Fe Immobilized within Accordion-Like Tubular Carbon Nitride As a Catalyst for the Fenton-Like Degradation of Ranitidine: Synergetic Roles of ^•OH and ¹O₂

Advanced oxidation processes (AOPs) based on H₂O₂ are considered effective strategies to remove emerging organic pollutants from water bodies. In this work, Fenton-like Fe-based catalysts were fabricated through a simple hydrothermal calcination method. Fe was immobilized within carbon nitride with a structure of accordion-like hollow nanotubes enriched with open chinks (atCN). The Fe-atCN catalysts were employed for Fenton-like reactions to degrade ranitidine (RAN). Due to the unique structure of the atCN substrate and the Fe-N interactions established between highly dispersed Fe sites and the atCN matrix, the 3.4Fe-atCN/H₂O₂ system was able to completely eliminate RAN within 30 min at an initial pH of 3 (k = 0.143 min^-1). It also remained highly active after four cycles of regeneration. Moreover, the 3.4Fe-atCN/H₂O₂ system showed good adaptability in a pH range of 3-6, with coexisting inorganic anions, and in diverse water bodies. Good oxidative activities on various pollutants were also demonstrated, including sulfamethoxazole, tetracycline, 4-chlorophenol, and methyl orange. Afterward, mechanism exploration suggested that the dominant reactive oxygen species driving the degradation of RAN in the 3.4Fe-atCN/H₂O₂ system were not only the generally reported ^•OH but also the unexpected nonradical of ¹O₂. The activation mechanism of 3.4Fe-atCN to H₂O₂, intermediates, and degradation pathways of RAN were then unveiled for providing further guidance to the development of Fenton-like technology.