Enhanced tetrabromobisphenol A debromination by nanoscale zero valent iron particles sulfidated with S0 dissolved in ethanol

Abstract

Modification of nanoscale zero-valent iron (nZVI) with reducing sulfur compounds has proven to improve the reactivity of nZVI towards recalcitrant halogenated organic contaminants. In this study, we develop a novel method for the preparation of sulfidated nZVI (S-nZVI) with S⁰ (a low cost and available reducing sulfur agent) dissolved in ethanol under mild conditions and apply it for the transformation of tetrabromobisphenol A (TBBPA), a potential persistent organic pollutant. Surface analysis shows that S⁰ dissolved in ethanol has been successfully doped into nZVI via a reaction with Fe⁰ to form a relatively homogeneous layer of FeS/FeS₂ on the nZVI surface. The H₂ production test and the electrochemical analysis show that the FeS/FeS₂ layer not only slows the H₂ evolution reaction but also enhances the electron transfer. Debromination kinetics indicate that the resulting S-nZVI with a S/Fe ratio of 0.015–0.05 possesses higher debromination activity for TBBPA and its debromination products (i.e., tri-BBPA, di-BBPA, mono-BBPA and BPA) in comparison with nZVI. Among them, S-nZVI at a S/Fe of 0.025 (S-nZVI^S-0.025) has the greatest debromination rate constant (k_obs) of 1.19 ± 0.071 h⁻¹ for TBBPA. It debrominates TBBPA at a faster rate than other conventional S-nZVI made from Na₂S and Na₂S₂O₄ and has been successfully applied in the treatment of TBBPA-spiked environmental water samples (including river water, groundwater, and tap water). The results suggest that the modification of nZVI with S⁰ dissolved in ethanol is a simple, safe, inexpensive, and effective sulfidation technique, which can be applied for the large-scale production of S-nZVI for treating contaminated water.