• DFT
• Diels-Alder Cycloaddition
• Graphene Functionalization
• Reduced Graphene Oxides

Graphene Oxide (GO) and its reduced form (rGO), obtained from the chemical exfoliation of graphite, are currently becoming particularly important to the progress in graphene technology thanks to the scalability of their production process.
Exfoliation in a strongly oxidating environment causes the formation of defects and the inclusion of oxygen containing functional groups in the structure, mostly hydroxy and epoxy but carbonyl and carboxylic are also found on the borders, leading to the disruption of the crystalline lattice. The oxidation can be reversed by a reduction process to obtain rGO partly restoring the structure: most of the functional groups are removed but the defects will grow in number. The final products also gain better dispersibility in polar solvents with respect to pristine graphene and a band gap, opening to interesting possibilities in nanoscale applications.
Previous studies on the oxoreduced structures, both theoretical and experimental, also proved increased reactivity towards the Diels-Alder Cyclo-addition (DA), a single step reaction which can be carried out in mild conditions without the need for a catalyst, adding new possibilities for the functionalization of graphene. The DA consists in the sharing of the double bonds between a diene and a dienophile to form a cyclic product: graphene can act both as a diene or dienophile, but it is found to be more prone to covalent bonding only on borders and defects while noncovalent complexation is favored on pristine sites.
Density Functional Theory (DFT) is a first-principles quantum chemistry method widely used to study molecular structures and energetic parameters difficultly accessible in experimental environment. In the present work the reactivity of several Graphene models, representing different oxidation and reduction states, with N-Methyl Maleimide (Maleimide), an attractive molecule as it opens the possibility to functionalize graphene with polymers in nanostructured applications, was studied through DFT. The aim is to obtain a good understanding of the reactivity in the dependence of the different oxidation state, binding site, solvent and Temperature effects also including kinetic calculations for the estimation of the reaction rates from the activation energies. The results show how the covalent functionalization is highly favorable on border, defective and oxidated sites while the non-covalent complexation is preferred on pristine structures coherently with previous findings for the graphene DA.
 
In the present work the reactivity of different Graphene sheets with Maleimide was studied using First Principles Methods to model the reactivity of differently oxidated and reduced graphene nanoribbons. The Thermochemical results confirm that covalent binding is highly favored by the presence of defects and oxygen-containing groups leading to stable products and relatively small activation barriers.
New valuable information for the experimental framework was found in studying the solvation effects indicating how the rates of reaction are significantly higher in solvent even if the impact on the activation energy is small, due to exponential dependence on the barrier, while the non-covalent complexation is hindered by the presence of the solvent also favoring covalent bonding. Different reactant molecules were tested to find that Maleimide is more reactive to GO and rGO then the already widely characterized Maleic Anhydride. Maleimide is capable of being bound to polymeric residuals opening to large scale applications in graphene functionalization and polymer nanocomposites realization through the DA of GOs and rGOs.
A possibility to extend the knowledge on the realization of graphene functionalized polymeric nanocomposites can be found in the formulation of a multi scale description of the systems, starting from the quantum-chemical models the to develop a Reactive Molecular Dynamics Force Field (ReaxFF) allowing for the dynamical simulation of the systems, hence the study of kinetic and structural properties on larger scales.