Efficient removal of organic dyes using a three-dimensional graphene aerogel with excellent recycling stability

The development of a renewable absorbent with a high adsorption efficiency is of great importance for the purification of dye wastewater. A nitrogen-doped graphene aerogel (N-GA) was prepared by a one-step hydrothermal and freeze-drying method using polyvinyl alcohol (PVA) as a cross-linking agent. Results indicated that the nitrogen doping provided more adsorption sites for the dyes. The PVA-N-GA showed excellent adsorption efficiencies for methylene blue (MB) (98.39% at pH=8) and methyl orange (MO) (78.78% at pH=2). The adsorption kinetic data of MB and MO on the PVA-N-GA were better fitted with a pseudo-second-order kinetic model than a pseudo-first-order kinetic model while the adsorption isotherms of MB and MO were better described by the monolayer Langmuir model and the multilayer Freundlich model, respectively. The PVA-N-GA showed excellent recycling stability with a negligible decay of adsorption efficiency after five cycles, which was ascribed to PVA making the three-dimensional (3D) pore structure of the N-GA more stable. The adsorption of the PVA-N-GA for dyes was mainly attributed to the pi-pi bonds, hydrogen bonds and electrostatic interactions.