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Reduction Pathways in Zero-Valent Iron Systems: Discussions Triggered by Research Approaches and Detection Methods
Shiying Yang, Wenjun Kuang
Prog Chem ›› 2025, Vol. 37 ›› Issue (7) : 1011-1024.
PDF(5887 KB)
PDF(5887 KB)
Reduction Pathways in Zero-Valent Iron Systems: Discussions Triggered by Research Approaches and Detection Methods
Zero-valent iron (ZVI) and its surface-modified materials have been widely used for the removal of various pollutants due to their excellent reduction properties. The three recognized potential reduction pathways of ZVI include direct electron transfer reduction, Fe(II) reduction, and atomic hydrogen reduction. Due to varying interpretations among researchers regarding the three reduction pathways and the diverse methods employed to detect them, recent studies have yielded differing conclusions on several critical aspects, including: (1) the dominant reduction pathway for pristine ZVI materials; (2) the impact of sulfur modification on the generation or recombination of atomic hydrogen; (3) the role of carbon modification in enhancing the reduction performance of ZVI through accelerated direct electron transfer or atomic hydrogen production; (4) and the underlying mechanisms by which different transition metal modifications influence the dominant reduction pathways of ZVI, among others. These discrepancies have sparked debates concerning the predominant reduction pathways involved in the removal of pollutants by ZVI and its surface-modified materials. This review systematically summarizes the following points: (1) the structure and modification principles of ZVI and its surface-modified materials; (2) the mechanisms and detection methods of the three reduction pathways in ZVI reduction systems; (3) the influence of different surface modification techniques (sulfur modification, carbon material modification, and transition metal modification) on the reduction pathways and the existing controversies; (4) the interference of environmental conditions (pH, coexisting ions, and natural organic matter) on the reduction pathways. Based on the reduction pathways, the review also presents prospects for future research directions, with the aim of addressing some of the current uncertainties in reduction pathway research and promoting a unified understanding of ZVI reduction pathways, thereby advancing scientific research and development in ZVI and its surface-modified materials.
1 Introduction
2 Iron as a starting point: ZVI and its surface modified materials
2.1 ZVI structure and pollutants removal
2.2 Structure and modification principles of sulfur-modified ZVI
2.3 Structure and modification principles of carbon-modified ZVI
2.4 Structure and modification principles of transition metal-modified ZVI
3 First glimpses: reduction pathways and its detection methods
3.1 Direct electron transfer reduction pathway
3.2 Fe(Ⅱ) reduction pathway
3.3 Atomic hydrogen reduction pathway
4 Manifestation of conflicts: the impact of surface modification on reduction pathways
4.1 Sulfurization modification
4.2 Carbon material modification
4.3 Transition metal modification
5 Echoes of the tributary: interference of environmental conditions
5.1 pH
5.2 Coexisting ions
5.3 Natural organic contaminants
6 Conclusion and outlook
zero-valent iron / surface modification technology / reduction / direct electron transfer / Fe(Ⅱ) / atomic hydrogen
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