Abstract
Hollow or porous hematite (α-Fe2O3) nanoarchitectures have emerged as promising crystals in the advanced materials research. In this contribution, hierarchical mesoporous α-Fe2O3 nanoarchitectures with a pod-like shape were synthesized via a room-temperature coprecipitation of FeCl3 and NaOH solutions, followed by a mild hydrothermal treatment (120°C to 210°C, 12.0 h). A formation mechanism based on the hydrothermal evolution was proposed. β-FeOOH fibrils were assembled by the reaction-limited aggregation first, subsequent and in situ conversion led to compact pod-like α-Fe2O3 nanoarchitectures, and finally high-temperature, long-time hydrothermal treatment caused loose pod-like α-Fe2O3 nanoarchitectures via the Ostwald ripening. The as-synthesized α-Fe2O3 nanoarchitectures exhibit good absorbance within visible regions and also exhibit an improved performance for Li-ion storage with good rate performance, which can be attributed to the porous nature of Fe2O3 nanoarchitectures. This provides a facile, environmentally benign, and low-cost synthesis strategy for α-Fe2O3 crystal growth, indicating the as-prepared α-Fe2O3 nanoarchitectures as potential advanced functional materials for energy storage, gas sensors, photoelectrochemical water splitting, and water treatment.
Highlights
Three-dimensional hierarchical architectures, or nanoarchitectures, assembled by one-dimensional (1D) nanostructures have attracted extraordinary attention and intensive interests owing to their unique structures and fantastic properties different from those of the monomorph structures [1,2,3,4,5]
We developed a hydrothermal synthesis of the porous hematite with a pod-like morphology or short-aspect-ratio ellipsoidal shape in the presence of H3BO3 [44]
Quasi-spherical hematite NPs with a diameter of 30 to 150 nm were obtained when the molar ratio of FeCl3/H3BO3/NaOH was 2:0:6 (Figure 1b,b1), similar to the so-called α-Fe2O3 nanopolyhedra synthesized in the ammonia-water system at 180°C for 8.0 h [23]
Summary
Three-dimensional hierarchical architectures, or nanoarchitectures, assembled by one-dimensional (1D) nanostructures have attracted extraordinary attention and intensive interests owing to their unique structures and fantastic properties different from those of the monomorph structures [1,2,3,4,5]. In contrast to graphite electrodes, the lithium storage within iron oxides is mainly achieved through the reversible conversion reaction between lithium ions and metal nanocrystals dispersed in a Li2O matrix [24]. Such a process usually causes drastic volume changes (>200%) and severe destruction of the electrode upon electrochemical cycling, especially at a high rate [24]. The mesoporous α-Fe2O3 nanoarchitectures may afford several advantages for LIB application, such as the extended contact area between the active material and the electrolyte as well as the short lithium diffusion length resulting from the thin shell and the hollow space in the central part that buffers the volume expansion during cycling [22,27,28]
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