Porous N-doped carbon nanospheres with encapsulated cobalt nanocrystals for persulfate activation to degrade tetracycline

Metal-based nitrogen-doped carbon (M-N-C) materials have attracted wide attention owing to their effectiveness in activating persulfate (PS) for remediation of organic pollutants. Herein, we report a simple method of pyrolysis and simultaneous self-reduction for preparing porous N-doped carbon nanospheres encapsulated with cobalt nanocrystals (Co/p-CN) as a composite catalyst for PS activation. Co/p-CN composite was characterized by powder X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The composite exhibits a high surface area and rich mesoporous structure, which is conducive to exposing more active sites and facilitating mass transport of the matrix. N-doped carbon nanospheres were used to protect the cobalt nanocrystals and N doping helped to fix the Co metal through coordination for manipulating its catalytic activity. After systematic study on the preparation conditions of Co/p-CN composite, it was found that the best Co/p–CN–900 (pyrolyzed at 900 °C) could efficiently degrade tetracycline (TC) in 40 min. The quenching experiments showed that Co species in porous N-doped carbon nanospheres caused the oxidation through radicals and nonradicals (SO₄^•−, •OH, O₂^•− and ¹O₂) in the presence of PS. PS activation of Co/p–CN–900 composite involved the mediated electron-transfer for disintegration of refractory organic TC.