Enhanced removal of Sb(III) and Sb(V) using biosynthesized iron sulfide nanoparticles: Identification of biomolecules in the capping layer and its functions

As a green and sustainable technology, biosynthesis of iron sulfide nanoparticles (FeS) has attracted increasing recent attention. However, a comprehensive analysis of the biomolecular structure and function of the capping layer is currently lacking and is now considered essential because the reactivity of biosynthesized FeS is believed to be highly dependent on this capping layer. Here, FeS (PML-FeS) synthesized by Pinus massoniana Lamb extracts were used to remove Sb(III) and Sb(V) and in so doing gain a better understanding of the function of the capping layer via comparison with the removal of both Sb species by bare-FeS. The maximum removal efficiencies of Sb (III) and Sb(V) (100 and 87.6%) obtained by PML-FeS, were much higher than that obtained by bare-FeS (78.7 and 61.2%), indicating that the biomolecules in the capping layer enhanced the removal capacity. Advanced characterizations confirmed that the removal of Sb(III) and Sb(V) by the capping layer was based predominantly on adsorption, while the removal of Sb(III) and Sb(V) by bare-FeS exhibited both adsorption and oxidation behavior. This suggested a synergistic effect in PML-FeS between the capping layer and bare-FeS. Liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) confirmed that biomolecules in the capping layer were enriched in -OH and -COOH, demonstrating that oxygen-containing functional groups play a significant role in provision of active binding sites for Sb removal.