Tesis de ,aestria presentadas en la facultad de ciencia y tecnologia, Universidad Pedagogica Nacional.

Tesis de maestria

Environmental implications and applications of engineered nanoscale magnetite and its hybrid nanocomposites: A review of recent literature.

The present state of the methods commonly used for inorganic and mineral matter characterization in coal is described and summarized. The application of various separation procedures, macroscopic observations, reflected and transmitted optical microscopy, scanning and transmission electron microscopy, X-ray diffraction, differential thermal and thermogravimetric analyses, Mossbauer spectroscopy, infrared spectroscopy, and chemical analyses are briefly discussed. A short critical overview on the advantages and limitations of the above listed methods as well as some recommendations during their utilization are also presented.

Methods for characterization of inorganic and mineral matter in coal: A critical overview

The discovery of mutated palynomorphs in end-Permian rocks led to the hypothesis that the eruption of the Siberian Traps through older organic-rich sediments synthesized and released massive quantities of organohalogens, which caused widespread O 3 depletion and allowed increased terrestrial incidence of harmful ultraviolet-B radiation (UV-B, 280–315 nm; Visscher et al . 2004 Proc. Natl Acad. Sci. USA 101 , 12 952–12 956). Here, we use an extended version of the Cambridge two-dimensional chemistry–transport model to evaluate quantitatively this possibility along with two other potential causes of O 3 loss at this time: (i) direct effects of HCl release by the Siberian Traps and (ii) the indirect release of organohalogens from dispersed organic matter. According to our simulations, CH 3 Cl released from the heating of coals alone caused comparatively minor O 3 depletion (5–20% maximum) because this mechanism fails to deliver sufficiently large amounts of Cl into the stratosphere. The unusual explosive nature of the Siberian Traps, combined with the direct release of large quantities of HCl, depleted the model O 3 layer in the high northern latitudes by 33–55%, given a main eruptive phase of less than or equal to 200 kyr. Nevertheless, O 3 depletion was most extensive when HCl release from the Siberian Traps was combined with massive CH 3 Cl release synthesized from a large reservoir of dispersed organic matter in Siberian rocks. This suite of model experiments produced column O 3 depletion of 70–85% and 55–80% in the high northern and southern latitudes, respectively, given eruption durations of 100–200 kyr. On longer eruption time scales of 400–600 kyr, corresponding O 3 depletion was 30–40% and 20–30%, respectively. Calculated year-round increases in total near-surface biologically effective (BE) UV-B radiation following these reductions in O 3 layer range from 30–60 (kJ m −2  d −1 ) BE up to 50–100 (kJ m −2  d −1 ) BE . These ranges of daily UV-B doses appear sufficient to exert mutagenic effects on plants, especially if sustained over tens of thousands of years, unlike either rising temperatures or SO 2 concentrations.

The stability of the stratospheric ozone layer during the end-Permian eruption of the Siberian Traps

Modeling of adsorption of Methylene Blue dye on Ho-CaWO4 nanoparticles using Response Surface Methodology (RSM) and Artificial Neural Network (ANN) techniques.

In this work, we studied the catalytic activity, structural properties, and behavior of a Fe3O4 magnetic system. The Fe3O4 nanoparticles were prepared by the thermal decomposition method. X-ray diffraction confirmed the presence of a structural Fe3O4 phase, where acicular shape of the grains is shown. Transmission Mossbauer spectroscopy showed a wide distribution of particle sizes at room temperature, some of these present superparamagnetic behavior and are responsible of paramagnetic sites. The hysteresis loops obtained by the use of a vibrating sample magnetometer showed that these nanoparticles exhibit superparamagnetic behavior. However, the cycles present a significant contribution from a ferrimagnetic component at 2 K, which agrees with Mossbauer results. Through scanning electron microscopy, a tendency to the agglomeration of nanoparticles was observed. Nanoparticle activity in the degradation of methylene blue (MB) was studied through fluorescence spectroscopy, finding dye adsorption properties.

https://iopscience.iop.org/article/10.1088/1742-6596/614/1/012007/pdf

Preparation of Fe3O4 Nanoparticles and Removal of Methylene Blue through Adsorption

We report on the magnetic properties of Fex Mn0.3 Al0.7-x (0.275 ≤ x ≤ 0.525) disordered alloys, which were investigated by means of Mossbauer spectroscopy, ac magnetic susceptibility and magnetization measurements. Our results are summarized in a magnetic phase diagram which includes both a re-entrant spin glass-ferromagnetic transition line for x > 0.425 and a re-entrant spin glass-antiferromagnetic transition line for x < 0.375.

Magnetic properties of FexMn0.3Al0.7-x (0.275 ≤ x ≤ 0.525) disordered alloys

A methodology to evaluate coal ash content using Siderite Mössbauer spectral area

Mössbauer and magnetization evidence of spin-glass phase in the Fe0.45Mn0.25Al0.30 disordered alloy

The magnetic properties of the FexMn0.600 −xAl0.400(0.200 ≤ x ≤ 0.600) disordered alloys were investigated by means of Mossbauer spectrometry, ac magnetic susceptibility, and ac calorimetry measurements. Our results are summarized in a magnetic phase diagram, which includes an antiferromagnetic phase for x ≤ 0.300 at T ≤ 225 K, a ferromagnetic one for x ≥ 0.425 at T ≤ 340 K, and a paramagnetic phase for high temperatures and all the compositions. This phase diagram also shows for the first time both a re-entrant spin-glass–ferromagnetic transition line for x ≥ 0.425 and T ≤ 60 K and a re-entrant spin-glass–antiferromagnetic one for x ≤ 0.300 and T ≤ 40 K. The occurrence of superparamagnetic-like blocked events (for 0.300 ≤ x ≤ 0.600 and at T ≈ 200 K) is associated with the presence of Fe-rich magnetic clusters which can originate from the disordered atomic character of the alloys.

http://iopscience.iop.org/article/10.1088/0953-8984/14/25/320/pdf

Jesús A. Tabares

Papers

Preparation of Fe3O4 Nanoparticles and Removal of Methylene Blue through Adsorption

Magnetic properties of FexMn0.3Al0.7-x (0.275 ≤ x ≤ 0.525) disordered alloys

A methodology to evaluate coal ash content using Siderite Mössbauer spectral area

Mössbauer and magnetization evidence of spin-glass phase in the Fe0.45Mn0.25Al0.30 disordered alloy

Magnetic properties of the FexMn0.600 −xAl0.400, 0.200 ≤ x ≤ 0.600,disordered alloy series