Immobilized cells of Acidithiobacillus ferrooxidans in PVC strands and sultite removal in a pilot-scale bioreactor

The biooxidation of ferrous ion into ferric ion by Acidithiobacillus ferrooxidans can be potentially used for the removal of H2S from industrial gases. In this work, Fe3+ ions were obtained through the oxidation of Fe2+ using the LR strain of At. ferrooxidans immobilized in PVC stands in a pilot-scale bioreactor, while H2S was removed in an absorption tower equipped with Rasching rings. At. ferrooxidans LR strain cells were immobilized by inoculating the bacterium in a Fe2+-mineral medium and percolating it through the support. After complete Fe2+ oxidation, which took around 90 h, the reactor was washed several times with sulfuric acid (pH 1.7) before a new cycle was started. Four additional cycles using fresh Fe2+ mineral medium were then run. During these colonization cycles, the time required for complete iron oxidation decreased, dropping to about 60 h in the last cycle. The batch experiments in the H2S gas removal trials resulted in a gas removal rate of about 98-99% under the operational conditions employed. In the continuous experiments with the bioreactor coupled to the gas absorption column, a gas removal efficiency of almost 100% was reached after 500 min. Precipitate containing mainly sulfur formed during the experimental trial was identified by EDX. (c) 2005 Elsevier B.V. All rights reserved.

Influence of the iron source on the solar photo-Fenton degradation of different classes of organic compounds

In this work the influence of two different iron sources, Fe(NO3)(3) and complexed ferrioxalate (FeOx), on the degradation efficiency of 4-chlorophenol (4CP), malachite green, formaldehyde, dichloroacetic acid (DCA) and the commercial products of the herbicides diuron and tebuthiuron was studied. The oxidation of 4CP, DCA, diuron and tebuthiuron shows a strong dependence on the iron source. While the 4CP degradation is favored by the use of Fe(NO3)(3), the degradation of DCA and the herbicides diuron and tebuthiuron is most efficient when ferrioxalate is used. on the other hand, the degradation of malachite green and formaldehyde is not very influenced by the iron source showing only a slight improvement when ferrioxalate is used. In the case of formaldehyde, DCA, diuron and tebuthiuron, despite of the additional carbon introduced by the use of ferrioxalate, higher mineralization percentages were observed, confirming the beneficial effect of ferrioxalate on the degradation of these compounds. The degradation of tebuthiuron was studied in detail using a shallow pond type solar flow reactor of 4.5 L capacity and 4.5 cm solution depth. Solar irradiation of tebuthiuron at a flow rate of 9 L h(-1), in the presence of 10.0 mmol L-1 H2O2 and 1.0 mmol L-1 ferrioxalate resulted in complete conversion of this herbicide and 70% total organic carbon removal. (c) 2005 Elsevier Ltd. All rights reserved.

Effect of iron on bovine enamel and on the composition of the dental biofilm formed in situ

Objectives: This study investigated in situ the effect of iron (Fe) on the reduction of demineralization of bovine enamel, as well as on the composition of dental biofilm.Design and methods: Twelve volunteers were included in this blind crossover study, which was conducted in two stages of 14 days each. For each stage, the volunteers received palatal appliances containing four blocks of bovine enamel (4 mm x 4 mm x 2.5 mm). Six volunteers dripped a solution of 15 mmol L-1 ferrous sulphate onto the fragments and the remaining six dripped deionized water (eight times per day). After five minutes, a fresh 20% (w/v) sucrose solution was dripped onto all enamel blocks. During the experimental period the volunteers brushed their teeth with non-fluoridated dentifrice. After each stage, the percentage of surface microhardness change (%SMHC) and area of mineral toss (Delta Z) were determined on enamel and the dental biofilm formed on the blocks was collected and analysed for F, P, Ca, Fe and alkali-soluble carbohydrates. The concentrations of F, Ca and Fe in enamel were also analysed after acid biopsies.Results: There was a statistically significant increase in the P and Fe concentrations in the biofilms treated with ferrous sulphate (p < 0.05), which was not observed for F, Ca and alkali-soluble carbohydrates. The group treated with ferrous sulphate had significantly lower %SMHC and Delta Z when compared to control (p < 0.05).Conclusions: These results showed that ferrous sulphate reduced the demineralization of enamel blocks and altered the ionic composition of the dental biofilm formed in situ. (c) 2005 Elsevier Ltd. All rights reserved.

Characterization of iron(III)porphyrin-hydroxo complexes in organic media through UV-Vis and EPR spectroscopies

The interaction of OH- with Fe(TPP)(+), Fe(TDCPP)(+), Fe(TMP)(+) and Fe(TFPP)(+) in 1,2-dichloroethane was studied by titrating FeP solutions with aliquots of a solution of tetrabutylammonium hydroxide in acetonitrile. The number of OH- ions (n) coordinated to the FeP and the stability constants (beta(n)) for the FeP-OH- complexes were calculated from UV-Vis absorbance data and iron spin states were determined through EPR spectroscopy, Fe(TMP) (+) forms a high-spin mono-hydroxo complex, while Fe(TPP)I and Fe(TDCPP)(+) form high-spin bis-hydroxo complexes. To our knowledge, this is the first time that the formation of bis-hydroxo complexes from Fe(TPP) (+) has been reported, and this was possible because the studies were carried out in basic organic media, In this same medium, Fe-III-Fe-II reduction upon OH- addition to Fe(TFPP) (+) was observed, without concomitant formation of the mu-oxo dimeric species [Fe(TFPP)](2)O. (C) 1999 Elsevier B.V., All rights reserved.

