Antimony removal by a magnetic TiO2/SiO2/Fe3O4 nanosphere and influence of model dissolved organic matter

Abstract Antimony (Sb) pollution is attracting increasing international concerns. In this work, a novel magnetic nanosphere TiO2/SiO2/Fe3O4 (TSF) was synthesized for antimony removal. The influence of four amino acids on antimony removal by TSF and the associated mechanisms were systematically investigated. The results showed that TSF has high Sb removal efficiency reaching up to 96%. The presence of lysine, glutamate, and arginine did not alter antimony removal at pH = 2–11, because they were not sorbed to TSF and did not bind antimony in the aqueous phase. In contrast, cysteine-led reduction in antimony removal by TSF tended to be more pronounced when pH increased from 2 to 11, with reduction percentage increasing from 0 at pH 2 to 79% at pH 11. XPS and RAMAN analysis showed the weak interaction between antimony and –NH2 and –COOH, but strong interaction with -SH. When solution pH increased from 2 to 11, the speciation changes of antimony, TSF, and cysteine thus their interaction changes caused antimony removal reduction. At pH = 2, cysteine formed intermolecular hydrogen bond network, limiting the coordination between -SH and antimony. When pH increased to 6 and finally to 11, the hydrogen bond network was gradually broken, and the -SH group gradually lost H+ and became -S− which more readily complexed with antimony. Therefore, competition of cysteine in liquid phase with TSF for antimony was enhanced. The complexation of antimony and cysteine in solution increased with increasing cysteine concentration, hence antimony removal efficiency by TSF gradually decreased.