Preparation of nano Fe 3 O 4 pigment using CO 3 2− /HCO 3 − as precipitant and DFT study on the formation process of its intermediate product FeOOH

The nano Fe3O4 pigment was prepared with a precipitation method using the carbonate/bicarbonate as precipitant. The chemical structure, crystal phase and morphology of prepared pigment samples were determined by fourier transform infrared spectroscopy (FT-IR), X-ray diffraction spectrometer (XRD), transmission electron microscope (TEM), high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED), and its color performance was tested. The results showed that the prepared pigment sample showed high purity and excellent crystallinity of bulk Fe3O4, and better black property (L* = 35.51) than the commercially available standard pigment sample. The characterization results of pigment samples obtained under different preparation parameters showed that the precipitant reaction temperature and reaction time showed obvious effect on the morphology, crystallization degree and color performance of prepared nano Fe3O4 pigment. In addition, it was found that the FeOOH was the intermediate product. The density functional theory (DFT) calculation results revealed that the generation of FeOOH was realized through a series of reaction steps including dehydrogenative oxidation, dehydration, and dimerization, in which the FeCO3 instead of the Fe(OH)2 was served as the initial phase of Fe(II) compounds.