A citrate-loaded nano-zero-valent iron heterogeneous Fenton system for steroid estrogens degradation under different acidity levels: The effects and mechanisms

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2021-10, Vol.421, p.129967, Article 129967
• Main Authors: Yang, Shuo, Yu, Weiwei, Du, Banghao, Fan, Gongduan, Zhang, Zhi, Pu, Guibing, Yang, Wei, Wang, Qiang, Sun, Weizhe, Tang, Jingjing
• Format: Article
• Language: English
• Subjects: Citrate ligand; Coupling and degradation; Nano Zero Valent Iron; Reactive oxide species; Steroid estrogen
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2021.129967

[Display omitted] •An excellent performance nZVI heterogeneous catalyst was developed and optimized.•The enhancement mechanisms of citrate ligands to nZVI were comprehensively explored.•Citrates and their hydroxyl-rich fragments formed a special spatial network structure on nZVI surface.•A degradation mechanism different from the traditional Fenton-like reaction was proposed. Today, the steroid estrogens (SEs) discharged with non-point source pollutions have brought potential risks to the environment. It is necessary to develop new restoration strategies for SEs. In this study, a heterogeneous nano-zero-valent iron Fenton system loaded with citrate ligands (C-nZVI) was proposed. It obviously enhanced the degradation rates of 17β-estradiol (17β-E2), and the degradation efficiency under neutral condition was also enhanced by 4.59 times. The characterization of C-nZVI showed that citrates and their hydroxyl-rich fragments formed a spatial network structure and covered on its surface. This allowed C-nZVI to overcome most of the inherent defects of nZVI and had ideal abilities to resist agglomeration, acid corrosion, and oxidation. Same as the traditional Fenton-like reaction, the generation of hydroxyl radicals (·OH) and superoxide radicals (·O2–) was the main way for C-nZVI to degrade 17β-E2. The ligands as the ions transport channel further stimulated the excitation of ·OH and ·O2–, and the singlet oxygen (1O2) was also found to play a role in the latter part of the reaction. However, C-nZVI had a special mechanism of first coupling between citrate ligands and 17β-E2, as well as subsequent degradation by ROSs, which might be the reason why C-nZVI has a much faster degradation efficiency than the general nZVI. And the degradation process of 17β-E2 showed its four rings might be destroyed one by one starting from the benzene ring. Therefore, this heterogeneous Fenton system assisted by chelating agent ligands has a certain value for the research of water emergency restoration.