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.
National Creative Research Initiative Center for Oxide Nanocrystalline Materials, School of Chemical and Biological Engineering, Seoul National University, Seoul 151-744, Korea.
Kwangjin
K
An
Soon Gu
SG
Kwon
Mihyun
M
Park
Hyon Bin
HB
Na
Sung-Il
SI
Baik
Jung Ho
JH
Yu
Dokyoon
D
Kim
Jae Sung
JS
Son
Young Woon
YW
Kim
In Chan
IC
Song
Woo Kyung
WK
Moon
Hyun Min
HM
Park
Taeghwan
T
Hyeon