Reductive transformation of tetrabromobisphenol A by sulfidated nano zerovalent iron

Abstract

Recent studies showed that sulfidated nano zerovalent iron (S-nZVI) is a better alternative to non-sulfidated nano zerovalent iron (NS-nZVI) commonly used for contaminated site remediation. However, its reactivity with different halogenated pollutants such as tetrabromobisphenol A (TBBPA) remains unclear. In this study, we explored the reductive transformation of TBBPA by S-nZVI and compared it with that by NS-nZVI. The results showed that over 90% of the initial TBBPA (20 mg L−1) was transformed by S-nZVI within 24 h of reaction, which was 1.65 times as high as that for NS-nZVI. The TBBPA transformation by S-nZVI was well described by a pseudo-first-order kinetic model, whilst that by NS-nZVI was well fitted by a three-parameter single exponential decay model. After 11 weeks of aging, S-nZVI was still able to transform up to 56% of the initial TBBPA within 24 h of reaction; by contrast, the two-week aged NS-nZVI lost more than 95% of its original capacity to transform TBBPA. Moreover, S-nZVI showed only an approximately 20% decrease in its capacity to transform TBBPA in the seventh cycle, while NS-nZVI was no longer able to transform TBBPA in the fourth cycle. XPS analysis suggested the formation of FeS layer on S-nZVI surface and electrochemical analysis revealed an elevated electron transfer capacity of S-nZVI, which were likely responsible for the superior performances of S-nZVI in TBBPA transformation. While the transformation rate of TBBPA by S-nZVI decreased with increasing initial concentration of TBBPA, it showed an increasing trend with increasing S/Fe ratio and initial concentration of S-nZVI. The study indicated that S-nZVI has the potential to be a promising alternative to NS-nZVI for remediation of TBBPA-contaminated aquatic environments.