Enhanced adsorption performance, separation, and recyclability of magnetic core-shell Fe3O4@PGMA-g-TETA-CSSNa microspheres for heavy metal removal

A novel magnetic core-shell chelating adsorbent of Fe3O4@polyglyceryl methacrylate-graft-triethylenetetramine-CSSNa (Fe3O4@PGMA-g-TETA-CSSNa) was fabricated via polymerization-grafting-adhesion-crosslinking- modification using Fe3O4 microspheres as core and polyglyceryl methacrylate-graft-triethylenetetraminedithiocarbamate sodium as functional layer. The process was conducted to enhance the rapid and efficient removal of heavy metal ions in aqueous solution and facilitate the separation, recovery, and recyclability of adsorbents. The as-obtained Fe3O4@PGMA-g-TETA-CSSNa microspheres were composed of an approximately 500 nm magnetic core and approximately 35 nm of uniform gray functional layers. The -CSS- content and measured magnetic saturation value (Ms) of Fe3O4@PGMA-g-TETA-CSSNa microsphere were 1.6747 mmol/g and 48.92 emu/g, respectively. The as-obtained adsorbent exhibited highly efficient and rapid adsorption for Pb2+ and Cd2+ in the pH range of 4.00-8.00. Adsorption followed the Langmuir and pseudo-second-order models. The adsorption capacities for Pb2+ and Cd2+ were 229.41 and 210.65 mg/g at 293 K in the Langmuir model, respectively, and adsorption equilibrium was reached within 10 min. Adsorption was a spontaneous endothermic process featuring an entropy increase with adsorption activation energies of 31.6924 kJ/mol for Pb2+ and 16.8445 kJ/mol for Cd2+, involving electrostatic attraction, physisorption, and chemisorption. S, N, and O in the active layer of the resulting adsorbent were all involved in the formation of coordination bonds. They particularly formed a symmetrical S-coordinated four-membered ring of (-CSS-)(2)M2+. Coexisting Na+, K+, Mg2+, and Ca2+ have little influence, but Cu2+ and Ni2+ have great influence on the adsorption of Fe3O4@PGMA-g-TETA-CSSNa toward Pb2+ and Cd2+. The adsorption selectivity of Fe3O4@PGMA-g-TETA-CSSNa toward heavy metal ions in their mixed solutions follows the following order: Cd2+ > Pb2+ > Cu2+ > Ni2+. The resulting adsorbent exhibited excellent magnetic separation, elution regeneration, and recycling performance. The present work provided a novel practical adsorbent for the rapid and highly efficient removal of heavy metal ions from actual wastewater.

Automated summary

In this study, a novel magnetic core-shell chelating adsorbent was fabricated and demonstrated to have high adsorption capacity for heavy metal ions. The adsorbent showed excellent separation, recovery, and recyclability properties.