A dynamic two-step anoxic/oxic process using sulfidated nanoscale zerovalent iron (S-nZVI) was employed to degrade tetrabromobisphenol A (TBBPA). In the anoxic stage, TBBPA followed a four-step sequential debromination pathway and was completely transformed to bisphenol A (BPA) with the optimal S/Fe molar ratio of 0.3. S-nZVI inhibited H2 evolution and preserved the reducing capacity of Fe(0). Fe(0), rather than the formed FeS in S-nZVI, was responsible for TBBPA debromination. In the oxic stage, the product BPA was attacked by •OH, transformed to dihydroxybenzenes and benzoquinones, and eventually, achieved mineralization via ring-opening reactions. The sulfidation process facilitated •OH production through a two-electron transfer pathway by surface-bound Fe­(II), in which structural Fe­(II) in FeS and regenerated Fe­(II) from Fe­(III) reduction by Fe(0) played significant roles toward total BPA degradation. S-nZVI was transformed to S8 and α-FeOOH after the oxic treatment. After these two steps, complete degradation of TBBPA was achieved. This study demonstrated the feasibility that refractory contaminants could be completely degraded in the dynamic two-step anoxic/oxic process, thus broadening the utility of S-nZVI for environmental applications in water treatment.

Iron sulfide (FeS) nanoparticles have been applied for selenite (Se(IV)) remediation in recent decades. However, the easy aggregation and oxidization of FeS hamper their reactivity. In this study, in situ immobilization technology was applied to prepare FeS nanoparticle-impregnated alginate composite (FeS-SA) for Se(IV) remediation. FeS-SA removed 100% of the Se(IV) (0.13 mM), whereas pure nonstabilized FeS and sodium alginate (SA) beads eliminated only 27 and 20% of the Se(IV), respectively. The removal efficiency increased to 73% when pure stabilized FeS was used. Therefore, FeS-SA showed superior removal efficiency that was comparable with the joint effect of pure stabilized FeS and SA beads due to the homogeneous distribution of FeS in SA matrix. Furthermore, minor differences were established in the oxidation retardation effect of FeS exerted by SA beads under anoxic and oxic conditions. The biogenic regenerated FeS-SA still showed 40% removal efficiency for Se(IV) after five cycles due to the Fe leaching. XPS technique combined with the reference compounds and electron balance revealed that FeSe and metal selenium were the main selenium species after treatment. This in situ preparation of stabilized FeS-SA exhibited an excellent application prospect in the remediation of Se(IV).