INOR 649

The preparation and assembly of magnetite-PVP core-shell nanocubes

Changle Chen, clchen@uchicago.edu, Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, IL 60637, Ying Xiong, xy203@mail.ustc.edu.cn, University of Science and Technology of China, Hefei, 230026, China, and Qianwang Chen, cqw@ustc.edu.cn, Division of Nanomaterials and Chemisty, Hefei National Laboratory for Physical Sciences at Microscale, University of Science & Technology of China, Hefei, 230026.

The solvothermal treatment of a water-alcohol mixed solvent solution of ferrocene ((C₅H₅)₂Fe), polyvinylpyrrolidone (PVP) and hydrogen peroxide (H₂O₂) at 230 АC gave single-crystalline magnetite nanoparticles with a relatively narrow size distribution around 48 nm. These magnetite nanoparticles exhibited almost standard cube-like shape and were coated with a thick PVP layer (~8 nm) to form magnetite-PVP core-shell structure. To directly image the dipolar assemblies by the conventional TEM, colloidal solution of magnetite nanocubes were cast and dried onto carboncoated TEM grids by a standardized procedure. It was found that these magnetite nanocubes could be assembled into flux-clusure rings due to strong magnetic dipolar attractions. The rings had one-particle annular thickness and individual nanocubes were spaced fully together. Similar one-particle-thick rings can be found in all solvents including methanol, ethanol and butanol, indicating that drying-mediated assembly is not responsible for the formation of these nanocube rings. Magnetite nanocubes with broad particle size distribution (~ 10-60 nm) were synthesized through varying experimental parameters to probe the mechanism of the assembly. And it is proposed that there is a potential barrier for the transformation from chains to rings, and only nanocubes with large size (~ 50 nm) could overcome it. Using dipole-directed assembly to form flux-closure magnetite nanocube rings provides a way for investigating the fundamental physical properties and potential applications such as ultradense information storage.

Figure 1. (a) and (b) SEM and TEM images of magnetite nanoparticles; (c) and (d) TEM images of four nanoparticles (ІЕ is the angle over which the copper grid is titled); (e) HRTEM images of individual magnetite nanocube; (f) and (g) lattice fringe and electron diffraction (ED) pattern of magnetite nanocubes recorded from the Figure (e).

Figure 1. (a) and (b)TEM images of rings assembled from magnetite nanocubes.

Nanoscience: Synthesis and Characterization
7:00 PM-10:00 PM, Tuesday, August 21, 2007 BCEC -- Exhibit Hall - B2, Poster

Division of Inorganic Chemistry

The 234th ACS National Meeting, Boston, MA, August 19-23, 2007