Preparation of 3D graphene-carbon nanotube-magnetic hybrid aerogels for dye adsorption

Novel hybrid aerogels were prepared by adding ZnCl₂, NiCl₂·6H₂O, FeCl₂·4H₂O and FeCl₃·6H₂O to a suspension of equal weights of graphene oxide and oxidized carbon nanotubes, followed by co-precipitation under basic conditions. The aerogels were then crosslinked with polyvinyl alcohol in water and freeze-dried. They consisted of magnetic Ni_0.5Zn_0.5Fe₂O₄ nanoparticles, graphene oxide, carbon nanotubes and polyvinyl alcohol, which have active sites that attract dye molecules and could be extracted from water by applying a magnetic field. Using optimum mass ratios of ZnCl₂/NiCl₂·6H₂O/FeCl₂·4H₂O/FeCl₃·6H₂O/(graphene oxide+oxidized carbon nanotube) at 6∶6∶12∶12∶1, the hybrid aerogel has a high adsorption capacity of 71.03 mg g⁻¹ for methylene blue and a moderate magnetic strength of M_S = 3.519 emu g⁻¹. Its removal efficiencies for methylene blue, methyl orange, crystal violet and a mixture of equal masses of the three were 70.1%, 4.2%, 8.9% and 11.1%, respectively for the same dye concentration of 0.025 mg mL⁻¹. It could be used for 3 regeneration cycles with a regeneration efficiency of over 82%. It was also not toxic to the living organisms, suggesting that it is a promising adsorbent for treating industrial wastewater.