FIGURE 2 TEM images (a-c), particle sizes distributions (d), Raman spectra (e) and XRD spectra (f) of Fe3O4, Fe3O4@C and Fe3O4@tC.
Raman spectra of as-prepared samples were investigated to analysis the carbon layer (Figure 2e). There were two typical D band and G band at 1350 and 1580 cm-1 respectively confirmed in both Fe3O4@C and Fe3O4@tC, which indicated the relatively low graphitization of the carbon layer.36 In XRD patterns, pristine nanoparticles showed the diffraction peaks at 30, 35, 43, 53, 57 and 63° corresponding to the (220), (311), (400), (422), (511) and (440) of Fe3O4 crystal. Fe3O4@C and Fe3O4@tC showed similar patterns without a noticeable change in these characteristic peaks, indicating no oxidation during the hydrothermal synthesis (Figure 2f).
2.2. Characterization of magnetic photothermal evaporator
The morphology assembled by the magnetic nanoparticles was controlled by the magnetic field. Therefore, the numerical simulation based on finite-element analysis was applied for the analysis of the magnetic field distribution (Figure 3 and Figure S4).