posted on 2006-09-14, 00:00authored byChangzheng Wu, Ping Yin, Xi Zhu, Chuanzi OuYang, Yi Xie
We demonstrated in this paper the shape-controlled synthesis of hematite (α-Fe2O3) nanostructures with a
gradient in the diameters (from less than 20 nm to larger than 300 nm) and surface areas (from 5.9 to 52.3
m2/g) through an improved synthetic strategy by adopting a high concentration of inorganic salts and high
temperature in the synthesis systems to influence the final products of hematite nanostructures. The benefits
of the present work also stem from the first report on the <20-nm-diameter and porous hematite nanorods,
as well as a new facile strategy to the less-than-20-nm nanorods, because the less-than-20-nm diameter size
meets the vital size domain for magnetization properties in hematite. Note that the porous and nonporous
hematite one-dimensional nanostructures with diameter gradients give us the first opportunity to investigate
the Morin temperature evolution of nanorod diameter and porosity. Evidently, the magnetic properties for
nanorods exhibit differences compared with those for the spherical particle counterparts. Hematite nanorods
are strongly dependent on their diameter size and porosity, where the magnetization is not sensitive to the
size evolution from submicron particles to the 60−90 nm nanorods, while the magnetic properties change
significantly in the case of <20 nm. In other words, for the magnetic properties of nanorods, in a comparable
size range, the porous existence could also influence the magnetic behavior. Moreover, applications in
formaldehyde (HCHO) gas sensors and lithium batteries for the hematite nanostructures with the diameter/surface area gradient reveal that the performance of electrochemical and gas-sensor properties strongly depends
on the diameter size and Brunauer−Emmett−Teller (BET) surface areas, which is consistent with the crystalline
point of view. Thus, this work not only provides the first example of the fabrication of hematite nanostructure
sensors for detecting HCHO gas, but also reveals that the surface area or diameter size of hematite nanorods
can also influence the lithium intercalation performances. These results give us a guideline for the study of
the size-dependent properties for functional materials as well as further applications for magnetic materials,
lithium-ion batteries, and gas sensors.