Investigating unexpected magnetism of mesoporous silica-supported Pd and PdO nanoparticles
KAUST DepartmentAdvanced Membranes and Porous Materials Research Center
Physical Sciences and Engineering (PSE) Division
Chemical Science Program
Smart Hybrid Materials (SHMs) lab
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AbstractThe 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.
SponsorsWe gratefully acknowledge support from Dong-A University, King Abdullah University of Science and Technology (KAUST), and NSF Grant DBI-1266377. We also acknowledge Bei Zhang in the Nanofabrication core lab at KAUST for his help with the magnetic measurements. The work at UCLA also leveraged the support provided by the National Science Foundation and the Environmental Protection Agency under Cooperative Agreement Number, DBI 0830117.
PublisherAmerican Chemical Society (ACS)
JournalChemistry of Materials