Synthesis, characterization and electropolymerization of a new polypyrrole iron(II) Schiff-base complex

This work presents the synthesis of the complex [Fe(L)(2)](PF6)(2) (.) H2O (L = 2,6-bis[1-(3-pyrrol-1-yl-propylimino)ethyl]pyridine (Fig. 1) and its characterization through elemental and thermal analysis, X-ray diffraction and UV-Vis, IR and H-1 NMR spectra. The use of this compound in the preparation of modified electrodes is also described. The best electrochemical parameters to achieve optimum film formation have been established and the effects of both the upper-limit of the applied scanning potential (E-aul) and the number of scans on the efficiency of film formation have been investigated. Film surface morphology has been characterized by atomic force microscopy. (C) 2004 Elsevier Ltd. All rights reserved.

Low-temperature, self-nucleated growth of indium-tin oxide nanostructures by pulsed laser deposition on amorphous substrates

Indium-tin oxide nanostructures were deposited by excimer laser ablation in a nitrogen atmosphere using catalyst-free oxidized silicon substrates at 500 degrees C. Up to 1 mbar, nanowires grew by the vapor-liquid-solid (VLS) mechanism, with the amount of liquid material decreasing as the deposition pressure increased. The nanowires present the single-crystalline cubic bixbyite structure, oriented < 100 >. For the highest pressure used, pyramids were formed and no sign of liquid material could be observed, indicating that these structures grew by a vapor-solid mechanism. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Effect of presence of an acid catalyst on structure and properties of iron-doped siloxane-polyoxyethylene nanocomposites prepared by sol-gel

In this work we investigate the effect of hydrochloric acid (HC) addition on the structure and thermal and magnetic properties of iron-doped siloxane-polyoxyethylene (POE) hybrids prepared by the sol-gel route. X-ray powder diffraction (XRD) and X-ray absorption near edge structure (XANES) results reveal the dominance of ferrihydrite nanoparticles and a mixture of this phase with FeCl4- species in the hybrid prepared without and with HCl, respectively. Thermal analysis reveals the existence of two crystalline polymeric phases in the hybrid prepared with HCl whereas hybrids prepared without HCl are amorphous. The 105 and 60 Angstrom sized ferrihydrite nanoparticles were detected by SAXS analysis of the composite prepared without and with HCl, respectively. The magnetic results suggest that in both samples antiferromagnetic nanoparticles coexist with small clusters/isolated ions. In the sample without HCl addition, larger particles dominate the magnetic behavior, while the opposite occurs for the sample prepared using HCl catalyst. (C) 2004 Elsevier B.V. All rights reserved.

Effect of an iron mouthrinse on enamel and dentine erosion subjected or not to abrasion: An in situ/ex vivo study

Objectives: This in situ/ex vivo study evaluated whether a rinse with an iron solution could reduce wear and the percentage of microhardness change of human enamel and dentine submitted to erosion followed by brushing after 1 or 30 min.Design: During 2 experimental 5-day crossover phases (wash-out period of 10 days), 10 volunteers wore intraoral palatal devices, with 12 specimens (6 of enamel and 6 of dentine) arranged in 3 horizontal rows (4 specimens each). In one phase, the volunteers immersed the device for 5 min in 150 mL of cola drink, 4 times a day. Immediately after immersion, no treatment was performed in one row. The other row was brushed after 1 min using a fluoride dentifrice and the device was replaced into mouth. After 30 min, the remaining row was brushed. In the other phase, the procedures were repeated, but after immersion the volunteers rinsed for 1 min with 10 mL of a 10 mM ferrous sulphate solution. Changes in surface microhardness (%SMH) and wear (profilometry) of enamel and dentine were measured. Data were tested using ANOVA and Tukey's tests (p < 0.05).Results: the enamel presented more wear than dentine, under all experimental conditions. The iron solution caused a significant reduction on the %SMH in enamel, and a significant reduction on the wear in dentine, regardless the other conditions.Conclusions: Rinsing with an iron solution after an erosive attack, followed or not by an abrasive episode, may be a viable alternative to reduce the loss of dental structure. (c) 2006 Elsevier Ltd. All rights reserved.

Preparation and properties of colloidal particles. Silica on yttrium iron garnet

Various properties of particles can be altered by coating them with a layer of different chemical composition. Yttrium iron garnet (YIG) particles has been coated with silica for control of their sintering, corrosion resistance, and stabilization of magnetic properties. This silica cover was obtained by hydrolysis of tetraethylorthosilicate (TEOS) in 2-propanol. This material was characterized by transmission (TEM) electron microscopy, (XEDS) X-ray energy-dispersive spectrometry, (XPS) X-ray photoemission spectroscopy and (VSM) vibrating sample magnetometry. YIG was heterocoagulated by silica as indicated by TEM micrographies. XPS measurements indicated that only binding energy for silicon and oxygen was found on the silica shell, which confirms that the YIG was covered. The values of the saturation magnetization differ from the heterocoagulated system to well-crystallized YIG.

