Magnetic Fe3O4/attapulgite hybrids for Cd(II) adsorption: Performance, mechanism and recovery

Herein, a Fe3O4 decorated attapulgite adsorbent (FA) is fabricated for the removal of Cd(II) from wastewater, and subsequently a feasible strategy for converting the saturated waste adsorbent to CdS/FA photocatalyst is reported. Owing to the in situ growth of Fe3O4 on the attapulgite (ATP), the FA adsorbents exhibit enlarged surface area and increased adsorption sites. More importantly, the strong interaction between Fe3O4 and ATP leads to changes of coordination environment around the O‒Fe‒O bond with the ATP. Based on the results of density functional theory calculations, the electrons are more readily transferred from Fe to O, and the hanging O atoms with more electronegativity act as the efficient adsorption sites for Cd(II), efficiently improving the adsorption performance of the Fe3O4 phases. Furthermore, the waste FA adsorbent could be conveniently separated from the treated water by magnets and converted to CdS/FA photocatalyst, which exhibits satisfying degradation efficiency for tetracycline with low concentration. This work provides a potential strategy to optimize the ATP-based materials for heavy ions adsorption and reutilize the waste adsorbents.