Hydrothermal synthesis of a graphene/magnetite/montmorillonite nanocomposite and its ultrasonically assisted methylene blue adsorption

A graphene/magnetite/montmorillonite nanocomposite (GQDs/Fe3O4/MMT) was synthesized via a simple green hydrothermal method. The effects of pH, temperature, contact time, adsorbent quality, dye concentration and ultrasonication on the adsorption performance of methylene blue (MB) were investigated. For ultrasonic-assisted adsorption, the adsorption rate of GQDs/Fe3O4/MMT can reach 10 s. Ultrasound strongly affected the adsorption equilibrium time but did not affect the maximum adsorption capacity. The main reason for ultrasonic-assisted dyes ultrafast adsorption is cavitation that graphene quantum dots (GQDs) promote nucleation. By adjusting the amount of surface charge, the adsorbent has excellent selective ultrasonic-assisted ultrafast adsorption properties of mixed dyes. The adsorption performance of the GQDs/Fe3O4/MMT was weakly affected by temperature. The theoretical and experimental maximum adsorption capacities were 429.4 mg/g and 225.0 mg/g, respectively. The adsorption kinetics and adsorption isotherms agree well with the pseudo-second-order equation and the Langmuir equation, respectively. After six adsorption/desorption cycles, the adsorption and desorption efficiency of the dye decreased slightly. The results indicated that the GQDs/Fe3O4/MMT nanosorbent has strong potential for removing the cationic dye MB from wastewater.