Adsorption of methylene blue in water by reduced graphene oxide: Effect of functional groups

Here we prepared three reduced graphene oxides-hydrazine and H-2/Ar reduced graphene oxide at 200 and 500 degrees C (RGO-N, RGO-H-200 and RGO-H-500) with almost identical Brunauer-Emmett-Teller (BET) surface areas to study the effect of functional groups on adsorption behaviors for the removal of methylene blue (MB) from aqueous solution. The maximum adsorption capacities of RGO-N, RGO-H-200 and RGO-H-500 for MB were 159, 91 and 81 mg/g at 283 K, respectively. X-ray photoelectron spectra measurements demonstrated that the content of relevant functional groups in three adsorbents differs from each other. The C=O or C=N double bonds are able to couple with the C-C/C=C bonds to form a large conjugate structure, enhancing the interactions between RGO and MB molecules. While, the C-OH bonds contribute little, if any, to the increase of adsorption efficiency because of the steric hindrance towards benzene-ring containing dye molecules.