Fractional distribution of graphene oxide and its potential as an efficient and reusable solid catalyst for esterification reactions

Graphene oxide (GrO) prepared by the Hummers method was separated into three different fractions (GrO(5000), GrO(2000), and GrO(res)) on the basis of their dispersion stability in the water. Infrared, nuclear magnetic resonance, X-ray photoelectron spectroscopy, and elemental analyses revealed that GrO(5000) possesses a high degree of oxygen functionalities including phenolic, carboxylic, and -OSO2H groups, compared with the other fractions. The GrO(5000) was found to be a highly efficient and reusable solid catalyst for the esterification of various carboxylic acids with a variety of alcohols to furnish corresponding esters in high to excellent yields. The catalytic activity of the GrO(5000) was attributed to the ability of highly polar GrO(5000) scaffold to adsorb/attract reactants, where the acid functionalities of GrO(5000) facilitated the esterification process efficiently. The chemical and structural features of GrO(5000) were discussed to understand the improved catalytic activity compared with GrO(2000) and conventional solid acid catalysts. Copyright (c) 2014 John Wiley & Sons, Ltd.