Isotope-Edited Fourier Transform Infrared Spectroscopy in Elucidating Surface Organic Species for Applications in Energy and Materials Science

Organic reagents are commonly employed in making a wide
range of
materials and play crucial roles in enabling their activities or performances.
However, the identity of organics in the final stages of active species
is challenging to characterize, and the mechanisms of organics in
active
material development are difficult to understand due to limited techniques
available at the heterogeneous interface of organic and inorganic
phases. Hence, we present a study using isotope-edited FT-IR to elucidate
the specific groups contributing to an IR marker band and shed light
on the transformation mechanisms. The molecular source of the marker
band at 1710 cm–1 was identified as a crucial problem
for improving the activity of a propietary material under commercial
development. This IR marker band was presumably a result of the orgnic
molecules oleic aicds or oleylamine during synthesis. However, the
prevailing hypotheses on the existing carbonyls from oleic acids or
from the oxidation of most likely α-carbons of the oleylamine
as the cause of the IR marker were ruled out using 1-13C-isotope-labeled compounds. Suprisingly, the marker band was found
to be associated with the remaining 17 carbons in oleic acids or oleylamine
(most likely the olefinic double bonds), confirmed by the IR shift
due to specific isotope labels at these positions. We demonstrate
that isotope-edited FT-IR is a powerful technique in characterizing
surface organic species on active materials, catalysts, or porous
media materials with broad applications in energy and materials sciences.