α-Fe2O3 Composites Research Articles

Sorption-reduction removal of Cr(VI) from aqueous solution by the porous biomorph–genetic composite of α-Fe2O3/Fe3O4/C with eucalyptus wood hierarchical microstructure

A porous biomorph–genetic composite of α-Fe2O3/Fe3O4/C (PBGC-Fe/C) with eucalyptus wood hierarchical microstructure was prepared and characterized. The result indicated that the PBGC-Fe/C material retained the hierarchical porous structure of eucalyptus wood with three different types of pores (widths 70–120, 4.1–6.4 and 0.1–1.3 μm) originating from vessels, fibres, and pits of the wood, respectively. Batch experiments were conducted to evaluate the effects of different parameters on Cr(VI) adsorption systematically. With increasing initial concentration from 10 to 150 mg/L, the amounts of Cr(VI) adsorbed on the pulverized PBGC-Fe/C adsorbent (<0.149 mm) increased from 1.00 to 4.01 mg/g at 25°C, from 1.00 to 4.22 mg/g at 35°C, and from 1.00 to 4.52 mg/g at 45°C. At the initial concentrations of 2, 10, and 50 mg/L, the adsorption capacities for the unpulverized PBGC-Fe/C adsorbent (##xgt;0.841 mm) were determined to be 0.20, 0.92, and 2.96 mg/g, respectively, which exhibited a similar average value to those of fine particles or nanoparticles of iron oxides. The adsorption followed Freundlich as well as Langmuir isotherms and could well be described by the pseudo-second-order kinetic equation. X-ray photoelectron spectroscopy studies showed that the main mechanism of Cr(VI) removal was a sorption-redox reaction between Cr(VI) and the PBGC-Fe/C adsorbent.

Fabrication, characterization, and photocatalytic property of α-Fe2O3/graphene oxide composite

Spindle-shaped microstructure of α-Fe2O3 was successfully synthesized by a simple hydrothermal method. The α-Fe2O3/graphene oxide (GO) composites was prepared using a modified Hummers’ strategy. The properties of the samples were systematically investigated by X-ray powder diffraction (XRD), UV–Vis diffuse reflectance spectrophotometer, transmission electron microscope, atomic force microscope, X-ray photoelectron spectroscopy, and Raman spectroscopy (Raman) techniques. GO nanosheets act as supporting materials for anchoring the α-Fe2O3 particles. The average crystallite sizes of the α-Fe2O3 and α-Fe2O3/GO samples are ca. 27 and 24 nm, respectively. The possible growth of α-Fe2O3 onto GO layers led to a higher absorbance capacity for visible light by α-Fe2O3/GO than α-Fe2O3 composite. The photocatalytic degradation of toluene over the α-Fe2O3 and α-Fe2O3/GO samples under xenon-lamp irradiation was comparatively studied by in situ FTIR technique. The results indicate that the α-Fe2O3/GO sample synthesized exhibited a higher capacity for the degradation of toluene. The composite of α-Fe2O3/GO could be promisingly applied in photo-driven air purification.

Kinetics and Thermodynamics of Sorption for As(V) on the Porous Biomorph-Genetic Composite of α-Fe2O3/Fe3O4/C with Eucalyptus Wood Hierarchical Microstructure

A novel porous biomorph-genetic composite of α-Fe2O3/Fe3O4/C (PBGC-Fe/C) with eucalyptus wood template was prepared, characterized and tested for its sorption capacity of As(V) from aqueous solution. The result indicated that the PBGC-Fe/C material retained the hierarchical porous structure of eucalyptus wood with three different types of pores (widths 70∼120, 4.1∼6.4 and 0.1∼1.3 μm) originating from vessels, fibres and pits of the wood, respectively. Its surface area was measured to be 59.2 m2/g. With increasing initial As(V) concentration from 5 to 100 mg/L, the amounts of As(V) sorbed on the pulverized PBGC-Fe/C sorbent ( 3 mm) were determined to be 0.50, 0.99 and 2.49 mg/g, respectively, which exhibited a similar average value to those of fine particles or nanoparticles of iron oxides. The sorption could well be described by the pseudo-second-order kinetic equation. The equilibrium data were found to follow Freundlich as well as Langmuir isotherms.

