Composites based on iron supported on high surface area activated carbon were prepared and characterized with
57Fe 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
3O
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
°C under N
2 atmosphere, and then reused for several consecutive times.
Cobalt- and manganese-substituted ferrites were used as heterogeneous catalysts for liquid-phase aerobic oxidation of various monoterpenic alkenes. The materials were prepared by co-precipitation and ...characterized by Mössbauer spectroscopy, powder X-ray diffractometry, magnetization measurements, and elemental analysis. The results show that isomorphic substitution of iron in the ferrite crystalline structure occurred preferentially at octahedral positions and strongly affected its catalytic properties in the oxidation of monoterpenes. Various valuable oxygenated monoterpenic compounds were obtained with high combined selectivities (75–95%) at ca. 40% substrate conversions. Oxidations of
β-pinene and 3-carene led almost exclusively to allylic mono-oxygenated derivatives, whereas limonene and
α-pinene gave both epoxides and allylic products. The use of inexpensive catalyst and oxidant, solvent-free conditions, and high final product concentrations (ca. 40 wt%) are significant practical advantages of this environmentally friendly process. The catalysts undergo no metal leaching and can be easily recovered by the application of an external magnet and reused.
The pseudomorphic transformation of magnetite into hematite (martitization) is widespread in geological environments, but the process and mechanism of this transformation is still not fully ...understood. Micro- and nano-scale techniques—scanning electron microscopy, focused ion bean transmission electron microscopy, and Raman spectroscopy—were used in combination with X-ray diffraction, Curie balance and magnetic hysteresis analyses, as well as Mössbauer spectroscopy on martite samples from a banded iron formation (2.9 Ga, Dharwar Craton, India), and from lateritic soils, which have developed on siliciclastic and volcanic rocks previously affected by metamorphic fluids (Minas Gerais, Brazil). Octahedral crystals from both samples are composed of hematite with minor patches of magnetite, but show different structures. The Indian crystals show trellis of subhedral magnetite hosting maghemite in sharp contact with interstitial hematite crystals, which suggests exsolution along parting planes. Grain boundary migrations within the hematite point to dynamic crystallization during deformation. Dislocations and fluid inclusions in hematite reflect its precipitation related to a hydrothermal event. In the Brazilian martite, dislocations are observed and maghemite occurs as Insel structures and nano-twin sets. The latter, typical for the hematite, are a transformation product from maghemite into hematite. For both samples, a deformation-induced hydrothermally driven transformation from magnetite via maghemite to hematite is proposed. The transformation from magnetite into maghemite comprises intermediate non-stoichiometric magnetite steps related to a redox process. This study shows that martite found in supergene environment may result from earlier hypogene processes.
Either pressing or solvent extraction of
Jatropha curcas
seed oil results in great amounts of cake as a byproduct. The direct use of these fresh biomasses threats the health of mammals as they ...contain phorbol esters (PEs), a highly toxic class of substance. Five different treatments were bench-assayed to degrade PEs: (i) ammonium hydroxide, (ii) urea, (iii) heat, (iv) ultraviolet radiation, and (v) gamma radiation. All used methods were evaluated for their efficiency on removing PEs from the biomass resulting from deoiling seeds of
J. curcas
. The treatments were variably effective in reducing PEs contents to nontoxic levels. Aqueous ammonium hydroxide solution (3% w/w) at 70 °C was found to reduce the contents of PEs down to 0.084 mg g
−1
(cake) and 0.083 mg g
−1
(bran). The treatment with an aqueous solution NH
4
OH 7% w/w with heating at 90 °C led to the most effective reduction, rendering PEs contents as low as 0.063 mg g
−1
(cake) and 0.066 mg g
−1
(bran). These are below the critical toxicity threshold, namely 0.1 mg g
−1
, which is found in seeds of nontoxic
J. curcas
varieties. The corresponding results from cytotoxicity tests and assessments of nutritional characteristics confirmed that these treated samples have become safe enough, making this affordable technology potentially scalable to be used in the feeding of livestock at the industrial level.
The ceramic materials industry has vast potential for use of waste from industrial processes, such as iron mining tailings. The aim of this study was to test technological use of tailings samples ...from the dam rupture of the Samarco S.A. Company in 2015 to produce structural ceramics. Sedimentation and flotation processes were used to improve their characteristics, analyzing their chemical and mineralogical composition and granulometry. We produced 48 samples with a mixture of soil and residues in proportions of 10, 20, and 30 wt%, with sintering at 950 °C. The results showed that co-processing of iron mining tailings can be considered viable for improving certain aspects of some technological properties. The maximum amount of residue used was 30 wt% for any of the fractions used, as above this concentration the specimens lose important characteristics.
