An Fe−Ce bimetal adsorbent was investigated with X-ray powder diffraction (XRD), transmission electron micrograph (TEM), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS) methods for a better understanding of the effect of surface properties on arsenate (As(V)) adsorption. In the adsorption test, the bimetal oxide adsorbent showed a significantly higher As(V) adsorption capacity than the referenced Ce and Fe oxides (CeO2 and Fe3O4) prepared by the same procedure and some other arsenate adsorbents reported recently. XRD measurement of the adsorbent demonstrated that the phase of magnetite (Fe3O4) disappears gradually with the increasing dosage of Ce4+ ions until reaching a molar ratio of Ce4+ to Fe3+ and Fe2+ of 0.08:0.2:0.1 (Fe−Ce08 refers to the adsorbent prepared at this ratio), and the phase of CeO2 begins to appear following a further increase of the Ce dose. Combined with the results of TEM observation, it was assumed that a solid solution of Fe−Ce is formed follow...

Arsenate adsorption on an Fe-Ce bimetal oxide adsorbent: Role of surface properties

The preparation of magnetite, goethite, hematite and maghemite of pigment quality from mill scale iron waste

The long term growth of the protective rust layer formed on weathering steel by atmospheric corrosion during a quarter of a century

Using Fourier Transform InfraRed (FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), and Transmission Electron Microscopy (TEM), we characterize the structure and/or morphology of hematite (α-Fe2O3) particles with sizes of 7, 18, 39 and 120 nm. It is found that these nanoparticles possess maghemite (γ-Fe2O3)-like defects in the near surface regions, to which a vibrational mode at 690 cm−1, active both in FTIR and Raman spectra, is assigned. The fraction of the maghemite-like defects and the net lattice disorder are inversely related to the particle size. However, the effect is opposite for nanoparticles grown by sintering of smaller hematite precursors under conditions when the formation of a uniform hematite-like structure throughout the aggregate is restricted by kinetic issues. This means that not only particle size but also the growth kinetics determines the structure of the nanoparticles. The observed structural changes are interpreted as size-induced α-Fe2O3
				↔
				γ-Fe2O3 phase transitions. We develop a general model that considers spinel defects and absorbed/adsorbed species (in our case, hydroxyls) as dominant controls on structural changes with particle size in hematite nanoparticles, including solid-state phase transitions. These changes are represented by trajectories in a phase diagram built in three phase coordinates—concentrations of spinel defects, absorbed impurities, and adsorbed species. The critical size for the onset of the α
				→
				γ phase transition depends on the particle environment, and for the dry particles used in this study is about 40 nm. The model supports the existence of intermediate phases (protohematite and hydrohematite) during dehydration of goethite. We also demonstrate that the hematite structure is significantly less defective when the nanoparticles are immersed in water or KBr matrix, which is explained by the effects of the electrochemical double layer and increased rigidity of the particle environment. Finally, we revise the problem of applicability of IR spectroscopy to the lattice vibrations of hematite nanoparticles, demonstrating that structural comparison of different samples is much more reliable if it is based on the Eu band at about 460 cm−1 and the spinel band at 690 cm−1, instead of the A2u/Eu band at about 550 cm−1 used in previous work. The new methodology is applied to analysis of the reported IR spectra of Martian hematite.

Size-dependent structural transformations of hematite nanoparticles. 1. Phase transition.

Composition and protective ability of rust layer formed on weathering steel exposed to various environments

α-, γ-, δ- und amorphes FeOOH wurden als synthetische Pasten auf die Stahlsubstrate aufgegetragen.

The Electrochemical Reduction of Rust Films on Weathering Steel Surfaces

Characterization of the passive film formed on weathering steels

Infrared and Raman spectroscopy were used to study the oxidation of Fe3O4 on surfaces of weathering steel, carbon steel, and pure iron. Two sets of samples were polished and coated with an Fe3O4 paste. One set was moistened daily with distilled water and allowed to freely dry in air. The second set was treated in a similar manner except that every other day, a 0.1M Na2SO4 solution was used in place of the distilled water solution. In the set of samples treated only with distilled water, Fe3O4 was oxidized to γ-FeOOH on both the weathering and carbon steel surface, but oxidation of Fe3O4 was not observed on the pure iron surface. On all of the samples treated with 0.1M Na2SO4, Fe3O4 was oxidized initially to γ-FeOOH which converted to α-FeOOH after several weeks. The initial oxidation of Fe3O4 is proposed to occur by a reaction with H2O2 produced from the reduction of O2.

Joseph T. Keiser

Papers

The Electrochemical Reduction of Rust Films on Weathering Steel Surfaces

Characterization of the passive film formed on weathering steels

The Oxidation of Fe3O4 on Iron and Steel Surfaces

The electrochemical reduction of rust films on weathering steel surfaces