α-Fe2O3 versus β-Fe2O3: Controlling the Phase of the Transformation Product of ε-Fe2O3 in the Fe2O3/SiO2 System
Abstract
The influence of added sucrose on the phase composition of iron oxide nanoparticles was studied in the Fe2O3/SiO2 nanocomposites. The nanocomposites were prepared byimpregnation of mesoporous silica SBA-15 with iron nitrate containing various amounts of sucrose and their subsequent annealing at 1100 and 1200 oC.
The phase composition of the iron oxide nanoparticles in the prepared nanocomposites was analyzed by X-ray diffraction and 57Fe Mössbauer spectroscopy on polycrystalline samples. Profile analysis of the X-ray diffraction maxima was used to determine the apparent crystallite size of the different polymorphs.
The content of β-Fe2O3 in the samples increased with an increasing amount of sucrose, and no β-Fe2O3 was observed in the samples without sucrose. These samples contained only ε-Fe2O3 and hematite.
The apparent crystallite size was found to be similar for both hematite and β-Fe2O3. Therefore, sucrose was identified as the primary variable, which directs the ε-Fe2O3 transformation to either hematite or β-Fe2O3.
Our findings shift the way we understand the β-Fe2O3 formation from ε-Fe2O3 in the Fe2O3/SiO2 system from the size-directed to the starting materialdirected transformation.