Cu0 incorporated cobalt/nitrogen doped carbonaceous frameworks derived from ZIF-67 (Cu@Co N C) as PMS activator for efficient degradation of naproxen: Direct electron transfer and 1O2 dominated nonradical mechanisms

In this study, zero valent copper (Cu0) was incorporated into ZIF-67 to construct Cu0 and cobalt/nitrogen doped carbonaceous frameworks x-Cu@CoNCy. The obtained Cu@CoNC was employed to activate PMS to degrade naproxen (NPX) in aqueous phase. Influencing factors on NPX degradation were investigated, including mole ratio of Cu/Co, pyrolysis temperature, pH, catalyst dosage, PMS concentration, and coexisting inorganic anions. In the presence of 0.5 mM PMS and 25 mg/L 1:3-Cu@CoNC900, complete degradation of NPX (50 μM) could be achieved in 20 min within a wide pH range of 3 to 10. The superior catalytic activity of Cu@CoNC900 for PMS activation was related to the increased surface –OH groups, accelerated electron transfer rate induced by Cu0 with strong conductivity, formed surface PMS complexes with high oxidation activity, and synergistic effect between Cu and Co. EPR analysis, radical scavenging and probe tests excluded the participation of SO4− and OH in NPX degradation. Nonradical pathways of electron transfer from NPX to PMS and 1O2 oxidation contributed to the excellent degradation. The 1:3-Cu@CoNC900 demonstrated a decent degradation performance even after five consecutive recycles with low cobalt and copper ions leaching due to the encapsulation of Co and Cu on N-doped porous carbon. Further, the intermediates of NPX degradation were identified, and three possible degradation pathways were proposed. Overall, this work provides a feasible strategy to improve the stability and catalytic activity of ZIF-67 by the incorporation of Cu0.