Preparation of polyethylene polyamine@tannic acid encapsulated MgAl-layered double hydroxide for the efficient removal of copper (II) ions from aqueous solution

The MgAl-layered double hydroxide (LDH) was modified with polyethylene polyamine (PP) and tannic acid (TA) to improve the adsorption property of heavy metal ions. The PP@TA encapsulated LDH (denoted as LDH-PP@TA) was prepared via the combination of catechol chemistry and Michael addition and/or Schiff base reaction and characterized through TEM, FT-IR, SEM, TGA, and XPS. The adsorption performance was investigated by using LDH-PP@TA as adsorbent to adsorb the copper (II) ions from aqueous solution. The effect of contact time, solution pH, initial copper (II) ions concentration and temperature were investigated. The LDH-PP@TA exhibited high adsorption capacity of 41.56 mg/g, which is almost double that by LDH (23.39 mg/g). Equilibrium data for adsorption of copper (II) ions on adsorbents could be well fitted by the pseudo-second-order and Langmuir equations. Thermodynamic studies show the adsorption process is spontaneous and endothermic. Electrostatic adhesion and formation of copper complex are the major mechanisms for the copper (II) ions removal by LDH-PP@TA. These results reveal the great potential of LDH-PP@TA in the application of heavy metal ions removal.