Combining high electron transfer efficiency and oxidation resistance in nZVI with coatings of microbial extracellular polymeric substances to enhance Sb(V) reduction and adsorption

Abstract

In this work, we prepared microbial extracellular polymeric substances-coated nano zero valent iron (EPS@nZVI) for Sb(V) removal. Batch adsorption experiments showed that the synthesized EPS@nZVI had superior maximum adsorption capacity (202 mg/g at pH = 5) for Sb(V), much higher than that of bare nZVI especially under nonacidic conditions. The adsorption results fit the pseudo-second-order kinetic model and the Redlich-Peterson model well, implying that the adsorption was more like a chemical adsorption process. The spectral analysis showed that EPS could protect inner Fe0 from air, preventing nZVI from generating a passivation layer on the surface, and decreasing the concentration of hydroxyl radicals in aqueous environment, which increased the reactivity of nZVI and strengthened the reducibility and adsorbability of nZVI. The coated EPS can improve the reactivity of nZVI instead of inhibiting its electron transfer. Moreover, the electrostatic repulsion between EPS@nZVI and Sb(OH)6− was decreased compared to that of bare nZVI after the introduction of EPS. The functional groups of EPS could play a significant role in the reduction adsorption, especially under alkaline conditions where nZVI was passivated. This work proved that EPS@nZVI has great prospects in simultaneously combining the reduction activity of nZVI in water and its stability in air.