Grafenos preparados por métodos químicoscaracterísticas y aplicaciones

Resumen

[EN] The main goal of the present work is the development of techniques for the preparation of graphene that can be used effectively and safely on a large scale. Currently, one of the most promising techniques is based on the exfoliation of graphite oxide to graphene oxide and its subsequent reduction. In this work, effective and safe alternatives to the commonly used but hazardous hydrazine as a reducing agent of the graphene oxide are investigated. In particular a range of natural antioxidants were tested including vitamins, amino acids and organic acids, as potential reducing agents of graphene oxide. Nine novel reducing agents were identified; some of them, e.g. vitamin C appeared as potential substitutes for hydrazine. To make sure that aqueous dispersions of chemically reduced graphene oxide sheets are colloidally stable, it is necessary to keep these dispersions within a strict range of physicochemical conditions (pH, sheet concentration, electrolyte concentration, etc.), and under different conditions a dispersing agent should be used to stabilize the sheets. In this work, a comparative study was made towards the use of a wide range of surfactants in the stabilization of reduced graphene oxide under non optimal physicochemical conditions. It was observed that the efficacy of the surfactants depends on the specific characteristics of the surfactant and its concentration, and the specific conditions of the colloidal environment determine the most suitable surfactants in each case. Another method for the preparation of graphene investigated here was the direct exfoliation of the pristine graphite in water induced by ultrasound, which strictly requires the use of stabilizers. A comparative study regarding the capacity and the efficacy of different ionic and non-ionic surfactants was carried out to this effect. The conclusion was that, in general, non-ionic surfactants were more effective than their ionic counterparts towards exfoliation and stabilisation of high concentrations of structurally perfect graphene. Finally, several hybrid materials made up of graphene and either metallic nanoparticles or mesoporous silica nanoparticles, with potential use in several applications were prepared and characterized. In particular, it was demonstrated that certain graphene-silver nanoparticle hybrids possess an excellent catalytic activity for the reduction of 4-nitrophenol with sodium borohydride.