Adsorption behavior and mechanism of Mg/Fe layered double hydroxide with Fe3O4-carbon spheres on the removal of Pb(II) and Cu(II).

Mg/Fe layered double hydroxide loaded with Magnetic(Fe3O4) carbon spheres (MCs@Mg/Fe-LDHs) was firstly synthesized by a facile in-situ co-precipitation method to remove Pb(II) and Cu(II) pollution. To search the adsorption mechanism, MCs@Mg/Fe-LDHs was characterized by XRD, FTIR, XPS, TEM, and BET. There may exist surface complexation, precipitation, isomorphic substitution and physical adsorption in MCs@Mg/Fe-LDHs. The combination of those four types of reactions/interactions of metal ions with composite could improve the removal of Pb(II) and Cu(II). And the surface complexation was the main factor leading to the difference maximum adsorption capacity of Pb(II) (3.66 mmol/g) and Cu(II) (5.33 mmol/g). The adsorption kinetics and adsorption thermodynamics of MCs@Mg/Fe-LDHs for Pb(II) and Cu(II) could be better described by pseudo-second-order model and Langmuir model, respectively. The adsorption reaction was a spontaneous and endothermic process. Moreover, there existed competitive effect between Pb(II) and Cu(II) on the co-adsorption by MCs@Mg/Fe-LDHs. And the selectivity adsorption order of MCs@Mg/Fe-LDHs is as follows: Cu(II) > Pb(II) > Zn(II) > Ni(II) > Cd(II). Besides, in the real river water, the MCs@Mg/Fe-LDHs also exhibited stable adsorption capacity for Pb(II). In general, the MCs@Mg/Fe-LDHs has the potential for purification of water contaminated by Pb(II) and Cu(II).