Efficient removal of Pb(II) and Hg(II) with eco-friendly polyaspartic acid/layered double hydroxide by host-guest interaction

The eco-friendly polyaspartic acid/layered double hydroxide (PASP/LDH) intercalation compound was synthesized and applied for the removal of heavy metal ions from aqueous solutions. The maximum adsorption capacities were 229.2 mg/g and 208.6 mg/g for the adsorption of Pb2+ and Hg2+ ions, respectively. Further, the PASP/LDH displayed high adsorption selectivity (Pb2+ > Hg2+ > Cd2+ > Ni2+ > Cu2+ > Zn2+). The effects of contact time, ions concentrations, pH and coexisting ions on the removal of metal ions were investigated. The adsorption kinetics followed the pseudo-second-order kinetic model, which indicated that the adsorption processes were chemisorption. The adsorption isotherms were agreed with Langmuir model. The excellent adsorption properties mainly originated from inner-sphere complexation between -COO- groups on the surface of LDH and heavy metal ions. DFT calculations and the experimental results revealed that the host-guest interaction would enhance adsorption capacity of PASP/LDH though the change of surface charge and wettability of LDH laminate.