result of molecular geometry changes at fast time intervals, even where symmetry and unit volume changes are minimally detected by X-ray diffraction. By tracking the step-wise changes in the peak positions and intensities in the spectra, where we focused primarily on the strong spectral features corresponding to titania quantum wires and three membered-ring bending and breathing modes, molecular models were constructed to explain the changes in the Raman spectrum during ion exchange. The multi-step ion exchange process started with rapid absorption of Y into the Na2 site causing titania quantum wires to kink. After this initial uptake, the exchange process slowed, likely caused by hydration coordination changes within the channels. Next, Y exchange accelerated again during which time the Y site moved closer to the framework $$\mathrm{O^{2-}}$$. Crystal structure of the maximal Y exchanged ETS-4 material were determined, and confirmed the splitting of the Y site. Inductively coupled plasma optical emission spectroscopy was also used to quantify the extent of Y exchange, and to measure if there were indications of titania leaching from the framework.