Azurobine degradation using Fe2O3@multi-walled carbon nanotube activated peroxymonosulfate (PMS) under UVA-LED irradiation: performance, mechanism and environmental application

Food dyes are a large group of dyes which have been widely used in the food industry. The presence of them in aquatic media results in water pollution. In this work, a heterogeneous photo-assisted peroxymonosulfate (PMS) activation process was used to degrade Azorubine (AZB). Fe2O3 loaded on multi-wall carbon nanotube (Fe@MWCNT) was synthesized and applied to activate PMS under UVA-LED irradiation. Fe@MWCNT catalyst was characterized by XRD, FTIR, EDX-map, BET, FESEM, and TEM analyses. UVA-LED/Fe@MWCNT/PMS process removed around 95% of AZB from aqueous solution under pH= 5, PMS= 1.8 mM, and 130 mg/L Fe@MWCNT. Sulfate radicals showed a higher contribution for AZB degradation compared to hydroxyl radicals and singlet oxygen. Pseudo-first-order model was fitted on AZB degradation with a rate constant of 0.095 min(-1). Bicarbonate ions and humic acid had an ultra-inhibitory effect on the oxidative process. Carboxylic acids were monitored during AZB degradation, with the results indicating that aromatic rings of AZB were opened by the attack of sulfate and hydroxyl radicals. Six cycles of the catalyst reuse demonstrated no significant change in the performance of the UVA-LED/Fe@MWCNT/PMS process. The implementation of the UVA-LED/Fe@MWCNT/ PMS process was also successfully studied on other food dyes and real wastewater. UVA-LED/Fe@MWCNT/ PMS process was an efficient approach for the degradation of organic contaminants in water with high stability.

Automated summary

The study utilized Fe@MWCNT to activate PMS for the degradation of AZB, demonstrating high efficiency and stability in removing food dyes from aqueous solutions. Sulfate radicals played a major role in AZB degradation, followed by hydroxyl radicals and singlet oxygen. Environmental factors such as bicarbonate ions and humic acid were identified to have inhibitory effects, and the catalyst maintained stable performance during six cycles of reuse.