Catalytic degradation of acetaminophen by Fe and N Co-doped multi-walled carbon nanotubes

An Fe and N co-doped carbon nanotube (CNT) (Fe/N-CNT) was successfully prepared using a simple hydrothermal method. CNT, Fe doped CNTs (Fe-CNT), N doped CNTs (N-CNT), and Fe/N-CNT were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and zeta potential analysis. The catalytic activities of the materials were investigated via pharmaceutical (acetaminophen, ACT) degradation using persulfate (PS). The ACT removal rate was in the order: Fe-CNT > N-CNT > Fe-CNT > CNT, for 30 min with 10 mg/L ACT, 0.05 g/L materials, and 0.08 mM PS. The doped N existed as pyridinic-N, pyrrolic-N/N-Fe, graphitic-N, and oxidized-N, while the doped Fe existed as Fe-N, FeO/Fe₃O₄, and Fe₂O₃/FeOOH at the edge. The rates of ACT removal and PS decomposition were well correlated with pyrrolic-N/N-Fe. The ACT removal in the Fe/N-CNT + PS system was as high as >98.4% and was not significantly affected by the initial pH of 2.0-8.2 and ten consecutive uses. However, natural organic matter (NOM) inhibited ACT removal by the accumulation on Fe/N-CNT. The results of ACT removal in the presence of radical scavengers, PS decomposition, and cyclic voltammetry showed that the ACT removal was dominantly attributed to a non-radical pathway with the accelerated electron transfer from ACT to PS through the Fe/N-CNT. The results in this study strongly suggest that the Fe/N-CNT + PS system is an excellent process for the degradation of refractory organic pollutants in various water matrices with improved performance and stability attributed by non-radical pathway.