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J D Fabris - One of the best experts on this subject based on the ideXlab platform.
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synthesis and thermal treatment of cu doped Goethite oxidation of quinoline through heterogeneous fenton process
Applied Catalysis B-environmental, 2009Co-Authors: Iara R Guimaraes, Luiz C A Oliveira, Amanda S Giroto, Mario Cesar Guerreiro, Diana Q Lima, J D FabrisAbstract:Samples of Cu-doped Goethites were prepared and characterized by Mossbauer spectroscopy, XRD, TPR and BET surface area measurements. Mossbauer data showed the incorporation of Cu2+ in the Goethite structure, and this cation-doping caused a significant decrease of the chemical reduction temperature in the TPR process. The catalytic behavior of these Fe1−xCuxOOH materials was investigated for the H2O2 decomposition to O2 and the Fenton-like reaction to oxidize quinoline. It was observed that Cu2+ in this Goethite and also the thermal treatment with H2 produced a strong increase in the catalytic activity during the quinoline oxidation. The successive hydroxylation of quinoline during this oxidation strongly suggests that highly reactive hydroxyl radicals are generated during the reaction involving H2O2 on the Cu-Goethite grain surface, also confirming that these materials are efficient heterogeneous Fenton catalysts.
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catalytic properties of Goethite prepared in the presence of nb on oxidation reactions in water computational and experimental studies
Applied Catalysis B-environmental, 2008Co-Authors: Luiz C A Oliveira, Teodorico C Ramalho, Eugenio F De Souza, Maraisa Goncalves, Diana Q L Oliveira, Marcio C Pereira, J D FabrisAbstract:Abstract Nb-substituted Goethites have been prepared and characterized by Mossbauer spectroscopy, XRD, FTIR and BET surface area measurements. The doublet formation in Mossbauer spectra and the decreasing of the crystallinity shown in XRD analyses indicated that the Fe domain size is small, which may be the result of either Fe3+ substitution for Nb5+ in the Goethite structure or simply the formation of small particle-size Goethite when Nb is present. FTIR analyses showed shifts and broadening of the bands as result of the incorporation of Nb5+ ions into the α-FeOOH structure. The insertion of Nb in the Goethite structure caused a significant increase in the BET surface area of the material. The prepared materials were investigated for the H2O2 decomposition and the Fenton reaction in the oxidation of methylene blue dye. It was observed that the introduction of Nb during the synthesis of Goethite produced a strong increase in the activity for the dye contaminant oxidation by H2O2. Theoretical quantum DFT calculations were carried out in order to understand the degradation mechanism for methylene blue with Goethites.
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minerals in the clay fraction of brazilian latosols oxisols a review
Clay Minerals, 2008Co-Authors: J D FabrisAbstract:This review focuses on the clay mineralogy of the most important Brazilian soils: the Latosols, which cover >60% of the country by area, and occur in association with other soils. They are typically deep, highly-weathered soils, dominated by low-activity 1:1 clay minerals and Fe and Al oxyhydroxides, with varying proportions of these minerals, depending on parent material and weathering intensity. They are usually of low fertility, although eutric types also occur. Latosols are generally correlated with Oxisols (American soil taxonomy) and Ferralsols (WRB system). Clay mineralogy is typically monotonous: kaolinite, gibbsite, hematite, Goethite, maghemite and Ti minerals (mainly ilmenite and anatase) are the prominent mineral phases in the clay fraction. Some Latosols developing on basalt from southern Brazil contain significant amounts of hydroxyl-interlayed vermiculite. Among the pedogenic oxides the most frequent are Goethite (α-FeOOH), indicated by yellowish colours (2.5Y–10YR; in the absence of hematite), and hematite (α-Fe2O3), which imbues reddish colors (2.5YR–5R), even when present in very minor amounts. Maghemite (γ-Fe2O3) is less frequent; it imparts a reddish-brown colour (5YR–2.5YR) and magnetic properties. Both Goethite and hematite show Al-substitution, with a greater relative proportion in soil Goethites. Hence, in similar drainage conditions, Goethite is less prone to dissolution than hematite. Most reddish Latosols also contain maghemite, due to partial or complete oxidation of magnetite, which generally occurs naturally or is fire-induced. Magnetite and/or maghemite are associated with trace elements which are important in plant nutrition, such as Cu, Zn and Co. The contents of gibbsite in Latosols are extremely variable, from a complete absence in brown Latosols, to 54% in red Latosols from mafic rocks. Relatively large amounts of gibbsite are found in the clay fraction of these soils and this mineral is important in P sorption in deeply weathered Latosols in association with Goethite and hematite. Even though most Latosols are dystrophic, some are eutrophic, revealing an unusually large base saturation in areas under ustic regimes where the parent material is particularly rich in bases, such as basalts. This eutrophic nature is attributed to the protecting role of micro-aggregates in ferric red Latosols, which retard base-leaching from the inner aggregate. At the other extreme, some Brazilian Latosols are acric and positively-charged in sub-surface horizons, as revealed by the relationship pH KCl > pH H2O. These acric Latosols are the result of long-term weathering and intensive leaching, during which pH tends to increase to values close to the zero point charge of Fe and Al oxides (between 6 and 7), greatly increasing P adsorption, which is mainly attributed to gibbsite, Goethite and hematite. Soil kaolinites in Brazilian Latosols are mostly of low crystallinity, with Hughes and Brown indexes of between 6 and 15. In this review we have discussed the role of these clay-fraction minerals in soil genesis and fertility, highlighting the marked role of inheritance from deeply-weathered parent material. Latosols typically retain large amounts of Fe oxides, some of which are magnetic, with spontaneous magnetization >1 J T−1 kg−1. In this regard, reddish Latosols developed from mafic rocks are the most representative magnetic soils, and cover as much as 3.9% of Brazil. An overview of magnetic soils on four representative examples of mafic lithologies is presented, together with some aspects of their Fe-oxide mineralogy and related field and laboratory technqiues.
