Adsorption mechanism of copper and lead ions onto graphene nanosheet/δ-MnO2

The removal behaviors of Cu(II) and Pb(II) ions onto graphene nanosheet/δ-MnO2 (GNS/MnO2) adsorbent were investigated under various conditions including contact time and initial metal concentrations. The surface interactions involved in the adsorption process and the regeneration were also explored. The equilibrium adsorption data could be well described by the pseudo-second-order kinetic model and the Langmuir equation. Weber–Morris model suggested that the sorption was a multi-step with the pore and surface diffusion process. The maximum adsorption capacity of GNS/MnO2 for Cu(II) and Pb(II) ions were 1620 and 781 μmol g−1, respectively. FTIR and XPS studies illuminated that the formation of complexes on GNS/MnO2 surface mainly consisted of the oxygen in hydroxyl (C–OH, Mn–OH) and carboxyl groups. Moreover, XRD analysis further confirmed that Cu(II) or Pb(II) could not only adsorb on the surface of GNS/MnO2, but also intercalate the layered of MnO2. GNS/MnO2 can be used four times by HCl solution.