No abstract

A ball-milling treatment can be employed to exfoliate graphite through interactions with commercially available melamine under solid conditions. This procedure allows the fast production of relatively large quantities of material with a low presence of defects. The milling treatment can be modulated in order to achieve graphene flakes with different sizes. Once prepared, the graphene samples can be redispersed in organic solvents, water, or culture media, forming stable dispersions that can be used for multiple purposes. In the present work, we have screened electron-rich benzene derivatives along with triazine derivatives in their respective ability to exfoliate graphite. The results suggest that the formation of a hydrogen-bonding network is important for the formation of multipoint interactions with the surfaces of graphene, which can be used for the exfoliation of graphite and the stabilization of graphene in different solvents. Aminotriazine systems were found to be the best partners in the preparation and stabilization of graphene layers in different solvents, while the equivalent benzene derivatives did not show comparable exfoliation ability. Computational studies have also been performed to rationalize the experimental results. The results provide also the basis for further work in the preparation of noncovalently modified graphene, where derivatives of aminotriazines can be designed to form extensive hydrogen-bond 2D networks on the graphene surface with the aim of manipulating their electronic and chemical properties.

Several [3 + 2] thermal cycloadditions between azomethine ylides and nitroalkenes have been studied both theoretically and experimentally. When the N-metalated 1,3-dipoles are used, the reaction is stepwise. The corresponding zwitterionic intermediates have been located computationally and observed by NMR monitoring. In the case of N-unsubstituted azomethine ylides, the reaction can be concerted or stepwise, depending upon the ability of the substituents to stabilize zwitterionic intermediates. A general model is proposed to explain the observed phenomena. This simple model can be extended to other thermal cycloadditions to predict the stepwise or concerted nature of their mechanisms without computing complete reaction coordinates.

Despite the great success of Microwave Assisted Organic Synthesis (MAOS) there is still a lack of knowledge about the interaction of the electromagnetic radiation with matter. In consequence, it has been very difficult to rationalize the effect of microwave irradiation in chemistry, to determine the existence of microwave effects (thermal and non-thermal) and to develop predictive models on the characteristics required for a reaction to be improved under microwaves. This has been a handicap to develop new chemistry under microwave irradiation and the origin of many controversies. This personal account collects some new findings in this field and our work on the use of computational chemistry to develop predictive models and to determine parameters related to thermal and non-thermal effects, with clear advantages over experimental methods where separation of these effect is almost impossible.

In this work, CNTs have been bombarded with low energy N ions. X-ray photoelectron spectroscopy have been used to determine the binding configuration of the N-doped CNTs. AFM was also used to determine their morphology and mechanical properties. The same morphology is maintained after the N 2 + bombardment. XPS analysis shows that the N 1s core level spectra for N-doped CNTs can be deconvoluted in terms of two peaks related to sp 2 (C -N=C) and sp 3 hybridization (C -N configuration). This interpretation is in concordance with the increase of the hardness observed by AFM nanoindentations when the sp 3 contributions increase.