Adsorption kinetics, isotherms and mechanisms of Cd(II), Pb(II), Co(II) and Ni(II) by a modified magnetic polyacrylamide microcomposite adsorbent

• A magnetic hydroxamic acid modified polyacrylamide/Fe3O4 adsorbent was prepared.
• The prepared adsorbent is effective and recyclable for heavy metals.
• Adsorption fit well with pseudo-second order model and Sips isotherm model.
• Pb(II) could be preferentially adsorbed from multi-metal systems.
• The adsorption mechanism was validated by FTIR measurement and DFT calculation.

A novel magnetic hydroxamic acid modified polyacrylamide/Fe3O4 adsorbent (M-PAM-HA) was prepared with acrylamide by microemulsion polymerization and then nucleophilic substitution of hydroxamic acid. The morphology, structure of the magnetic adsorbents before (M-PAM) and after modification (M-PAM-HA) were characterized and their adsorption properties for the removal of metal ions by varying test conditions were also investigated. The modified M-PAM exhibited lower swelling property and less magnetic leaching than M-PAM. Their adsorption kinetics followed the pseudo-second order model. The maximum adsorption capacities of metal ions ranged from 0.11 to 0.29 mmol g−1 for M-PAM and 0.88–1.93 mmol g−1 for M-PAM-HA, respectively. Sips model fitting well to experimental data revealed the surface heterogeneity of the prepared adsorbents. In multi-metal systems, M-PAM-HA showed the relative selectivity toward Pb(II), although Pb(II) was adsorbed the least in their corresponding one-metal systems. The adsorption mechanism was proposed based on the results of FTIR and density functional theory (DFT) calculation.

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