Seminarios Prof. Hélio A. Duarte - U. F. Minas Gerais, Brasil

[fisquim LACSUMP]

Estimados,

Tenemos el agrado de invitarlos a los Seminarios que dictará el Prof.
Hélio A. Duarte del Dpto. de Química de la UNIVERSIDADE FEDERAL DE MINAS
GERAIS, quien nos visita en el marco del Programa de Centros Asociados de
Posgrado Brasil-Argentina CAPES-SPU.

El evento se llevará a cabo en el Aula 34 del Departamento de Física, en
el Bloque II, segundo piso, el Viernes 10 de abril, a partir de las 10
horas.

10:00 hs - 1º Seminario:
*“Nanotubos de Minerales de Arcilla– Un estudio SCC-DFTB (Self
Consistent Charge – Density Functional – Tight Binding method).” *
11:00 hs - coffee-break

11:30 hs - 2º Seminario: *“Reactividad de la Superficie de Sulfatos
Minerales – Un Estudio DFT (Density Functional Theory)"*

Los esperamos!

Resúmenes de los seminarios:

*            Clay mineral nanotubes – A SCC-DFTB Study*



The emerging field of nanotechnology is mostly focused on carbon and
inorganic based nanomaterials, such as carbon nanotubes, graphene,
transition metal nanotubes and nanowires. Naturally occurring clay minerals
form also nanostructured layered materials and nanotubes with remarkable
geometric properties. Since 2000, imogolite, halloysite and chrysotile
gained prominence in the literature and appear as an emerging field of
research as it can be used as nanoreactors for selective catalysts,
adsorbent, nanocable, support for the immobilization of metalloporphyrins,
encapsulation, ion conductor and component in composites. The clay mineral
nanotubes can be easily synthesized in mild conditions, functionalized and
chemically modified. Therefore, they are an important target for developing
advanced materials.

We have investigated through the Self Consistent Charge – Density
Functional – Tight Binding (SCC-DFTB) approximated method the imogolite,
halloysite and chrysotile nanotubes providing insights about their
stability, electronic, structural and mechanical properties. Imogolite-like
aluminogermanate nanotubes have been successfully synthesized. We have
shown recently, from theoretical calculations, that other imogolite-like
structures can also be, in principle, synthesized.

In our presentation, the results will be presented in the perspective of
the nanomaterials development. Preliminary results about the
functionalization and chemical modification of imogolite will also be
presented.

*Reactivity of the Sulfide Mineral Surfaces – A DFT Study.*



The surface reconstruction[1-3] and the water[4] and ions[5] adsorption on
sulfide minerals are the primary steps for understanding their chemical
stability and the oxidation mechanism in the presence of water and air.
Plane wave/density functional calculations have been performed for
different sulfide minerals such as chalcopyrite (CuFeS2), covellite (CuS)
and arsenopyrite (FeAsS).

Sulfide minerals comprise an important group of minerals in the earth´s
crust and are the main natural source of metals such as copper, zinc,
nickel, lead, gold and silver. Sulfide mineral oxidation in the presence of
water and air forming sulfuric acid, called acid rock drainage (ARD), is a
critical environmental problem near mining regions. ARD is responsible for
acidifying acquifers and mobilizing heavy metals in the environment. The
chalcopyrite leaching for copper extraction from low grade ores is another
technological challenge due to its low kinetics. This process is of great
relevance since 80% of the copper in earth is available as chalcopyrite.

The geometry, band electronic structure, density of states, electron
localization function (ELF) and the Bader´s Quantum Theory of Atoms in
Molecules (QTAIM) analysis are reported. We have shown that the pristine
cleavage of the chalcopyrite in different directions lead to the oxidation
of the sulfide on the surface to form disulfide, S22- and, concomitantly,
the reduction of Fe3+ to Fe2+[3,5,6] Copper and iron atoms, in the first
layer underneath of the surface migrate to form a hydrophobic bidimensional
alloy.

Covellite (CuS), arsenopyrite (FeAsS) and their surfaces have also been
investigated indicating the similarities in the electronic band structure
and the preferential cleavage with respect the chalcopyrite and the most
studied pyrite (FeS2) mineral.
Nota: Los seminarios serán dictados en portugués con la presentación en
inglés.

Invitan: INFAP y Dpto. de Física.
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