RESUMO

CO2 is the most abundant greenhouse gas, and for this reason, it is the main target for finding solutions to climatic change. A strategy of environmental remediation is the transformation of CO2 to an aggregated value product to generate a carbon-neutral cycle. CO2 reduction is a great challenge because of the large C=O dissociation energy, ~179 kcal/mol. Heterogeneous photocatalysis is a strategy to address this issue, where the adsorption process is the fundamental step. The focus of this work is the role of adsorption in CO2 reduction by means of modeling the CO2 adsorption in rutile metallic oxides (TiO2, GeO2, SnO2, IrO2 and PbO2) using Density Functional Theory (DFT) and periodic DFT methods. The comparison of adsorption on different metal oxides forming the same type of crystal structure allowed us to observe the influence of the metal in the adsorption process. In the same way, we performed a comparison of the adsorption capability between two different surface planes, (001) and (110). Two CO2 configurations were observed, linear and folded: the folded conformations were observed in TiO2, GeO2 and SnO2, while the linear conformations were present in IrO2 and PbO2. The largest adsorption efficiency was displayed by the (001) surface planes. The CO2 linear and folded configurations were related to the interaction of the oxygen on the metallic surface with the adsorbate carbon, and the linear conformations were associated with the physisorption and folded configurations with chemisorption. TiO2 was the material with the best performance for CO2 interactions during the adsorption.

Assuntos

Dióxido de Carbono , Óxidos , Dióxido de Carbono/química , Adsorção , Óxidos/química , Carbono , Catálise

RESUMO

In solution, the solvent determines the molecular conformation and the chemical reaction viability and selectivity. When solvent-solute and solvent-solvent interactions present similar strengths, explicit salvation is the best way to describe a system. The problem to solve is how big the explicit shell should be. In this paper, we want to answer one of the fundamental questions in the implementation of explicit solvation, exactly how many solvent molecules should be added and where they should be placed. Here we determine the first solvent sphere around a molecule and describe how it controls the conformation and selectivity of a selected reaction. NMR experiments were carried out to identify the number of solvent molecules around the solute that constitutes the first solvent sphere, and the interaction between this solvent sphere and the solute was detected using DFT and QTAIM calculations. A new approach to the solvation energy is presented. Finally, we established the role of solvent molecules in the conformation of the solute and in the transition states that produce the two possible products of the reaction.

RESUMO

Four Metal-Organic Frameworks (MOFs) were modeled (IRMOF-C-BF2, IRMOF-C-(2)-BF2, IRMOF-C'-BF2, and IRMOF-C-CH2BF2) based on IRMOF-1. A series of linkers, based on Frustrated Lewis Pairs and coumarin moieties, were attached to IRMOF-1 to obtain MOFs with photocatalytic properties. Four different linkers were used: (a) a BF2 attached to a coumarin moiety at position 3, (b) two BF2 attached to a coumarin moiety in positions 3 and 7, (c) a BF2 attached in the coumarin moiety at position 7, and (d) a CH2BF2 attached at position 3. An analysis of the adsorption properties of H2, CO2, H2O and possible CO2 photocatalytic capabilities was performed by means of computational modeling using Density Functional Theory (DFT), Time-Dependent Density Functional (TD-DFT) methods, and periodic quantum chemical wave function approach. The results show that the proposed linkers are good enough to improve the CO2 adsorption, to hold better bulk properties, and obtain satisfactory optical properties in comparison with IRMOF-1 by itself.