Tuning the Magnetism of Plasma-Synthesized Iron Nitride Nanoparticles: Application in Pervaporative Membranes

The present work
reports on the low-pressure, radio-frequency,
plasma-driven synthesis of ε-Fe3N-type nanoparticles
homogeneously deposited on a high-surface-area porous carbon support,
with tunable magnetic properties, directly depending on the plasma
treatment conditions. Iron nanoparticles are formed from the degradation
of a solid organometallic precursor mixed with a carbon xerogel in
a nitrogen-containing (argon/ammonia) plasma discharge. Variation
of the working pressure during the plasma treatment directly affects
the residence time of the reactive species, which determines the crystalline
state of the nanoparticles, from amorphous at low-pressure treatment
to well crystallized at high-pressure treatment. This results in a
direct influence of the magnetic properties of the iron nitride nanoparticles.
The working pressure results in two competing effects because it enhances
the crystallinity (at higher pressure) and also slightly affects the
surface chemistry of the nanoparticles by increasing the oxygen content,
while the last is believed to deteriorate the magnetic properties;
however, the crystallinity enhancement dominates. The synthesized
FexN/CXG magnetic composites
have been applied as filler materials in alginate membranes for ethanol
dehydration in a pervaporation experiment. Results indicate a considerably
enhanced performance of the alginate membrane as determined by its
selectivity, the separation index, and the flux even when using a
small FexN/CXG loading (3%
w/w).