Promoted generation strategies and corresponding roles of singlet oxygen in activation of persulfate by nanoscale zero-valent iron systems

In recent years, the remediation of water contamination through non-radical pathways by singlet oxygen (1O2) has caught scientists’ increasing attention owing to the adaptability to wider pH range and superior selectivity to target pollutants. In this review, strategies of promoting the generation of 1O2 in persulfate activation over nanoscale zero-valent iron (nZVI) and the corresponding roles of 1O2 in degrading pollutants are summarized systematically, chiefly illustrating the mechanisms of persulfate activation to produce 1O2. The reasons underlying improvements in the degradation of organic pollutants originate from increased generation and enhanced activity of 1O2 in modified systems and coupling systems based on nZVI. Additionally, in order to figure out how external environment affects the generation and behavior of 1O2, several major influence factors are also compared and evaluated. On the whole, this paper draws a relatively clear picture of 1O2 in the combination of persulfate and nZVI-based systems, opening novel perspective of capitalizing on the merits of 1O2 to deal with the increasingly troublesome problem of water pollution.