The Development of New NMR Methods for Studying

1
The Development of New NMR Methods for Studying
Iron and Manganese-Containing Soil MineralsC. P.
Grey (SBU), Y. Paik (SBU), K. Cole (Fairfield
Univ. REU student), U. G. Nielsen (SBU), R. J.
Reeder (SBU), M. A. Schoonen (SBU)
In an example of the role that a Center can
play in forging new collaborations and helping to
bring expertise from one discipline into a very
different one, Clare Grey (Chemistry) and
co-workers have worked with geoscientists Reeder
and Schoonen to apply NMR methodology, originally
developed to study battery materials, to study
structures and ion sorption on paramagnetic soil
minerals. Many of the minerals found in
nature contain paramagnetic ions such as Fe or
Mn, either as major constituents (e.g., in the
iron oxides and oxyhydroxides hematite and
goethite) or as impurities. These materials are
paramagnetic and are often considered difficult
to study by NMR. The team has shown, however,
that these materials are amenable to NMR studies,
if they are studied in their paramagnetic states
(i.e., above the Néel temperature for an
antiferromagnet, or above the Curie temperature
for a ferromagnet). For example, 2H MAS NMR
spectroscopy was applied to study the deuterated
form of the iron-oxyhydroxide goethite (?-FeOOD).
This material is typically an anti-ferromagnet
at room temperature, which leads to very broad
spectra. High-resolution spectra could be
obtained above the Néel temperature by raising
the sample temperature. Cation doping and/or
control of the particle size was also used to
lower the Néel temperature, so that NMR spectra
could be acquired at ambient temperatures,
allowing ion-exchange processes to be followed
under realistic environmental conditions. NMR
studies of (toxic) cation and anion binding on
these materials are now in progress. By
exploiting the hyperfine interaction, the
mechanism that causes the large NMR shifts, we
can directly determine whether the ions are
directly bound to the mineral, or whether they
are held in a outer-sphere complex (i.e.,
surrounded completely by waters of hydration).
CHE-0221934
http//www.cems.stonybrook.edu
Center for Environmental Molecular Science