- Synthesis of Fe3O4/TiO2 secondary heterostructures
Figure 1 systematically demonstrates the preparation process of Fe3O4/TiO2 secondary heterostructures, mainly including electrospinning technology and hydrothermal method. Obviously, one-dimensional TiO2 nanofibers with smooth surface can be obtained by a simple and easy electrospinning technique, and then Fe3O4 nanoparticles can be grown on the surface of smooth one-dimensional TiO2 nanofibers by hydrothermal method. Similarly, different metal oxides can be grown on the surface of TiO2 nanofibers by changing the types of metal salts in the reactor. Although two synthetic methods are used in the whole synthesis process, the whole synthesis process does not require the introduction of other functional groups or the surface treatment of the substrate (TiO2 nanofibers) by covalent and non-covalent attachment, so that two different metals can be realized. Compounding of oxides. Therefore, the process is simple and easy.
- Morphology analysis of Fe3O4/TiO2 secondary heterostructures
Fig. 2(a) shows the scanning electron microscope picture of TiO2 nanofibers. It can be seen from Fig. 2(a) that the surface of TiO2 nanofibers is smooth without any secondary structure, and the diameter is about 220 nm. Then, after the TiO2 nanofibers were placed in a reaction kettle containing FeCl3•6H2O, the surface of the nanofibers changed significantly after the hydrothermal reaction. It can be seen from the SEM picture of the composite material [Fig. 2(b)] that some granular secondary structures have grown on its surface. Significantly, the diameter of the composite material has increased to about 250 nm. High-resolution transmission electron microscopy further demonstrated the formation of the composite [Fig. 2(c)].
To confirm the composition of the composite, we performed high-resolution tests on its different regions. By analyzing the junction of the heterostructure of the composite material, it can be found that there are two types of interplanar spacing [Fig. 2(d)], where the interplanar spacing of 0.35 nm corresponds to the 101 crystal plane of anatase TiO2, and the interplanar spacing If it is 0.254nm, it corresponds to the 311 crystal face of Fe3O4. This result confirms the existence of two oxides, TiO2 and Fe3O4, at the interface of the composite heterostructure. Then, by analyzing the particles on the surface of the composite material, only one type of interplanar spacing was found [Fig. 2(e)]. The interplanar spacing of 0.254 nm corresponds to the 311 crystal plane of Fe3O4, so it was confirmed that the particles on the surface were Fe3O4.
In order to further confirm that the composite is a core-shell structure with Fe3O4 coated on the surface of TiO2, we performed a linear scan on the composite. Figure 2(f) shows that Fe is mainly distributed in the outer part of the composite, while Ti is mainly distributed in the inner part of the composite. In conclusion, Fe3O4/TiO2 secondary heterostructures coated with Fe3O4 nanoparticles on the surface of TiO2 have been successfully prepared. Moreover, the number of Fe3O4 nanoparticles coated on the surface of TiO2 can be realized by changing the content of FeCl3•6H2O in the reaction precursor. As shown in Fig. 3, when the mass of FeCl3•6H2O in the reaction precursor drops to 0.05 g, the Fe3O4 nanoparticles on the surface of the obtained composite material are significantly reduced, so the morphology of Fe3O4/TiO2 secondary heterostructure is adjustable of.
- Structural analysis of Fe3O4/TiO2 secondary heterostructures
Figure 4(a) is the XRD of the as-prepared TiO2 nanofibers and Fe3O4/TiO2 secondary heterostructures
In the spectrum, we give the crystal plane parameters of typical crystal plane peaks. As can be seen in Fig. 4(a), all the diffraction peaks can be indexed as anatase TiO2 (JCPDS No. 21-1272) and cubic Fe3O4 (JCPDS No. 19-0629). Next, we used XPS to characterize the purity, composition, and fine structure of the samples. The presence of typical C 1s, O 1s, Ti 2p and Fe 2p peaks in Fig. 4(b) can confirm that the samples contain carbon, oxygen, titanium and cobalt elements. Looking closely at the inset of Fig. 4(b), we find that peaks of Fe 2p3/2 and Fe 2p1/2 appear at 711 eV and 724 eV. This is the typical XPS peak of Fe3O4, thus confirming the formation of Fe3O4.
So far, the formation of Fe3O4/TiO2 secondary heterostructure has been fully confirmed by various characterization methods. Next, for the proportion of Fe3O4 and TiO2 in the secondary heterostructure, we used inductively coupled plasma atomic emission spectrometry to test the content of iron in the composite species, and the result was 18.2% (mass fraction). However, the content of iron in the prepared secondary heterostructure of Fe3O4 particles coated with TiO2 is only 14.0% (mass fraction).