Infrared study of surface phonon modes in α-Fe2O3microcrystals

A low-cost solvent-free method to synthesize α-Fe2O3 nanoparticles with applications to degrade methyl orange in photo-fenton system

Hematite nanoparticles (α-Fe₂O₃ NPs) were successfully synthesized by a low-cost solvent-free reaction using Ferrous sulfate waste (FeSO₄·7H₂O) and pyrite (FeS₂) as raw materials and employed for the decolorization of Methyl Orange by the photo-Fenton system. The properties of α-Fe₂O₃ NPs before and after photo-Fenton reaction were characterized by X-ray powder diffraction (XRD), Field emission scanning electron microscopy (FESEM), Fourier transform infrared (FT-IR) spectrum and X-ray photoelectron spectroscopy (XPS), and the optical properties of α-Fe₂O₃ NPs were analyzed by UV-vis diffuse reflectance spectra (UV-vis DRS) and Photoluminescence (PL) spectra. The analytic results showed that the as-formed samples having an average diameter of ~50 nm exhibit pure phase hematite with sphere structure. Besides, little differences were found by comparing the characterization data of the particles before and after the photo-Fenton reaction, indicating that the photo-Fenton reaction was carried out in solution rather than on the surface of α-Fe₂O₃ NPs. A 2⁴ central composite design (CCD) coupled with response surface methodology (RSM) was applied to evaluate and optimize the important variables. A significant quadratic model (P-value<0.0001, R² = 0.9664) was derived using an analysis of variance (ANOVA), which was adequate to perform the process variables optimization. The optimal process conditions were performed to be 395 nm of the light wavelength, pH 3.0, 5 mmol/L H₂O₂ and 1 g/L α-Fe₂O₃, and the decolorization efficiency of methyl orange was 99.55% at 4 min.

Hematite nanoparticle clusters with remarkably high magnetization synthesized from water-treatment waste by one-step “sharp high-temperature dehydration”

Hematite (α-Fe₂O₃) nanoparticle clusters with an exceptionally high magnetization of 51 emu g⁻¹ were synthesized for the first time. This material was prepared from water-treatment waste by a new “sharp high-temperature dehydration” process.

Understanding of the finite size effects on lattice vibrations and electronic transitions of nano alpha-Fe2O3

Alpha-Fe(2)O(3) nanocrystals with controlled diameters ranging from 10 to 63 nm were successfully prepared. The finite size effects in alpha-Fe(2)O(3) nanocrystals were probed by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, UV-visible spectrum, and magnetization measurements. With a size reduction, alpha-Fe(2)O(3) nanocrystals showed a lattice expansion and an enlarged axial ratio of c/a that is in apparent contradiction to the previous conjecture of high lattice symmetry for alpha-Fe(2)O(3) nanocrystals at small sizes. The surface terminations of alpha-Fe(2)O(3) nanocrystals were found to be highly hydrated with a size dependence that surprisingly follows the surface hydration chemistry of anatase TiO2 nanocrystals reported recently by us. The lattice vibrations, electronic transitions, and magnetic properties of alpha-Fe(2)O(3) nanocrystals were significantly modified by surface hydration and lattice expansion. The finite size effects that occurred in alpha-Fe(2)O(3) nanocrystals at small sizes were first found to give a red shift in frequencies of perpendicular mode at 540 cm(-1), a blue shift in the electronic transition of double exciton process in visible region, and a significant decrease in the coercive force.