Sonochemical synthesis of improved graphene oxide for enhanced adsorption of methylene blue

The adsorption of methylene blue (MB) on graphene oxide (GO) is an interfacial phenomenon influenced by intermolecular interactions between adsorbate and adsorbent's surface. Diversely oxidised GOs were prepared by a modified Tour's method, with the introduction of intermittent ultrasonication steps to enhance oxidation by easing diffusion of the oxidiser. The physicochemical changes were monitored by FTIR, XRD, TGA, nitrogen gas adsorption, UV-Vis, Raman, XPS, SEM and zeta potential. All results corroborate well to evidence the im-provements achieved: beside halving process time, the ultrasonication steps generated higher concentrations of carboxylic groups and created mesoporosity in the final materials. The adsorption capacities of the GOs were assessed by MB uptakes as a function of pH, time, and adsorbate concentrations, and equilibrium data were fitted with classical isotherm models, along with pseudo-first-order, pseudo-second order, and Elovich kinetic models. The adsorption capacities, 2294 mg/g at pH 7, and 2301 mg/g at pH 12, are among the highest reported. Comparative analyses of the materials before and after adsorption suggest that MB removal relies on multiple factors: porosity of the material, electrostatic attractions, hydrogen bonding, and 7C-7C interactions. Moreover, the most performant GO was highly regenerable, maintaining a removal efficiency > 90% after 5 cycles.

Automated summary

The adsorption of methylene blue on graphene oxide is influenced by intermolecular interactions and the physicochemical changes of GO. The modified oxidation method enhanced the adsorption capacities and created mesoporosity in the final materials. Moreover, the most performant GO showed high regenerability and maintained a removal efficiency greater than 90% after multiple cycles.