- Morphology analysis of porous Fe2O3 nanotubes
Figure 1 shows the SEM images of electrospinning nanofibers and porous Fe2O3 nanotubes. From Fig. 1, we can see that the nanofibers prepared by electrospinning are about 520 nm in diameter and have a smooth surface without any holes and secondary structures [Fig. 1(a) and Fig. 1(b)]. After high temperature calcination, although the obtained material maintains a one-dimensional structure, a large number of holes and a hollow porous tubular structure appear on the surface, and its diameter is reduced to 400 nm [Figure 1(c) and Figure 1(d)]. Indeed, the decomposition of polyvinylpyrrolidone, organic salts, and the formation of Fe2O3 during calcination resulted in a reduction in diameter and the formation of porous tubular structures.
Transmission electron microscopy was used to further observe the morphology of the porous Fe2O3 nanotubes. Figure 2 clearly confirms the existence of porous Fe2O3 nanotubes, which is consistent with the SEM observations. High-resolution transmission electron microscopy also confirmed that the porous Fe2O3 nanotubes are composed of interconnected nanoparticles. And by analyzing its high-resolution transmission electron microscope, it can be confirmed that the lattice spacing of 0.37 nm is the lattice spacing of Fe2O3 (012) plane. The above results can be fully confirmed by many
- Structural analysis of porous Fe2O3 nanotubes
Figure 3 is the X-ray diffraction (XRD) spectrum of the prepared porous Fe2O3 nanotubes, and we give the crystal plane parameters of typical crystal plane peaks. It can be seen from Figure 4-3 that the diffraction angles 2θ of 24.15°, 33.3°, 35.8°, 40.6°, 49.4°, 54.1°, 57.4°, 62.3°, 63.9° and 71.9° belong to (012), ( Diffraction peaks of 104), (110), (113), (024), (116), (122), (214), (030) and (220) crystal planes. The diffraction peak of this sample corresponds to rhombohedral hematite (JCPDS No. 33-0664). It can be seen that this method can prepare hematite (Fe2O3). It can also be seen from FIG. 3 that there is no impurity phase, and the diffraction peak intensity of the prepared porous Fe2O3 nanotubes is higher, indicating that the prepared porous Fe2O3 nanotubes have higher crystallinity.
Thermogravimetric analysis was used to observe the relationship between the weight of iron acetylacetonate/polyvinylpyrrolidone nanofibers as a function of calcination temperature. Clearly, the weight loss of the electrospun fibrous membrane was caused by the decomposition of iron acetylacetonate and polyvinylpyrrolidone throughout the temperature increase. The weight loss process mainly includes the following 3 stages: ①20~200℃; the weight loss in this stage can be attributed to the volatilization of solvents such as water and N,N-dimethylformamide; ②200~400℃: This is due to the acetyl Caused by the decomposition of ferric acetone and polyvinylpyrrolidone [25]; ③400~500 °C: In this stage, the residues of polymer decomposition are mainly further oxidized, which is consistent with the results reported in many literatures [26]. When the temperature exceeds 500 °C, the weight loss is caused by the change of the crystal structure of α-Fe2O3, so 500 °C is selected as the calcination temperature for the preparation of porous Fe2O3 nanotubes in this experiment.
Next, we used XPS to further characterize the purity, composition, and fine structure of the samples. It can be seen from Figure 4(a) that there are typical Fe2p and O 1s peaks in the XPS spectrum, which can confirm that the samples contain iron and oxygen elements. In Fig. 4(b), Fe2p3/2 and Fe2p1/2 peaks of iron appear at 711.3eV and 724.7eV, while at 719eV are typical characteristic peaks of Fe3+, thus confirming the formation of α-Fe2O3. While the asymmetric O1s spectrum in Fig. 4(c) is split into two peaks at 529.7 eV and 531.0 eV, which can be attributed to lattice oxygen OFe-O and hydroxyl OH-O [27]. To further confirm the specific surface area and pore size distribution of the samples, we tested them using the N.2-adsorption-desorption technique. It can be seen from the N2 isotherm adsorption and desorption curve in Figure 4(d) that the specific surface area of the prepared sample is 23 m2/g. It can be seen from the BJH pore size distribution curve in the inset that the pore size distribution is wide and has obvious mesoporous structure.
- Formation mechanism of Fe2O3 nanomaterials with different morphologies
In order to illustrate the formation mechanism of Fe2O3 nanomaterials with different morphologies in detail, we investigated the morphologies of a series of samples obtained by calcining a series of precursor fibers containing iron acetylacetonate of different quality. Figure 5 reveals the morphology transformation process from nanostrips to nanotubes. Significantly, electrospun nanofibers
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