Synthesis of Hematite (α-Fe₂O₃) Nanorods:  Diameter-Size and Shape Effects on Their Applications in Magnetism, Lithium Ion Battery, and Gas Sensors

Abstract

We demonstrated in this paper the shape-controlled synthesis of hematite (alpha-Fe(2)O(3)) 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 m(2)/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.

Synthesizing Iron Oxide Nanostructures: The Polyethylenenemine (PEI) Role

“…In fact, the low initial value of 250 K and the large spread up to 300 K is consistent with the formation of small-sized (<50 nm) hematite domains, which act as a secondary phase to the main one of magnetite [30]. Conversely, no such a trend can be observed in the FeO_nopei sample, where the disappearance of the Morin transition suggests the formation of hematite domains smaller than 20 nm [31]. No superimposition of the ZFC and FC magnetization curves can be observed for any of the samples, which implies that the NPs are still in a blocked state at 400 K and that no superparamagnetic relaxation can be observed within the experimental thermal range (Figure 5a).…”

High-surface-area α-Fe2O3/carbon nanocomposite: one-step synthesis and its highly reversible and enhanced high-rate lithium storage properties

“…[4][5][6] As one of the promising anode materials, hematite (a-Fe 2 O 3 ) has been investigated intensively due to its great advantages such as high theoretical capacity (1007 mAh g À1 ), low cost, good stability, environmental friendliness, and high resistance to corrosion. [7][8][9][10][11][12][13][14][15] Recently, the capacity retention of iron oxide can be improved via fabricating active materials into hollow/nano-structures which could accommodate volume changes and shorten the lithium diffusion length. 9,[11][12][13][14] Furthermore, a selected binder, sodium carboxymethyl cellulose (CMC), can also improve cycling performance of a-Fe 2 O 3 at a low current density of 100 mA g À1 .…”

The Preparation of Polyhedral -Fe2O3 Nanoparticles and their Sensing Properties

“…As the most stable iron oxide under ambient conditions, hematite(α-Fe 2 O 3 ) were used in the field of pigments [1], catalysts [2], magnetic recording media [3], water splitting [4], anticorrosive agents and gas sensors [5], owning to its low cost and environmental friendliness. Many efforts were devoted to preparing α-Fe 2 O 3 nanocrystals with different geometries and exposed surfaces owing to their shape-related properties [6,7].…”