Tesis
Adsorção de cluster de ouro em materiais bidimensionais
Fecha
2017-07-31Autor
Cardoso, Günther Luft
Institución
Resumen
In this work, we studied the interaction of Au34 gold cluster with different two-dimensional
materials. Au clusters, differently of their macroscopic form, are chemically reactive. Their
use requires substrates. The two-dimensional materials chosen as substrates were graphene,
tungsten diselenide and boron nitride. Besides this, we studied the interaction of Au34 cluster
with defective graphene (vacancy) and tiophenol functionalized graphene. These materials
were chosen due the differences among their physical properties, and the facility one
can obtain monolayers out of these materials. The tiophenol functionalized graphene were
utilized because it is experimentally verified that this material is a good catalyst, and it is
efficient to anchor gold clusters, avoiding them to agglomerate in aggregates with lower
surface/volume ratio, fact that diminishes the efficiency of chemical reactions that needs
catalysts. The gold cluster chosen possess 34 atoms because this is one of the magical
numbers for cluster of this element. The most stable configuration for this gold cluster
has C3 symmetry, with diameter around of 0.8 nm. All calculations were performed using
the density functional theory with the gradient generalized approximation for the exchange
and correlation functional, as implemented in the code VASP. We determined the bond
energies, structural distortions and charge exchange between the interacting systems and
analyzed the electronic structures through their density of states. Our results indicates that
the gold cluster practically don’t interact with the graphene and boron nitride sheets. The interactions
of cluster with tiophenol funcionalized graphene and tungsten diselenide showed
higher bond energies, while the interactions with defective graphene showed intermediate
bond energy. The active sites for electrophilic and nucleophilic reactions are localized in
the gold atoms, with active sites in the substrate being inactive due steric hindrance. The
chemically active systems, with the gold clusters attached in the substrate and amphoteric
behavior presents different values of energy gap, allowing their use in different chemical
environments.