Peroxymonosulfate activation by Mg-introduced Fe-N carbon nanotubes to accelerate sulfamethoxazole degradation: Singlet oxygen-dominated nonradical pathway

[Display omitted] •Mg-introduced Fe-N doped carbon nanotubes found a shift in PMS activation from radical to nonradical.•1O2 plays a dominant role in the degradation process of SMX.•The activation mechanism is less susceptible to the effects of solution pH, ionic strength, and anion.•Possible degradation pathways of SMX were analyzed by DFT calculations and HPLC-MS.•T.E.S.T toxicity assessment method was used to analyze the intermediates with lower ecotoxicity than SMX. Here, Mg-introduced Fe-N carbon nanotube catalysts (FeMg@NCNTs) were prepared for peroxymonosulfate (PMS). Experiments suggested that the introduction of Mg improved the removal of sulfamethoxazole (SMX) and found a transformation from the original radical pathway to a nonradical pathway dominated by singlet oxygen (1O2). XPS characterization demonstrated an enhanced pyridinic N content with the introduction of Mg. SMX degradation was not inhibited by pH, coexisting ions, or humic acid (HA). The free radical scavengers and electron paramagnetic resonance (EPR) indicate that the primary reactive substance was 1O2. Experimentally, 1O2 was proven to have a predominant effect on the degradation of SMX. The concentration of 1O2 increased 6.37 times after the introduction of Mg. Four decomposition pathways and three fragile sites for SMX were proposed by DFT calculations and HPLC-MS. The toxicity estimation software tool (T.E.S.T) analyzed the intermediates with lower ecotoxicity than SMX. The different contaminants (CIP, BPA, TBBPA, TCS, TC and Rh B) had a removal rate of more than 99% at 60 min except TC. The removal rates of SMX in tap water, river water and lake water were 100%, 96.6% and 93.1% in 40 min, respectively. The SMX degradation efficiency remained good after 5 cycles of the experiment. FeMg@NCNTs hydrogel catalyst continuous flow device exceeded 90% within 15 h for SMX removal efficiency and the Rh B is always running at 99% removal rate. In conclusion, this work provides a singlet oxygen-dominated non-radical pathway activating material and provides a new option for antibiotic wastewater degradation and practical applications.