Role of Oxidation State of Vanadium in Vanadium Oxide-Hematite Nanoparticles

ABSTRACTSingle phase, a FeVO4 triclinic crystalline structure was successfully synthesized by annealing the mechanochemically milled xV2O5·(1-x)α-Fe2O3 composites (x = 0.5) at 550 °C for 1 h. X-ray powder diffraction (XRD) and Mössbauer spectroscopy were combined for a detailed study of the assisting role of the mechanochemical milling process. Mechanochemical milling homogeneously mixed the starting materials of α-Fe2O3 and V2O5 and substantially decreased their average grain sizes. The partially V5+-substituted α-Fe2O3 phase and Fe3+-substituted V2O5 could be the important intermediate phases in the production of FeVO4 single phase. In addition, xV2O3·(1-x)α-Fe2O3 (x = 0.1, 0.3, 0.5, and 0.7) solid solutions were successfully synthesized by mechanochemical activation of V2O3 and α-Fe2O3 mixtures. Complete solid solutions exist after 12 h ball-milling time for all studied x values. The synthesized xV2O3·(1-x)α-Fe2O3 solid solutions with x = 0.5 and 0.7 were mainly paramagnetic at room temperature. The study demonstrates that the transformation pathway is related to the valence state of the metallic specie of the oxide used in connection with hematite.

Erratum to: Impedance spectroscopy study on the ionic conductivity processes of the novel LiFeVO4 phase

In the paper of Ref. [1], we presented results of studies detailing the electrical properties of a vanadate phase then believed to be a novel compound with the chemical formula LiFeVO4. Since the time of that publication, we have endeavored to probe further into the properties of this material to elucidate the relationships between its structural and electrical properties. This erratum presents recent results that put in doubt the nature of the phase produced and reported in [1]. Our finding is that the primary phase could not be LiFeVO4 as first believed, but instead a LiVO3 and α-Fe2O3 composite. At the time our work was submitted to Ionics there were only two reports claiming the existence of a novel compound with the chemical formula LiFeVO4 [2, 3]. At that time we were studying the conductivity processes in a whole series of LiMVO4 (M=Ni, Co, Zn, Mn, Mg) and therefore we found it intriguing to further investigate the conductivity properties of a novel vanadate. As we mention in [1] “Impedance spectroscopy study of the compound LiFeVO4 has been performed in [11, Ref. 2 of this erratum] and the equivalent circuits of the compound have been given at 25, 50, 75, 100, 125 and 250°C. In that paper a study of the variation of impedance versus temperature at 50, 100, 125 and 250°C is presented. In our present work an impedance spectroscopy study of the novel compound LiFeVO4 is presented based on a different methodology and perspective than that reported in [11].” Additionally we expanded the temperature range up to 500°C. In Ref. [2] a detailed description of the reaction processes and of the characterization (though preliminary) of the reaction product were presented. In the case of the discovery of a new phase it is common that a provisional structural characterization is provided and in a follow-up work of the same or other authors the actual structural description is given. Based on that we repeated the reaction described in [2] and found that the XRD pattern of our product was identical to that given in [2] unfortunately disregarding the obvious fact that the latter is smoothed. However, we stated in [1] “The main diffraction peaks in Fig. 2 completely coincide with the XRD pattern given in Ref. [11] (in a 20–80° interval) and could be indexed according to that preliminary study in the orthorhombic system, see Fig. 2. In our pattern there are some small peaks which cannot be seen in the smoothed pattern provided in [11,13]. Nevertheless, there is not another source of information in literature for the XRD study of LiFeVO4”. It turns out that there was a simple reason for the existence of these unidentified peaks. Recently, we realized that the XRD pattern of our product can be also indexed considering a two phase system consisting of LiVO3 and α-Fe2O3 [4]. Therefore, we performed a Rietveld analysis on the same X-ray diffraction pattern which has been reported in [1]. Thus, that XRD pattern was treated as a mixture of two phases, α-Fe2O3 and LiVO3. For the latter the structure model described by Muller et al. [5] was The online version of the original article can be found at http://dx.doi. org/10.1007/s11581-010-0428-z.

