posted on 2015-01-13, 00:00authored byHyon-Min Song, Jeffrey I. Zink, Niveen M. Khashab
The synthesis and magnetic behavior
of matrix-supported Pd and
PdO nanoparticles (NPs) are described. Mesoporous silica with hexagonal
columnal packing is selected as a template, and the impregnation method
with thermal annealing is used to obtain supported Pd and PdO NPs.
The heating rate and the annealing conditions determine the particle
size and the phase of the NPs, with a fast heating rate of 30 °C/min
producing the largest supported Pd NPs. Unusual magnetic behaviors
are observed. (1) Contrary to the general belief that smaller Pd NPs
or cluster size particles have higher magnetization, matrix-supported
Pd NPs in this study maintain the highest magnetization with room
temperature ferromagnetism when the size is the largest. (2) Twin
boundaries along with stacking faults are more pronounced in these
large Pd NPs and are believed to be the reason for this high magnetization.
Similarly, supported PdO NPs were prepared under air conditions with
different heating rates. Their phase is tetragonal (P42/mmc) with cell parameters of a = 3.050 Å and c = 5.344 Å, which are slightly larger than in the
bulk phase (a = 3.03 Å, c =
5.33 Å). Faster heating rate of 30 °C/min also produces
larger particles and larger magnetic hysteresis loop, although magnetization
is smaller and few twin boundaries are observed compared to the supported
metallic Pd NPs.