Reatividade química da superfície da calcopirita e mecanismo de separação da mistura etanol-água em metal-organic frameworks

Abstract

The description of the chemical reactivity in the solid/liquid interface is a challenge for computational simulation and molecular modelling. In this thesis, two chemical processes in the solid/liquid interface, which are important from the scientific and technological point of view, were investigated: the reactivity of chalcopyrite and the water/ethanol separation in a metal>organic framework (MOF). Chalcopyrite is an iron and copper sulphide (CuFeS2), which is very important, because is the main source of copper in the world. Its slow leaching kinetic intrigues researchers, who spend efforts for understanding the molecular mechanism related to this process. The first step of this process was investigated consisting the surface reconstruction and its interaction with water and ions present in the leaching solution. Sulphur terminated surfaces reconstruct forming disulphide (S22>), while metal terminated surfaces reconstruct forming a bidimensional alloy>like structure. Water molecules adsorb on chalcopyrite surface bonding covalently to iron atoms. Similarly, HCl and different chemical species of H2SO4 adsorb on the iron sites of the reconstructed surfaces by a covalent bond. The impact of these results in the understanding of the reaction mechanisms was discussed in details. The separation mechanism of the ethanol/water mixture in the MOF Zn2(BDC)2(TED) [BDC: benzene>1,4>dicarboxilate, TED: triethylenediamine) was also investigated in this thesis. This material could be used in the ethanol production, having important impact in the whole Brazilian energetic program. The modelling of this system, however, is limited by several theoretical difficulties such as the description of weak intermolecular interactions and the choice of appropriate chemical models. DFT calculations combined with a periodic model allowed us to identify the separation mechanism of the mixture components. The combination of hydrophilic and hydrophobic sites geometrically close explains the material selectivity for ethanol than water due to the combination of hydrogen bonds and van der Waals interaction of the carbon chain of alcohol. The reasoning of the experimental results