Environmental Engineering Reference
In-Depth Information
nanoparticles, utilized in transfer hydrogenation reactions with isopropanol as the
hydrogen donor, as well as a series of catalytic and kinetic experiments. Presence of
nickel nanoparticles in the zero-valence state has been confirmed by EMR
experiments.
12.3.3 Gold Nanoparticles
Ionita et al. [
13
] reported characterization of ligand dynamics attached to gold
nanoparticles. EMR spectra of a series of spin labeled nanoparticles at variable
temperature and at different frequencies were recorded. Series of Au nanoparticles
protected by a monolayer of organic ligands and labeled them with disulfide
functionalized nitroxides. The chain length of the spin labels and the surrounding
ligands was systematically varied. Authors found that the rotational diffusion rate
of the spin labels increases with the length of the linker connecting the nitroxide
unit to the Au surface. They could further suggest that packing of the organic shell
also influences the diffusion parameters.
12.4 EMR of Metal Oxyhydroxide and Metal Oxide
Nanoparticles
Metal oxyhydroxide and metal oxide nanoparticles are the important class of
materials because their optical, magnetic, and electrical properties find a wide
range of technological and biomedical applications. The following section summa-
rizes some of the EMR investigations of metal oxyhydroxide and metal oxide
nanoparticles.
12.4.1 Nanoparticles of Oxyhydroxides of Iron
Akaganeite is one of the polymorphs of iron hydroxides. Fe
3+
ion in Akaganeite
nanoparticles is responsible for EMR signal. Parameshwari et al. [
14
] have
performed systematic EMR study of peak-to-peak line width and spin-spin relax-
ation time for samples prepared with different dextrose concentration. The spin-
spin relaxation process which accounts for the energy difference transferred to the
neighboring electrons is important as for as the line widths are concerned. They
have reported the spin-spin relaxation time for different concentration of dextrose
used in coprecipitation and found that relaxation time decreases with increasing
dextrose concentration. On the basis of their study of relaxation time they have
inferred that akaganeite nanoparticles may be potential candidate for microwave
