Estudo da interação de átomos metálicos com materiais bidimensionais via teoria do funcional da densidade

Abstract

In this master’s thesis we report a theoretical study on the interaction of transition metal atoms (TM = Co, Ni, Rh, Pd, Ir and Pt) with two-dimensional materials (2D) based on graphene, using graphene (pristine - GP and with monovacancy - GMV) and hexagonal boron nitride (h-BN) via Density Functional Theory (DFT). The set of TMs that determined theoretical indicators for the best candidates for single-atom catalysts (SACs) were considered, constituting a sampling of the three transition metal series of groups 8 and 9 of the periodic table, which are part of a select group highly used in theoretical and experimental studies, with numerous applications, due to the unfilled d layer. In the first stage of the study, we calculated the main properties of the substrates and TMs separately, which agreed with the literature and served to confirm the methodology adopted. By removing a carbon atom from the GP, we obtained a more reactive support (GMV) while the structural part remained minimally altered. The Co/GP, Co/h-BN and Co/GMV systems ensured an initial characterization of the substrates and adsorption trends of the metal atom on each substrate, such as the choice of a substrate size of 6x6x1 unit cells. We found that GP-adsorbed TMs with higher (lower) d-state occupation have bridge (hollow) site-preference that exhibit a more reactive character. This is the case for the more stable systems Co/GP, Ni/GP and Rh/GP having adsorption at the hollow site and Pd/GP, Ir/GP and Pt/GP at the bridge site. The adsorption preference for the top site over nitrogen (N) of the h-BN substrate is attributed to the fact that the p orbitals perpendicular to the plane are empty in boron (B) and occupied by two electrons in N. In the case of the GMV substrate, the TMs satisfy the missing bonds of the missing graphene carbon (C) atom and enter into the vacancy. The total magnetic moment of the three substrates had a similar behavior, where we identified the relationship with the filling of the d states, being non-null (null) for those TMs with lower (higher) occupancy. The energetic and structural properties of the more stable systems considering TMs/GP and TMs/h-BN showed strong interaction, in terms of adsorption and distortion energies for applications in SACs when rhodium (Rh) is adsorbed. In the incorporation of TMs in GMV, the interaction is more easily established for iridium (Ir) and Rh at the same time that it loses more stability. The greater interaction accompanied by the higher magnitude of adsorption energy and loss of stability is associated with the GMV substrate being more reactive. In all these systems the supports did not suffer significant structural distortions. The electronic properties experienced stability of substrates due to adsorption and that in TMs/GP, TMs/h-BN and TMs/GMV systems, Rh is within the group of TMs that exhibited the lowest decrease in binding states. The greater charge transfer and orbital hybridization confirm GMV as the best substrate for SAC applications.