Size-controlled biosynthesis of FeS nanoparticles for efficient removal of aqueous Cr(VI)

In this study, biogenic iron sulfide nanoparticles (FeS NPs) were synthesized by Shewanella and used for Cr(VI) removal. To control the size of FeS NPs, the biological S(-II) releasing rate was proposed as the key parameter in Fe(III) reduction and was subtly tuned with the aid of a kinetic model. Field emission scanning electron microscope (FESEM) observation revealed that gradually increased S(-II) releasing rate lead to the formation of FeS NPs with size from 30 nm to 90 nm. Impressively, the biogenic FeS NPs with 30-40 nm showed high removal rate and large removal capacity (565.6 mg/g) for removal of aqueous Cr(VI). Further analyses revealed that the improved performance of small FeS NPs was ascribed to the reduced passivation of FeS. Therefore, this study provided a facile approach for size-controlled biosynthesis of FeS NPs, and demonstrated the promise to use biogenic FeS NPs for chromate remediation.