FIGURE 1 Schematic diagram of the synthesis of Fe3O4@C and adjustment of the surface structure by controlling relative distance to the magnet. The inserted image shows light reflection inside the spine arrays.
2. Results and Discussion
2.1. Characterization of carbon-coated nanoparticles
The carbon-coated nanoparticles were synthesized by a typical hydrothermal method. After coating with a carbon layer, the carbon-coated nanoparticles remain granular and have a certain dispersion (Figure S2a-b). In the experiment, the thickness of carbon layer was changed by adjusting the amount of glucose as carbon source. As TEM images shown in Figure 2a-c, Fe3O4@C had a carbon layer at the thickness of ~15 nm. While, as 2 g of glucose was used in preparation, the thickness of carbon layer of Fe3O4@tC was up to ~28 nm. Following the particle size distribution in Figure 2d, the major particle sizes of Fe3O4, Fe3O4@C and Fe3O4@tC were about 666 nm, 691 nm and 715 nm, respectively. In comparison to the pristine magnetic nanoparticle, Fe3O4@C and Fe3O4@tC revealed increases in diameter of 25 nm and 49 nm, which were generally consistent with the results in TEM images.