Figure 3 TEM images and SAED patterns of α-Fe 2 O 3 hexagonal plates (a, b), α-Fe 2 O 3 hexagonal bipyramid (c, d), and Fe 3 O 4 polyhedral particles (e, f). To further understand the formation process of Fe3O4, the reaction
systems with the addition of both KOH and EDA were hydrothermally synthesized at 200°C for different reaction times, as shown in Figure 4. Figure 4a shows that, after 2 h of growth, the main phase of the particles is α-Fe2O3 hexagonal plates. The edge of the hexagonal Semaxanib cost plate is not as straight as that obtained for the reaction system with KOH only. As the reaction time increased to 5 h, as shown in Figure 4b, small octahedron particles were observed and the original hexagonal plate started to dissolve and no longer maintained the hexagonal shape. As the reaction time continued to increase to 7 h, more polyhedron particles were observed with larger sizes and only a small amount of plate-like
particles still existed, as shown in Figure 4c. At the reaction time of 9 h, the observed particles are mainly polyhedron ones, as shown in Figure 4d. The first observation in this sequence of experiment is that KOH can rapidly transform iron hydroxides to hematite. The second observed phenomenon is that the α-Fe2O3 hexagonal plates were dissolved to become irregular plates during the transformation process. Figure 4 Mixture of α-Fe 2 O 3 and Fe 3 O 4 particles precipitated in the hydrothermal system at 200 °C at different times. (a) 2 h, (b) 5 h, (c) 7 h, and (d) 9 h. The result implied that phase transformation CB-839 evolved in four steps: (1) the reaction systems rapidly transformed Fe(OH)3 or FeOOH to α-Fe2O3 hexagonal plates under the hydrothermal conditions, (2) the α-Fe2O3 hexagonal plates dissolved gradually, (3) the reduction process causes valence transition of Fe3+ to Fe2+, and (4) the Fe3O4 particles started to nucleate and then finally grew to form polyhedral particles. To further understand HSP90 the role of NO3 – ions on the phase
transition process, the precursor of FeNO3 was substituted by FeCl3 with the same hydrothermal conditions. Two cases were investigated, one with the addition of KOH only and the other with the addition of both KOH and EDA under the same hydrothermal condition of 200°C for 9 h. Figure 5a shows that the α-Fe2O3 hexagonal plates were obtained when the reaction system consists of FeCl3 and KOH, while the phase transformation from α-Fe2O3 hexagonal plates to Fe3O4 polyhedral particles still occurred when the reaction system consists of FeCl3, KOH, and EDA, as shown in Figure 5b. The shape of the polyhedral particles is more irregular in this case. The XRD patterns, shown in Figure 4c, confirmed the related phases. Notice that the α-Fe2O3 plates were not completely reduced to Fe3O4 particles. Thus, NO3 – ions are not directly involved in the reduction process of Fe3+ to Fe2+.