José Domingos Fabris

Activated carbon / iron oxide magnetic composites for the adsorption of contaminants in water

Abstract In this work the adsorption features of activated carbon and the magnetic properties of iron oxides were combined in a composite to produce magnetic adsorbents. These magnetic particles can be used as adsorbent for a wide range of contaminants in water and can subsequently be removed from the medium by a simple magnetic procedure. Activated carbon/iron oxide magnetic composites were prepared with weight ratios of 2:1, 1.5:1 and 1:1 and characterized by powder XRD, TG, magnetization measurements, chemical analyses, TPR, N2 adsorption–desorption isotherms, Mossbauer spectroscopy and SEM. The results suggest that the main magnetic phase present is maghemite (γ-Fe2O3) with small amounts of magnetite (Fe3O4). Magnetization enhancement can be produced by treatment with H2 at 600 °C to reduce maghemite to magnetite. N2 adsorption measurements showed that the presence of iron oxides did not significantly affect the surface area or the pore structure of the activated carbon. The adsorption isotherms of volatile organic compounds such as chloroform, phenol, chlorobenzene and drimaren red dye from aqueous solution onto the composites also showed that the presence of iron oxide did not affect the adsorption capacity of the activated carbon.

Clay–iron oxide magnetic composites for the adsorption of contaminants in water

Abstract In this work, the adsorption features of clays with the magnetic properties of iron oxides have been combined in a composite to produce a magnetic adsorbent. These magnetic composites can be used as adsorbent for contaminants in water and can be subsequently removed from the medium by a simple magnetic process. The bentonite–iron oxide magnetic composites have been prepared with weight ratios of 2:1, 1.5:1, and 1:1 and characterized by powder X-ray diffraction (XRD), thermogravimetric analysis (TG), magnetization measurements, chemical analyses, temperature-programmed reduction (TPR), N 2 adsorption–desorption isotherms, Mossbauer spectroscopy, and scanning electron microscopy (SEM). The results suggest that the main magnetic phase present is maghemite (γ-Fe 2 O 3 ). A magnetization enhancement can be produced by treatment with H 2 at 600 °C to reduce maghemite to magnetite. Nitrogen adsorption isotherms showed that the surface area and microporosity increased from 7 m 2 g −1 ( V micropores =0.003 cm 3 g −1 ) for the pure bentonite to 55 m 2 g −1 ( V micropores =0.009 cm 3 g −1 ) for the composite clay/iron oxide (2:1). The adsorption isotherms of metal ions Ni 2+ , Cu 2+ , Cd 2+ , and Zn 2+ from aqueous solution onto the composites also showed that the presence of iron oxide produced an increase on the adsorption capacity of the bentonite.

Synthesis and characterization of magnetic nanoparticles coated with silica through a sol-gel approach

This paper investigates the influence of reaction medium pH on silica-coating of magnetite nanoparticles. Magnetite nanoparticles were prepared by means of a reduction-precipitation method using ferric chloride as a starting material, which was partially reduced to ferrous salts by Na2SO3 before alkalinizing with ammonia. The particles were coated by sol-gel method with either ammonia or HCl aqueous solutions for either base- or acid-catalyzed hydrolysis, respectively. Powder X-ray diffraction, Fourier-transform infrared, and Zeta Potential were used for the characterization of oxides and of the coated magnetic nanoparticles. The observed difference of pHIEP in KCl solution for pure silica (2.0), magnetite (5.0), and silica-coated magnetite (2.3) samples confirms that the coating process was effective since the charge surface properties of coated magnetic nanoparticles are close to that of pure silica, even though the Fourier-transform infrared spectra did not evidence the formation of Fe-O-Si bonds.

