Efficient removal of Sb(V) in textile wastewater through novel amorphous Si-doped Fe oxide composites: Phase composition, stability and adsorption mechanism

The development of amorphous iron oxide-based composites for the Sb(V) removal is limited by their easy phase transformation, aggregation, and unstable nature. Herein, novel modified Si-doped Fe oxide composites (SFOC) were prepared to break through the current obstacle. Characterization results of SFOC with a suitable amount of doped Si indicated that the coordination interaction between Si-OH and Fe-OH blocked the crystal growth sites in both Si and Fe oxide, and the crystal unit cells of same element were difficult to contact with each other. Hence, the crystal growth of Si and Fe oxide was retarded and their unit particle size became smaller. Meanwhile, the crystal phase transformation of amorphous ferrihydrite was prevented and the aggregation extent of Fe oxide was greatly decreased after Si doping. These changes caused that more Fe vacancies were generated on the surface of amorphous Fe oxide unit and the surface area of SFOCs also increased, resulting in the great increasement of exposed Fe hydroxyl groups in SFOC. As compared to pristine Fe oxide, the optimal SFOC₁₀ with Fe/Si molar ratio of 10:1 exhibited the highest surface area of 363.9 m²/g, the maximum Sb(V) removal capacity of 176.1 mg/g, and higher selective Sb(V) adsorption performance. The introduction of Si oxide also endowed SFOC₁₀ with much better phase stability and Sb(V) removal capacity during the long cyclic adsorption-desorption process. Moreover, the inner-sphere complexation of Fe-OH and Sb(OH)₆⁻ played a key role in adsorption. Furthermore, optimal SFOC₁₀ was sufficient for the Sb(V) removal from real textile wastewater in both the batch and dynamic column adsorption processes. © 2020 Elsevier B.V.