Competitive adsorption of Cu2+, Cd2+ and Ni2+ from an aqueous solution on graphene oxide membranes

A novel graphene oxide membrane (GOM) was prepared using the vacuum filtration-induced directional flow method. The properties of GOM were characterized by scanning electron microscope, X-ray diffraction instrument, transmission electron microscope, and Fourier transform infrared spectroscopy apparatus. The adsorptive properties of Cu 2+ , Cd 2+ and Ni 2+ onto GOM were systematically investigated in single, binary and ternary solutions by batch experiments. In a single system, the maximum adsorption capacities of Cu 2+ , Cd 2+ and Ni 2+ obtained by the Langmuir model were 1.21, 0.81 and 1.08   mmol/g, respectively. The isotherms results for Cu 2+ indicated that GOM exhibited good selectivity in the adsorption of Cu 2+ over Cd 2+ and Ni 2+ . The adsorption capacity followed the order of Cu 2+   >   Ni 2+   >   Cd 2+ in binary systems. For ternary system, the order of the adsorption capacity was Cu 2+   >   Cd 2+   >   Ni 2+ . Previously adsorbed metal ions on GOM could be displaced by subsequently adsorbed metal ions from the solution. The difference in hard and soft acids and bases of Cu 2+ , Cd 2+ and Ni 2+ solutions was identified as the main reason for GOM to be able to selectively adsorb favorable metal ions during competitive adsorption in binary systems. This interaction mechanism between the favorable component and other metal ions could be the primary cause of direct displacement.