Synthesis of uniform hollow oxide nanoparticles through nanoscale acid etching.
We synthesized various hollow oxide nanoparticles from as-prepared MnO and iron oxide nanocrystals. Heating metal oxide nanocrystals dispersed in technical grade trioctylphosphine oxide (TOPO) at 300 degrees C for hours yielded hollow nanoparticles retaining the size and shape uniformity of the original nanocrystals. The method was highly reproducible and could be generalized to synthesize hollow oxide nanoparticles of various sizes, shapes, and compositions. Control experiments revealed that the impurities in technical grade TOPO, especially alkylphosphonic acid, were responsible for the etching of metal oxide nanocrystals to the hollow structures. Elemental mapping analysis revealed that the inward diffusion of phosphorus and the outward diffusion of metal took place in the intermediate stages during the etching process. The elemental analysis using XPS, EELS, and EDX showed that the hollow nanoparticles were amorphous metal oxides containing significant amount of phosphorus. The hollow nanoparticles synthesized from MnO and iron oxide nanocrystals were paramagnetic at room temperature and when dispersed in water showed spin relaxation enhancement effect for magnetic resonance imaging (MRI). Because of their morphology and magnetic property, the hollow nanoparticles would be utilized for multifunctional biomedical applications such as the drug delivery vehicles and the MRI contrast agents.
An
Kwangjin
K
National Creative Research Initiative Center for Oxide Nanocrystalline Materials, School of Chemical and Biological Engineering, Seoul National University, Seoul 151-744, Korea.
Kwon
Soon Gu
SG
Park
Mihyun
M
Na
Hyon Bin
HB
Baik
Sung-Il
SI
Yu
Jung Ho
JH
Kim
Dokyoon
D
Son
Jae Sung
JS
Kim
Young Woon
YW
Song
In Chan
IC
Moon
Woo Kyung
WK
Park
Hyun Min
HM
Hyeon
Taeghwan
T