Enhanced adsorption of methylene blue on chemically modified graphene nanoplatelets thanks to favorable interactions

In the present study, the used graphene nanoplatelets (GNPs) are of high structural quality offering the opportunity to modify the adsorbent/adsorbate interactions. Their chemical modification by simple acid oxidation leads to their facile dispersion in water. Morphological, structural, and chemical properties of the functionalized GNPs are deeply investigated by a set of complementary characterization techniques. The parametric investigation including effects of initial concentration, contact time, solution pH, and temperature of methylene blue (MB) adsorption allows to identify those being relevant for MB removal enhancement. MB adsorption is found to increase with contact time, solution temperature, and acidic pH. The nature of the MB-GNP interactions and the possible adsorption mechanisms, relatively little understood, are here particularly studied. MB-GNP adsorption is shown to follow a Langmuir isotherm and a pseudo-first-order kinetic model. The adsorption capacity of MB on the chemically modified GNPs (qm = 225 mg/g) with respect to the external surface is relatively high compared to other carbon nanomaterials. Such adsorbent certainly merits further consideration for removal of other dyes and heavy metals from wastewaters.