Great increasing N content in Fe-embedded carbon nanotubes to effectively activate persulfate for radical and nonradical degradation of organic contaminants

N atoms in carbonaceous catalysts are usually considered as the key active centers for catalytic/activated reactions. However, the raise of N content in metal-carbonaceous composites is still a great challenge. In this work, the N content in Fe-embedded carbon nanotubes (Fe@CNTs) was greatly enriched via a Zn-N linkage process, giving Fe-embedded N-rich carbon nanotubes (Fe@NRCNTs). The N content of Fe@NRCNTs was up to 7.43 atom%, reaching the highest value among other Fe-embedded carbonaceous materials. Zn-N linkage could induce more active C sites in g-C3N4 intermediate for N-doping and inhibit the release of N-containing gases, resulting in N enrichment during the formation of Fe@NRCNTs. More importantly, the as-obtained Fe@NRCNTs exhibited excellent performance towards persulfate activation for tetracycline degradation, and its rate constant was four times higher than that of Fe@CNTs. The high N content provided more active site for nonradical activation, and also accelerated the electron transfer between Fe and CNTs, beneficial for radical activation. Furthermore, Fe@NRCNTs could work in a very wide pH range (2.2–10.3), accompanying with high adaptability and reusability. This work provided a feasible strategy to increase N content in metal-embedded carbonaceous materials for highly efficient radical and nonradical persulfate activation.