In situ growth of N-doped carbon nanotubes encapsulated nZVI as nanoconfinement catalyst for mitigating the hurdles of ferric cations leaching and low oxidant utilization in Fenton-like catalysis

The nanoscale zero-valent iron-based advanced oxidation processes (nZVI-AOPs) exemplify one of the most robust technologies for governing the emerging contaminants but are susceptible to the leaching issue of substantial dissolved iron species with intrinsically low Fenton reactivity, resulting in undesirable secondary pollution and the futile consumption of oxidants. Here, a chelation-assisted co-assembly nanoconfinement tactic was developed to achieve the self-assembly of nitrogen-doped carbon nanotubes embedded with Fe species, assisted by the melamine and bidentate N-ligand 1,10-Phenanthroline. Benefiting from the synergy of distinctive nanotube structure, uniform N doping, and well-encapsulated nZVI, the as-obtained Fe⁰@NCNTs-2 manifested decent efficiency for activating peroxymonosulfate (PMS) to eliminate and mineralize bisphenol A (BPA). The pod-like core-shell efficaciously protected the inner active sites and minimized the leakage of metal ions under various degradation processes. The nanoconfined structure endows Fe⁰@NCNTs-2 with a multi-site adsorption of PMS, along with enhancing the utilization efficiency of oxidants by over 50 %. Experimental results and density functional theory (DFT) calculations jointly divulged that the nanoconfined nZVI-mediated electronic metal-support interactions (EMSI) mechanism under the nanoconfinement was responsible for the lower adsorption energy and futile consumption of PMS on the Fe⁰@NCNTs surface and considerably hastened electron transfer, along with triggering the nonradical-dominated (¹O₂ and electron-transfer) oxidation mechanism and unraveling the reason for the wide-pH orientation and exceptional stability of nanoconfined catalysts in the complicated water matrix. The introduction of the nano-confinement strategy is conducive to promoting the vigorous development of nZVI-AOPs.