Comparisons of structural iron reduction in smectites by bacteria and dithionite: II. A variable-temperature Mössbauer spectroscopic study of Garfield nontronite

The reduction of structural Fe in smectite may be mediated either abiotically by reaction with chemical reducing agents or biotically by reaction with various bacterial species. The effects of abiotic reduction on clay surface chemistry are much better known than the effects of biotic reduction, and differences between them are still in need of investigation. The purpose of the present study was to compare the effects of dithionite (abiotic) and bacteria (biotic) reduction of structural Fe in nontronite on the clay structure as observed by variable-temperature Mössbauer spectroscopy. Biotic reduction was accomplished by incubating Na-saturated Garfield nontronite (sample API 33a) with Shewanella oneidensis strain MR-1 (FeII/total Fe achieved was ~17 %). Partial abiotic reduction (FeII/total Fe ~23 %) was achieved using pH-buffered sodium dithionite. The nontronite was also reduced abiotically to FeII/total Fe ~96 %. Parallel samples were reoxidized by bubbling O2 gas through the reduced suspensions at room temperature prior to Mössbauer analysis at 77 and 4 K. At 77 K, the reduction treatments all gave spectra composed of doublets for structural FeII and FeIII in the nontronite. The spectra for reoxidized samples were largely restored to that of the unaltered sample, except for the sample reduced to 96 %. At 4 K, the spectrum for the 96 % reduced sample was highly complex and clearly reflected magnetic order in the sample. When partially reduced, the spectrum also exhibited magnetic order, but the features were completely different depending on whether reduced biotically or abiotically. The biotically reduced sample appeared to contain distinctly separate domains of FeII and FeIII within the structure, whereas partial abiotic reduction produced a spectrum representative of FeII–FeIII pairs as the dominant domain type. The 4 K spectra of the partially reduced, fully reoxidized samples were virtually the same as at 77 K, whereas reoxidation of the 96 % reduced sample produced a spectrum consisting of a magnetically ordered sextet with a minor contribution from a FeII doublet, indicating significant structural alterations compared to the unaltered sample.

Nanostructured δ-FeOOH: a novel photocatalyst for water splitting

We report on the first use of nanostructured δ-FeOOH as a promising photocatalyst for hydrogen production. The high surface area, interparticle mesoporosity, small particle size and band gap energy in the visible region make nanostructured δ-FeOOH a suitable candidate for use as a photocatalyst.

Use of activated carbon as a reactive support to produce highly active-regenerable Fe-based reduction system for environmental remediation

Composites based on iron supported on high surface area activated carbon were prepared and characterized with (57)Fe Mössbauer spectroscopy, X-ray diffraction, saturation magnetization measurements and temperature-programmed reduction. Upon thermal treatment, the supported iron oxides react with carbon to yield reduced chemical species, i.e. Fe(3)O(4) and Fe(0). This so produced composite was found to be highly efficient in two environmental applications: (i) degradation of textile dye and (ii) reduction of Cr(VI) in aqueous medium. Sequential reuses evidenced a progressive chemical deactivation of the composites due to a corresponding oxidation of the reactive species. Even after being virtually deactivated, the initial chemical reducing ability of the composites can be regenerated by heating at 800 degrees C under N(2) atmosphere, and then reused for several consecutive times.

IRON OXIDES IN A SOIL DEVELOPED FROM BASALT

A dusky red Oxisol forming on a tholeiitic basalt is found to contain varying proportion of aluminous hematite (Hm) and titanoaluminous maghemite (Mh) in the different size fractions. Maghemite is the main iron oxide in the sand and silt fractions whereas Hm is dominant in the clay fraction, together with gibbsite (Gb), kaolinite (Ka), rutile (Rt) (and probably anatase, An) and Mh. Maghemite is also the major oxide mineral in the magnetic separates of soil fractions (sand, about 65% of the relative Mössbauer spectral area; silt, 60%). Hematite (sand, 30%; silt, 15%) and ilmenite (Im) (sand, 5%; silt, 16%) are also significantly present in the magnetic extract. Accessory minerals are Rt and An. No magnetite (Mt) was detected in any soil fraction. Sand- and silt-size Mh have similar nature (a0= 0.8319 ± 0.0005 nm; about 8 mol% of Al substitution; saturation magnetization of 49 J T−1 kg−1), and certainly a common origin. Lattice parameters of clay-Mh are more difficult to deduce, as magnetic separation was ineffective in removing nonmagnetic phases. Al content in Hm varies from 14 mol% (clay and silt) to 20 mol% (sand). The proposed cation distribution on the spinel sites of the sand-size Mh is:

Magnetic soils from mafic lithodomains in Brazil

\rm{[Fe_{0.92}Al_{0.08}] {Fe_{1.43}Ti_{0.18}\square_{0.39}}O_4}