Adsorption capacity comparison between graphene oxide and graphene nanoplatelets for the removal of coloured textile dyes from wastewater

The synthesis of graphene oxide (GO) nanosheets, to be used as an adsorbent for the removal of textile dyes from wastewater, was optimized by the modified Hummers method. The GO nanosheets produced were compared with commercial graphene and characterized by X-ray diffractometry (XRD), Raman spectroscopy, specific surface area analysis, and zero-charge point (pHpcz). Both GO and graphene nanomaterials were originally used to adsorb two coloured dyes (direct red 81 and Indosol SFGL direct blue), which are commonly disposed in textile industrial effluents. Adsorptive assays were performed to determine and compare the variables that most influence the process, such as pH and dye concentration. The mechanisms of adsorption are proposed based on the strong interactions between the graphene oxide (due to its high functionalization with hydroxyl and carboxylic groups) and the active functional groups of the dyes (according to its colour) that, in general, overcome the weaker electrostatic forces between water/commercial graphene/dye systems.