Synthesis of ZIF-67 derived honeycomb porous Co/NC catalyst for AO7 degradation via activation of peroxymonosulfate

MOF-derived metal-carbon composite catalyst was an alternative high-efficient catalyst for activating peroxymonosulfate (PMS). In this study, a novel cobalt-carbon-nitrogen doped composite catalyst with honeycomb porous structure (Co-HPNC) was obtained through a simple strategy consisting of three steps: self-growth of ZIF-67 on the SiO2 core, pyrolysis, and NaOH etching away SiO2 core. The Co-HPNC exhibited an outstanding catalytic performance (98.1% in 10 min) to activate PMS for acid orange 7 (AO7) degradation. The observed reaction kinetic constant (0.4319 min−1) was 2.64 times superior to that of the unmodified Co/NC catalysis system (0.1636 min−1). In the meantime, the catalyst demonstrated a high PMS activation capacity over a wide pH range of 3–11 and strong adaptability to the high concentration of inorganic anions (Cl-, SO42-, and CO32–). After being recycled three times, the removal efficiency could still reach 92.7% in 25 min. The quenching tests and EPR spectrum illustrated the existence of radical and non-radical pathways, in which singlet oxygen was dominant during the degradation process. It was hypothesized that Co(0)/Co(Ⅱ)/Co(Ⅲ), pyridinic-N and pyrrolic-N contributed to the generation of hydroxyl and sulfate radicals, while C=O functional group and graphitic-N were catalytic sites for singlet oxygen. Finally, the radical electrophilic attacking sites of AO7 were calculated by the density functional theory (DFT), and the degradation routes of AO7 were speculated by GC–MS. The toxicity test illustrated that the Co-HPNC/PMS system was an environmental-friendly technology for AO7 degradation. The prepared Co-HPNC with a unique honeycomb porous structure presents a novel synthesis route for MOF-derived catalyst applied in the PMS activation system for wastewater treatment.