Synergistic enhancement of peroxymonosulfate activation by bimetallic (Bi, Fe) supported NaHCO3 activated and urea-modified biochar for sulfamethoxazole degradation: DFT calculations, toxicity assessments, and mechanistic studies

Advanced oxidation processes based on Fenton-like reactions to activate peroxymonosulfate (PMS) for degrading antibiotics face challenges due to insufficient PMS activation and Fe (III)/Fe (II) recycling. Therefore, developing iron-based bimetallic catalyst for sufficient PMS activation and Fe (III)/Fe (II) recycling is critical. Herein, bimetallic (Bi, Fe) NPs supported NaHCO3 activated and urea-modified biochar (Bi-Fe/N-BC) composite were synthesized through two-step hydrothermal method. The Bi-Fe/N-BC/PMS system reached 96.6% conversion, which is approximately 6.01 times greater than BC (k = 0.0110 min−1), 2.44 times greater than N-BC (k = 0.0273 min−1), and 1.84 times greater than Bi-Fe/BC (k = 0.0362 min−1) and 1.78 times greater than Bi-Fe/N-BC system (k = 0.0374). The enhanced performance could be attributed to Fe (III)/Fe (II) recycling facilitated by Bi (I)/Bi (III) and Bi (II)/Bi (III) couples and the formation of nitrogen-active sites, which resulted in synergistic enhancement between the non-radical and radical mechanisms. Furthermore, the composite Bi-Fe/N-BC exhibited a higher surface area (147.50 m2/g) than Bi-Fe/BC (103.26 m2/g), increasing the number of active sites accessible for PMS activation. Reactive species analysis revealed the presence of SO4•─, •OH, O2•−, and 1O2 species, with SO4•─ and 1O2 were major contributors. The impact of coexisting inorganic anions revealed that the HCO3− ion exhibited the most pronounced inhibitory effect due to the production of less reactive CO3•─ radical. This study combined experimental and computational methods to enrich our understanding of the activation mechanisms, transformation pathways, toxicity of intermediates, and factors governing the N-BC-supported Bi-Fe/PMS system.