Carbon nanotubes in situ derived from bimetallic ZIF as efficient peroxymonosulfate activators for bisphenol A degradation via electron transfer

To develop high performance with wide pH adaptability catalysts for advanced oxidation processes, Co/N Co-doped carbon nanotubes encapsulating cobalt nanoparticles (Co@N-CNTs-x/y) were prepared by pyrolysis of dicyandiamide (DCD)-coated bimetallic zeolitic imidazole frameworks (Co_xZn_y-ZIF) rapidly synthesized in supercritical carbon dioxide (sc-CO₂). The in situ growth of carbon nanotubes resulted in a more uniform distribution of cobalt atoms, forming abundant Co-N_x structures, and effectively encapsulating cobalt nanoparticles within the nanotubes, thereby reducing cobalt leakage. The doping of zinc and its subsequent volatilization at high temperatures significantly impacted the Co-N_x doping ratio, the diameter of the nanotubes, and the size and dispersion of cobalt nanoparticles (Co NPs). A non-radical catalytic mechanism dominated by electron transfer was proposed for hollow-structured Co@N-CNTs-1/1, enabling it to exhibit high bisphenol A (BPA) degradation efficiency across a pH range of 3–11 and tolerate various inorganic anions.