Nitrogen-doped carbon nanotubes encapsulating Fe/Zn nanoparticles as a persulfate activator for sulfamethoxazole degradation: role of encapsulated bimetallic nanoparticles and nonradical reaction

In this work, the carbon nanotubes (CNTs) encapsulating Zn and Fe bimetallic nanoparticles (FeZn@NC) were synthesized through a one-pot pyrolytic strategy. The persulfate (PS) activation ability of FeZn@NC with various ratios of Fe and Zn was determined by sulfamethoxazole (SMX) degradation. The results indicated that the iron played a key role in forming external CNTs and the catalytic activity of FeZn@NC was mainly based on the encapsulated FeZn nanoparticles. In addition, PS activation was greatly strengthened by the heterostructure of FeZn@NC. Free radical quenching experiments and electron paramagnetic resonance (EPR) spectra suggested that the singlet oxygen was the key reactive oxygen species for SMX degradation. The activity of pyridinic-N, pyrrolic-N and graphitic-N on external CNTs was analyzed by theoretical calculations, which showed the pyridinic-N possessed strong adsorptive ability to activate PS to degenerate sulfate radicals.