One-pot preparation of a MnO2–graphene–carbon nanotube hybrid material for the removal of methyl orange from aqueous solutions

Abstract

This study presents a MnO₂–graphene–carbon nanotube (MnO₂–G–CNT) hybrid material synthesized in a simple one-pot reaction process by a chemical method. The resulting materials were characterized by different techniques, such as TEM, XRD, FTIR, XPS, and BET surface area measurement. The adsorption behaviors of methyl orange (MO) onto the MnO₂–G–CNT were firstly systematically investigated and experimental results indicated that the material with the highest loading amount of MnO₂ showed an excellent adsorption capacity toward MO. The adsorption kinetics could be well described by the pseudo-second-order model and the Freundlich isotherm model showed a better fit with experimental data than the Langmuir model and the maximum adsorption capacity was determined to be q_max = 476.19 mg g⁻¹. The overall rate process was apparently influenced by intra-particle diffusion and external mass transfer. Moreover, the thermodynamic parameters indicated that the adsorption was spontaneous and exothermic and that the physical adsorption mechanisms included electrostatic interaction, which played a dominant role in the adsorption mechanism between MO and the hybrid material.