Enhancement of photogenerated charges separation in α-Fe2O3 modified by Zn2SnO4

The composite of α-Fe2O3/Zn2SnO4 was synthesized via a sol–gel route. Photoelectric properties are investigated by surface photovoltage spectroscopy and electric field-induced surface photovoltage spectroscopy. The photovoltaic response for the composite with the molar ratio 4 : 1 of α-Fe2O3 to Zn2SnO4 without bias is similar to that for the pristine α-Fe2O3 under positive bias. The results show that the modification of Zn2SnO4 can significantly improve the surface photovoltaic response of α-Fe2O3. The enhanced photogenerated charges separation could be ascribed to the good contact and energy level matching between α-Fe2O3 and Zn2SnO4. The high electron mobility and low rate of electron–hole recombination in Zn2SnO4 are also responsible for the improved photoelectric properties of α-Fe2O3.

Mesoporous TiO2/α-Fe2O3: Bifunctional Composites for Effective Elimination of Arsenite Contamination through Simultaneous Photocatalytic Oxidation and Adsorption

Bifunctional mesoporous TiO2 (meso-TiO2)/α-Fe2O3 composites are successfully synthesized by impregnation of Fe3+ into meso-TiO2 followed by calcination at 300 °C. The composites are characterized by wide-angle X-ray powder diffraction, small-angle X-ray diffraction, and transmission electron microscopy. The “bifunctional” means that the composites possess synergy of the photocatalytic ability of meso-TiO2 for oxidation of As (III) to As (V) and the adsorption performance of α-Fe2O3 for As (V). Experimental results show that the meso-TiO2/α-Fe2O3 composites can oxidize higher toxic As (III) to lower toxic As (V) with high efficiency at various pH values in the photocatalysis reaction. At the same time, As (V) is effectively removed by adsorption onto the surface of composites. In addition, As (V) can be easily desorbed from the composites by heat treatment in alkali solution. After reusage for several times, the composites still present comparable catalysis and adsorption performance with that of first use, indicating the excellent stability of the bifunctional composites. The reasonable mechanism for the formation of meso-TiO2/α-Fe2O3 composites, the photocatalytic oxidation of As (III) to As (V) and simultaneous removal of As (V) are also presented in this paper. The bifunctional composites are expected to have significant applications in treating water contamination.

Hierarchically porous Fe2O3 and Fe2O3/SiO2 composites prepared by cypress tissue template with assistance of supercritical CO2

Hierarchically porous α-Fe2O3 and silica-based Fe2O3 composites (I &amp; II) ranging from nanopores to micrometer-sized pores have been prepared by a nanoscale casting process, using cypress wood tissue template in supercritical carbon dioxide (scCO2). These wood-templated Fe2O3 and its SiO2-based composites with special hierarchical but continuous pore size from 9 nm up to 20 μm, were prepared from scCO2’ hybrid solution with cosolvent and precursor(s). Different characterization techniques such as SEM, XRD, and N2 adsorption-desorption were used to investtig-ate the morphology and structure of Fe2O3 and its composites in different length scales. The Fe2O3 porous material showed a specific character-istic of being accumulated by Fe2O3 granules in the size range ca. 100–200 nm. The SiO2-based Fe2O3 composites exhibited a BET area of 99–104 m2/g, which was much higher than that of pure Fe2O3; this implies that the silica probably exists in the form of a gel skeleton.