3 research outputs found
Structure Determination and Time-Resolved Raman Spectroscopy of Yttrium Ion Exchange into Microporous Titanosilicate ETS‑4
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, multistep ion exchange process. The ion exchange process
was followed using in situ time-resolved Raman spectroscopy, and the
crystal structures 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 stepwise 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,
we constructed molecular models to explain the changes in the Raman
spectrum during ion exchange. The multistep 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 O<sup>2–</sup>. Crystal structures
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
Synthesis and Characterization of Two- and Three-Dimensional Calcium Coordination Polymers Built with Benzene-1,3,5-tricarboxylate and/or Pyrazine-2-carboxylate
Two new calcium coordination polymers, [Ca<sub>3</sub>(btc)<sub>2</sub>(H<sub>2</sub>O)<sub>12</sub>] (<b>1</b>)
and [Ca<sub>2</sub>(btc)Â(pzc)Â(H<sub>2</sub>O)<sub>3</sub>] (<b>2</b>) (btc
= benzene-1,3,5-tricarboxylate, pzc = pyrazine-2-carboxylate), have
been synthesized using the hydro/solvothermal method and have been
characterized using X-ray diffraction, IR, UV–vis, thermogravimetric
analysis, and fluorescence analysis. The structure of compound <b>1</b> is a three-dimensional framework consisting of helical chains
of calcium coordination polymers, while that of compound <b>2</b> is a double layered network in which the inorganic zigzag chains
of calcium coordination polyhedra are linked by organic ligands. Both
compounds show blue fluorescence when excited with UV light. Density
functional theory calculations on electronic absorption spectra of
organic ligands and calcium coordination polymers are discussed