The conversion of solar energy into hydrogen fuel by splitting water into photoelectrochemical cells (PEC) is an appealing strategy to store energy and minimize the extensive use of fossil fuels. The ...key requirement for efficient water splitting is producing a large band bending (photovoltage) at the semiconductor to improve the separation of the photogenerated charge carriers. Therefore, an attractive method consists in creating internal electrical fields inside the PEC to render more favorable band bending for water splitting. Coupling ferroelectric materials exhibiting spontaneous polarization with visible light photoactive semiconductors can be a likely approach to getting higher photovoltage outputs. The spontaneous electric polarization tends to promote the desirable separation of photogenerated electron- hole pairs and can produce photovoltages higher than that obtained from a conventional p-n heterojunction. Herein, we demonstrate that a hole inversion layer induced by a ferroelectric Bi4V2O11 perovskite at the n-type BiVO4 interface creates a virtual p-n junction with high photovoltage, which is suitable for water splitting. The photovoltage output can be boosted by changing the polarization by doping the ferroelectric material with tungsten in order to produce the relatively large photovoltage of 1.39 V, decreasing the surface recombination and enhancing the photocurrent as much as 180%.
A soil material containing 81% Fe2O3 that is inactive towards H2O2 was used to prepare composites with charcoal obtained from sucrose. Composites obtained by heating under air at 400, 600, 700 and ...800°C were characterized by total Fe, Fe2+ and Fe3+ chemical analyses, Mössbauer spectroscopy, visible diffuse reflectance, X-ray diffraction and surface area determination. The catalytic activities of the composites were monitored by methylene blue degradation. The results indicate that the activity towards methylene blue degradation was strongly enhanced after heating at 600°C, with almost 100% color removal. Fe2+ in the magnetite structure was mainly responsible for the catalytic activity the composites and the mechanism of methylene blue degradation beginning via OH radicals produced by Fe2+ in the magnetite structure and H2O2. The proposed mechanism is supported by ESI-MS analysis.
The chemical preparation of a tin-doped spinel ferrite via the co-precipitation method rendered a sample containing 48.2
mass% Fe
3+, 11.8
mass% Fe
2+ and 13.0
mass% Sn. Powder X-ray diffractometry ...data collected with synchrotron radiation source revealed the co-existence of two crystallographic phases: one with cubic (spatial group,
Fd3
m) spinel and other with trigonal–hexagonal (
R
3
¯
c
) structure.
57Fe Mössbauer spectroscopy analysis confirmed the occurrence of two tin-doped phases, with relative spectral areas of 50.6% and 49.4%; deduced chemical structures of these two phases correspond to
(
F
e
3
+
,
F
e
2
+
)
2.44
S
n
0.43
4
+
⊕
0.13
O
4
and
α
-F
e
1.88
3
+
S
n
0.12
4
+
O
3
, (⊕, cation vacancy), respectively. The measured value for saturation magnetization
σ
=
30
J
T
−1
kg
−1 for this sample leads to a Sn
4+-ferrite with
σ
=
60
J
T
−1
kg
−1. The magnetic hyperfine field detected with
119Sn Mössbauer spectroscopy was interpreted as being due to a supertransferred magnetic moment from iron cations to Sn
4+ in octahedral sites of these iron oxides lattices.
The approach proposed here is focused on the separation of light fractions (corresponding to fatty acids with molecular chains between 8 to 14 carbons) from the fatty acid methyl esters (FAMES) of ...the biodiesel obtained by the reaction of transesterification of triacylglycerol’s in the kernel gueiroba oil (Syagrus oleracea) with methanol. The whole biodiesel was fractionated through atmospheric distillation in a single glass column with thermal insulation. Such a separation produced 59.79% in volume of light biodiesel (LB), which was mixed with the standard mineral Jet-A1 kerosene (cf. ASTM, corresponding to the QAV-1, cf. the Brazilian standard of the ANP) for aviation, in the volumetric ratios LB:Jet-A1 2:98; 5:95; 10:90 and 20:80. The values of density, water content, distillation analysis, flash point, calorific value and freezing point were carefully checked for their compliance with the official recommendations for a jet fuel. It was found that the mixtures richest in the Jet-A1 mineral kerosene, that is, those containing no more than 5% LB by volume, well meet the recommended standards and are technologically viable to replace pure Jet-A1 kerosene for the propulsion of turbine aircraft.
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