Mechanism of the improved Fe(III)/persulfate reaction by gallic acid for ibuprofen degradation

• Published in: Environmental pollution (1987) 2022-12, Vol.314, p.120318, Article 120318
• Main Authors: Li, Linyi, Zheng, Danqing, Gu, Xinyi, Sun, Chengju, Liu, Yankun, Dong, Wenbo, Wu, Yanlin
• Format: Article
• Language: English
• Subjects: Fe(III)/Fe(II) cycle; Ferric Compounds; Ferrous Compounds - chemistry; Gallic Acid; Ibuprofen; Oxidation-Reduction; Persulfate; Polyphenol; Polyphenols; Quinones; Reaction mechanism; Water Pollutants, Chemical - analysis
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2022.120318

Gallic acid (GA), a natural plant polyphenol, was applied as amendment of Fe(III)/persulfate (PS) system for ibuprofen (IBP) degradation in this study. The impacts of all agentia (GA, Fe(III), PS) concentration and initial pH values on IBP removal efficiency were investigated, and their corresponding observed pseudo-first-order rate constants (kobs) were calculated. The addition of GA has significantly improved elimination efficiency of IBP due to the enhanced Fe(III)/Fe(II) cycle. Electron paramagnetic resonance (EPR) results confirmed that SO4•−, HO• and O2•− were involved in GA/Fe(III)/PS system. However, quenching experiments further affirmed the impact of SO4•− and HO• towards IBP decomposition instead of O2•−, with contribution ratio to IBP removal was 69.12% and 30.88%, respectively. SO4•− was the main radicals formed by directly activation of PS with Fe(II), while HO• was the transformation product of SO4•−. Based on instrumental analysis (stopped-flow UV–vis spectrum and MS) and theoretical calculation, the potential reaction mechanism between GA and Fe(III) in the presence of PS was further proposed. GA complexed with Fe(III) firstly and the Fe(III)-GA complex was then converted into quinone substance, accompanied by the generation of Fe(II). Furthermore, the application of GA extended the optimal pH range to neutral as well, which made it a promising treatment in practical application. [Display omitted] •Gallic acid (GA) promoted IBP degradation and PS activation in Fe(Ⅲ)/PS system.•The Fe(Ⅲ)/Fe(Ⅱ) cycle was accelerated by GA.•SO4.•−, HO•, and O2•− were generated but O2•− did not react with IBP.•IBP was efficiently removed under neutral pH in GA/Fe(Ⅲ)/PS system.•The mechanism of the reactions between GA, Fe(III) and PS was proposed.