Estudo da interação da benzonitrila com nanoestruturas de carbono (grafeno, nanotubos e fulerenos)

Abstract

In this work, we have performed ab initio calculations of the interaction of benzonitrile molecule, a typical Lewis base, with some carbon nanostructures such as Single Wall Carbon Nanotubes (SWNTs), Graphene and Fullerenes. We also have chemically modified these carbon nanostructures by doping with transition metals (Fe). Structural modifications such as vacancies were also investigated in order to improve the interaction. The behavior of interacting systems at electronic level was studied after structural relaxation. The ab initio calculations are based on Density Functional Theory (DFT) implemented in the SIESTA code which is very efficient for this purpose. It performs fully self-consistent calculations solving Kohn-Sham (KS) equations, adding for the exchange and correlation term the generalized gradient approximation (GGA) or local density approximation (LDA). Our calculations predicted that benzonitrile molecule weakly interacts with pristine SWNTs. There is a slightly increasing in the interaction energies when the axis molecule is parallel to the tube axis and the aromatic ring of benzonitrile is on tube surface. This suggests that π − π interaction is stronger than π-CN interaction. This behavior is also observed when we modified the tubes with a single atom defect since the adsorption energies values are not modified. The latter result suggests that this defect does not improve the interaction of benzonitrile with SWNTs. The adsorption of benzonitrile molecule on a graphitic layer (graphene) revealed that graphene can interact more strongly than SWNTs via π − π stacking. Our results for pristine fullerenes are similar to prisitne SWNTs. The interaction can be significantly improved when a transition metal (Fe) intermediates the interaction between these carbon structures (SWNTs and fullerenes) with benzonitrile. In this adsorption process are observed: a strong rehybridization of orbitals, a considerable charge transfer between the systems, an increasing in binding energies values and significant modifications in the density of electronic states. Our calculations were confirmed by means experiments perfomed SWNTs and C60 in benzonitrile solutions. The spectroscopy analysis (IR, Raman, Absorption and Emission) revealed that benzonitrile interacts weakly with purified SWNTs. Nonpurified SWNTs were submitted to interaction with benzonitrile and some modifications were observed in absorption and Raman sprectra. After purification process, the purified nanotubes did not interact strongly with benzonitrile. Experimental observations revealed no significant shifts in the RBM, D-band and G-band peaks of SWNTs. These results and TEM images of solutions suggest that benzonitrile interacts more strongly with impurities (other amorphous carbonaceous materials, nanoparticles, catalyst particles, etc.). We suggest that catalyst particles (such as Fe) can play a fundamental role in carbon nanotubes functionalization studies.