Model simulation and mechanism of Fe(0/II/III) cycle activated persulfate degradation of methylparaben based on hydroxylamine enhanced nano-zero-valent iron

The mechanism of Fe2+-activated peroxodisulfate (PDS) by hydroxylamine (HA) has been investigated, however, nano zero-valent iron-activated persulfate (nZVI/PDS) has a more optimal effect and needs further investigation. This study investigated the addition of HA to nZVI/PDS to improve Fe2+ regeneration and accelerate methyl-paraben (MP) degradation by Fe (0/II/III) cycle. After 60 min of reaction, the HA-enhanced nZVI/PDS (HA/ nZVI/PDS) system afforded a 21% increase in MP degradation, reaching 93.26% (1 mM HA, 1 mM nZVI, and 2 mM PDS). nZVI/PDS system was a second-order reaction, but after adding HA, the reaction was more suitable for the first-order reaction. The addition of HA effectively promoted the reduction of Fe3+ to Fe2+ to improve the effect and reaction rate of PDS degradation of MP (k increased from 0.0127 min-1 to 0.0198 min-1) and broadened the reaction pH range. The results of various characterizations of nZVI before and after the reaction revealed that nZVI changed from a spherical structure to a bundle structure and was slightly oxidized. Changes in the Fe2+ and Fe3+ concentrations as well as in the pH of the reaction systems were monitored and the possible reactions of the HA/nZVI/PDS system were derived for the first time (knZVI/PDS < 3.7 x 106 M-1 s- 1, kFe3+/NH2O. > 4.2 min-1). 12 potential compounds were investigated and MP breakdown pathways were speculated; hy-droxylation was determined to be the most important pathway of degradation. And the HA/nZVI/PDS system had universal applicability.

Automated summary

This study investigated the addition of hydroxylamine (HA) to nano zero-valent iron-activated persulfate (nZVI/PDS) to improve the degradation of methyl-paraben (MP). The results showed that the HA/nZVI/PDS system could enhance the degradation of MP and broaden the reaction pH range. Additionally, the study speculated on the degradation pathways of MP and the universal applicability of the HA/nZVI/PDS system.