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 m(2)/g) than Bi-Fe/BC (103.26 m(2)/g), increasing the number of active sites accessible for PMS activation. Reactive species analysis revealed the presence of SO4 center dot-, center dot OH, O-1(2)center dot-, and O-1(2) species, with SO4 center dot- and O-1(2) 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 center dot- 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.