Characterization of the ferritin iron core and the phosphate-doped ferrihydrite

High resolution transmission electron microscope (HRTEM, FEI Tecnai G2 F30, USA) with the selected area electron diffraction (SAED) was used to characterize the morphology and crystal lattice structure of the ferritin iron core and the phosphate-doped ferrihydrites. X-ray photoelectron spectroscopy (XPS, Thermo escalab 250Xi, monochromatic AlKα radiation accelerating voltage of 14.8 kV, power of 150 W, USA) was applied to characterize the element constitution and valence state. FTIR spectrum (Nicolet IS10, USA) was used to determine the specific functional group by scanning in the range of 400−4000 cm^-1 in the step of 4 cm^-1. X-ray powder diffractometer (XRD, Brucker D8 advance, Germany) was used to characterize the crystal structure of the ferritins and phosphate-dope ferrihydrite with the Cu (Kα) radiation in the range of 10−90° with the step of 4° min^-1.