Silane-modified halloysite/Fe 3 O 4 nanocomposites: Simultaneous removal of Cr(VI) and Sb(V) and positive effects of Cr(VI) on Sb(V) adsorption

Abstract New adsorbents were successfully prepared by in-situ growing Fe3O4 nanoparticles on halloysite nanotubes (HNTs) followed by subsequent modification with silane coupling agents. The as-prepared composites were characterized by TEM, XRD, TGA, ATR-FTIR, BET, and Zeta potential. The results confirm that Fe3O4 nanoparticles were successfully decorated on internal nanotube surfaces and silane coupling agents were grafted onto the external surfaces. Among the four types of silane coupling agents modified HNTs/Fe3O4, anilino-methyl-triethoxysilane (KH-42) modified HNTs/Fe3O4 composite exhibits the highest capacity for single adsorption of Cr(VI) and simultaneously adsorption of Cr(VI) and Sb(V). Moreover, the maximum Sb(V) removal efficiency increases from 67.0% in the single-solute system to 98.9% in the bi-solute system, suggesting that the presence of Cr(VI) enhances the Sb(V) removal by m-HNTs/Fe3O4. ATR-FTIR and XPS results reveal the existence of N–O–Cr bonds on adsorbent surfaces in the corresponding single-solute system, while Cr–O–Sb binding forms in the bi-solute system, which is responsible for the synergistic promoting effect on simultaneous adsorption of Cr(VI) and Sb(V) by m-HNTs/Fe3O4. The present work evinces that m-HNTs/Fe3O4 holds the potential in treating industrial wastewater and natrual surface water with coexisting heavy metals such as Cr(VI) and Sb(V).