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.

Automated summary

The eco-friendly PASP/LDH intercalation compound was synthesized and used for the removal of heavy metal ions from aqueous solutions. The compound exhibited high adsorption capacity and selectivity, with chemisorption as the main adsorption process. The excellent adsorption properties were attributed to the inner-sphere complexation between the compound and heavy metal ions.