Influence of Environmental Conditioning on the Shear Behavior of Poly(phenylene sulfide)/Glass Fiber Composites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Development and Evaluation of a Nanoporous Iron (Hydr)oxide Electrode for Phosphate Sensing

Nanoporous iron (hydr) oxide electrodes are evaluated as phosphate sensors using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The intensity of the reduction peak current (I-cp) of the ferrihydrite working electrode is tied to phosphate concentration at low pH; however, a hematite electrode combined with the use of EIS provided reliable sensing data at multiple pH values. Nanoporous hematite working electrodes produced an impedance phase component (theta) that shifts with increasing phosphate, and, at chosen frequencies, theta values were fitted for the range 1 nM to 0.1 mM phosphate at pH 4 and pH 7 in 5 mM NaClO4.

Enhanced Eu3+ Emission in Aqueous Phosphotungstate Colloidal Systems: Stabilization of Polyoxometalate Nanostructures

Luminescent Eu3+-containing polyphosphate tungstate aqueous colloidal systems were prgared and studied as a function of the relative polyphosphate tungstate content. In polyphosphate-rich solutions, Eu-H- ions occupy cagelike sites composed of phosphate groups from the metaphosphate chains. In these sites, an average number of 0.5 water molecule coordinates to an Eu3+ ion and the 500 emission quantum efficiency is 0.22. Tungstatc addition leads to important modifications in neighboring Eu3+ leading to coordination sites in the aqueous medium where metal ions are completely hidden from interactions with solvent molecules. Transmission electron microscopy results clearly show \V-rich nanoparticles with sizes between 5 and 10 nm for all tungstate relative concentrations. For high tungstatc relative contents (above 30 mol %), spectroscopic results suggest the presence of Eu34- in polyoxometalate (P0M)-like sites by comparison with the well-known decatungstoeuropate [EuW10O36](9-) structure. These new aqueous colloids display surprisingly high 5llo emission quantum efficiencies of ca 80% because of the strong ligand field provided by tungstate POM ligands and the complete absence of water molecules from the Eu3+ first coordination shell.

Transplacental Transfer of Iron in the Water Buffalo (Bubalus bubalis): Uteroferrin and Erythrophagocytosis

The objectives of this investigation were to understand transplacental transport of iron by secreted uteroferrin (UF) and haemophagous areas of water buffalo placenta and clarify the role(s) of blood extravasation at the placental-maternal interface. Placentomes and interplacentomal region of 51 placentae at various stages of gestation were fixed, processed for light and transmission electron microscopy, histochemistry and immunohistochemistry. Haemophagous areas were present in placentomes collected between 4 and 10 months of pregnancy. Perl's reaction for ferric iron was negative in placentomes, but positive in endometrial glands. Positive staining for UF indicated areas in which it was being taken up by phagocytosis and/or fluid phase pinocytosis in areolae of the interplacentomal mesenchyme, with little staining in endometrial stroma. Imunohistochemistry detected UF in trophectoderm of haemophagous regions of placentomes and in other parts of the foetal villous tree, but the strongest immunostaining was in the epithelial cells and lumen of uterine glands. Ultrastructural analyses indicated that erythrophagocytosis was occurring and that erythrocytes were present inside cells of the chorion that also contained endocytic vesicles and caveolae. Results of this study indicate that both the haemophagous areas of placentomes and the areolae at the interface between chorion and endometrial glands are important sites for iron transfer from mother to foetal-placental tissues in buffalo throughout pregnancy.

Organic complexation and translocation of ferric iron in podzols of the Negro River watershed. Separation of secondary Fe species from Al species

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Construction and application of an electrochemical sensor for paracetamol determination based on iron tetrapyridinoporphyrazine as a biomimetic catalyst of P450 enzyme

This work describes the construction and application of a biomimetic sensor for paracetamol determination in different samples. The sensor was prepared by modifying a glassy carbon electrode surface with a Nafion (R) membrane doped with FeTPyPz. The best performance of the sensor in 0.1 mol L-1 acetate buffer was at pH 3.6. Under these conditions, an oxidation potential of paracetamol was observed at 445 mV vs. Ag vertical bar AgCl. The sensor presented a linear response range between 4.0 and 420 mu mol L-1, a sensitivity of 46.015 mA L mol(-1) cm(-2), quantification and detection limits of 4.0 mu mol L-1 and 1.2 mu mol L-1, respectively. A detailed investigation about its electrochemical behavior and selectivity was carried out. The results suggested that FeTPyPz presents catalytic properties similar to P450 enzyme for paracetamol oxidation. Finally, the sensor was applied for paracetamol determination in commercial drugs and for the monitoring of its degradation in an electrochemical batch reactor effluent.