Adsorção de cluster de ouro em materiais bidimensionais

• Ano de defesa: 2017
• Autor(a) principal: Cardoso, Günther Luft
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Santa Maria; Brasil; Física; UFSM; Programa de Pós-Graduação em Física; Centro de Ciências Naturais e Exatas
• Palavras-chave em Português: Cluster; Materiais bidimensionais; Energia de ligação; Catálise; Bidimensional material; Bond energy; Catalysis; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: http://repositorio.ufsm.br/handle/1/13929

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.