Estudo da interação de clusters de Rh com nanoestruturas de carbono via Teoria do Funcional da Densidade

Abstract

Our work consists of the study of the interaction of Rh clusters, from 2 to 15 atoms, with carbon nanostructures (carbon nanotubes and graphene) using first principles calculations, based on the Density Functional Theory. In general, the advantageous combination between carbon nanotubes (CNTs) and transition metal clusters (TMs) is associated with the increase in the chemical reactivity of the CNTs, due to the TM functionalization (naturally CNTs show low reactivity). On the other hand, TM clusters show high reactivity, however, they need a support, since they are obtained in gas phase. In this sense, our work addresses important aspects related to the anchoring of clusters on carbon nanostructures, that is, how the interaction of clusters occurs due to the change in the curvature of carbon structures? The change in curvature occurred through of the choice of three carbon structures: CNT (6,0) (small diameter), CNT (12,0) (medium diameter), and the graphene sheet (infinite diameter). Initially, we performed a study on the Rh bulk, in order to verify if the methodology was in good agreement with the literature. We also focus on the understanding of the main calculation parameters, i.e., convergence tests. Afterwards, we carried out the study of the Rh clusters, from 2 to 15 atoms, in gas phase and the carbon nanostructures, in their pure form. With the understanding of the isolated systems, we proceed to the adsorption step, in order to obtain the atomistic understanding of the Rh clusters adsorption on CNTs. We obtained the lowest energy structures for Rhn, which follow an opened structural pattern (with the formation of cubes). Through the analysis of energetic, structural, electronic, and reactivity properties of clusters and carbon nanostructures, we found an excellent agreement with the literature and great feasibility for the combination between clusters and carbon nanostructures. We found a direct relation between the substrate curvature and the anchoring of the clusters, i.e., we observed an increase (in modulus) in the adsorption energy of the clusters with the increase of the curvature of the carbon structures. In addition, the larger stability of open clusters in relation to the closed ones in gas phase, underwent a reversal when the chemical environment was changed, i.e., when the clusters are deposited in the carbon nanostructures. Both the cluster and the support do not undergo large structural distortions after adsorption. In contrast, the total magnetic moment underwent changes after the adsorption, which is an indication of the cluster adsorption, and also makes these systems promising for applications as nanometric sensors.