S B Weed - One of the best experts on this subject based on the ideXlab platform.
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phosphate adsorption by clays from brazilian oxisols relationships with specific surface area and mineralogy
Geoderma, 1996Co-Authors: Mauricio Paulo Ferreira Fontes, S B WeedAbstract:Oxisols derived from clayey sediments, sandstone, mafic rocks and schist were sampled in the “Triangulo Mineiro” region, Minas Gerais State, Brazil, to study the relationship between the phosphate adsorption and mineralogy and specific surface area. The specific surface area of the iron oxides estimated from N2 adsorption by the soil clays before and after dithionite-citrate dissolution of the Fe-oxides ranged from 45 to 110 m2 g−1. Specific surface area of the iron oxides correlated to the Goethite: Goethite +hematite ratio (r = 0.694∗). Specific surface area estimated by differential X-ray analysis did not show good agreement with BET-N2 adsorption values. Phosphate adsorption maxima for the soil clays (< 2 μm) ranged from about 70 to 160 μmol P g−1 of clay. Stepwise regression analysis showed phosphate adsorption for the total clays to be primarily related to Goethite, gibbsite, the sum of Fe plus Al oxides and also amorphous Al oxides. A mild treatment for concentrating the soil iron oxides showed small effect in the phosphate adsorption for most soils. It showed the importance of gibbsite and crystalline Fe-oxides in the adsorption, with Goethite explaining most of the variation occurring in P adsorption after the treatment. Correlation studies showed the adsorption capacity per unit specific surface to be somewhat dependent on variations in the iron oxide mineralogy of the clay samples. Clay color showed good correlation to the Goethites: (Goethite + hematite) ratio in soils but no direct relationship between phosphate adsorption and clay color was detected.
Mario Villalobos - One of the best experts on this subject based on the ideXlab platform.
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Goethite surface reactivity ii a microscopic site density model that describes its surface area normalized variability
Journal of Colloid and Interface Science, 2009Co-Authors: Mario Villalobos, Marcos A Cheney, Jorge AlcarazcienfuegosAbstract:Abstract The model described in this investigation explains the variable macroscopic surface reactivity of different Goethite preparations when adsorption data are normalized by surface area, especially the high reactivity of low specific surface area Goethites. A simplified model of crystalline face distributions for each of the Goethite preparations, in combination with experimental maximum chromate adsorption values previously determined, allowed a crystallographic site-density analysis that would explain the latter values. In addition, a surface complexation modeling approach was coupled to the previous model and provided individual affinity constants for proton and ion binding for singly, doubly, and triply coordinated surface sites. The proposed microscopic model is able to accurately describe the macroscopic adsorption behavior of protons, carbonate, chromate, and lead(II) ions on three Goethites of specific surface areas of 50, 70, and 94 m2/g, using the same affinity constants. The model results indicate that the surface of high specific surface area nanoparticulate Goethites may be described mostly as a combination of (1 0 1) and (0 0 1) faces, with reactive singly and triply coordinated surface oxygen sites; while the model for low specific surface area Goethites requires, in addition to one of the above faces, a variable but high degree of (0 1 0)/(2 1 0) faces containing high surface densities of reactive singly and doubly coordinated oxygen groups. The model is potentially very useful and may be applied to any Goethite provided its maximum ion adsorption capacity and proton charging behavior are known.
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Goethite surface reactivity a macroscopic investigation unifying proton chromate carbonate and lead ii adsorption
Journal of Colloid and Interface Science, 2008Co-Authors: Mario Villalobos, Ayax PerezgallegosAbstract:The Goethite surface structure has been extensively studied, but no convincing quantitative description of its highly variable surface reactivity as inversely related to its specific surface area (SSA) has been found. The present study adds experimental evidence and provides a unified macroscopic explanation to this anomalous behavior from differences in average adsorption capacities, and not in average adsorption affinities. We investigated the chromate anion and lead(II) cation adsorption behavior onto three different Goethites with SSA varying from 50 to 94 m2/g, and analyzed an extensive set of published anion adsorption and proton charging data for variable SSA Goethites. Maximum chromate adsorption was found to occupy on average from 3.1 to 9.7 sites/nm2, inversely related to SSA. Congruency of oxyanion and Pb(II) adsorption behavior based on fractional site occupancy using these values, and a site density analysis suggest that: (i) ion binding occurs to singly and doubly coordinated sites, (ii) proton binding occurs to singly and triply coordinated sites (ranging from 6.2 to 8 total sites/nm2, in most cases), and (iii) a predominance of (210) and/or (010) faces explains the high reactivity of low SSA Goethites. The results imply that the macroscopic Goethite adsorption behavior may be predicted without a need to investigate extensive structural details of each specific Goethite of interest.
Jorge Alcarazcienfuegos - One of the best experts on this subject based on the ideXlab platform.
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Goethite surface reactivity ii a microscopic site density model that describes its surface area normalized variability
Journal of Colloid and Interface Science, 2009Co-Authors: Mario Villalobos, Marcos A Cheney, Jorge AlcarazcienfuegosAbstract:Abstract The model described in this investigation explains the variable macroscopic surface reactivity of different Goethite preparations when adsorption data are normalized by surface area, especially the high reactivity of low specific surface area Goethites. A simplified model of crystalline face distributions for each of the Goethite preparations, in combination with experimental maximum chromate adsorption values previously determined, allowed a crystallographic site-density analysis that would explain the latter values. In addition, a surface complexation modeling approach was coupled to the previous model and provided individual affinity constants for proton and ion binding for singly, doubly, and triply coordinated surface sites. The proposed microscopic model is able to accurately describe the macroscopic adsorption behavior of protons, carbonate, chromate, and lead(II) ions on three Goethites of specific surface areas of 50, 70, and 94 m2/g, using the same affinity constants. The model results indicate that the surface of high specific surface area nanoparticulate Goethites may be described mostly as a combination of (1 0 1) and (0 0 1) faces, with reactive singly and triply coordinated surface oxygen sites; while the model for low specific surface area Goethites requires, in addition to one of the above faces, a variable but high degree of (0 1 0)/(2 1 0) faces containing high surface densities of reactive singly and doubly coordinated oxygen groups. The model is potentially very useful and may be applied to any Goethite provided its maximum ion adsorption capacity and proton charging behavior are known.
Lynn E Katz - One of the best experts on this subject based on the ideXlab platform.
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capturing the variable reactivity of Goethites in surface complexation modeling by correlating model parameters with specific surface area
Geochimica et Cosmochimica Acta, 2019Co-Authors: Joonkyoung Han, Lynn E KatzAbstract:Abstract The development of predictive tools capable of simulating adsorption behavior on Goethite (α-FeOOH) surfaces has evolved over the past several decades. Recent research has focused on capturing the variation of surface reactivity and adsorption behavior for different preparations of synthetic Goethites. In this research, an approach to estimate modeling parameters based on the specific surface area (SSA) of Goethites was established and combined with a Charge Distribution – Multi-site Complexation (CD-MUSIC) surface complexation model. It was assumed that differences in crystal face contributions (CFC), inner-Helmholtz capacitances (C1), and protonation constants of surface oxygens (pKa’s) among different preparations of Goethite contribute to the variation of surface reactivity. Thus, correlations of these modeling parameters with the SSA of a range of Goethites were identified by comprehensively combining microscopic, macroscopic, and modeling data reported in literature along with adsorption data collected from macroscopic experiments conducted as part of this study. A CD-MUSIC model shown to be capable of accurately predicting adsorption for several metal ions and oxyanion selenite on a 62.9 m2/g SSA Goethite served as the basis for the development of the adsorption modeling approach described in this paper. The predictive capability of the newly developed modeling approach was verified by comparing predictions of protons, SeO32−, and Cd2+ adsorption with experimental data from Goethites with SSAs ranging between 21.3 and 105 m2/g; in total, 40 adsorption data sets from 13 different Goethites were used for model verification. The results from this study indicate that the variation of surface reactivity of Goethites can be successfully simulated by changing CFC, C1, and pK2,singly (i.e. second protonation constant of singly-coordinated oxygens on the Goethite surface) based on the SSA, which implies that self-consistent adsorption parameters can be applied to predict adsorption behavior over a range of Goethite preparations.