Converting inert MOF into ultrafine CoOx particles embedded on N-doped hierarchical carbon as robust catalyst for nitrophenol wastewater management under ambient conditions

Developing metal oxide catalysts with comparable activity to precious metals has become a hot but challenging area of research for wastewater purification. Herein, CoO x particles and nitrogen co-doped carbon with a hierarchical structure were designed and synthesized via a temperature-controlled pyrolysis strategy using inert Co-based metal–organic frameworks (Co-MOFs) as precursors. Unlike traditional methods, the exquisite pyrolysis of the Co-MOF at 400 °C enabling the CoO x particles with an average diameter of 6.8 nm to uniformly disperse, thus facilitating the formation of the optimized CoO x /CN-400 composite. Benefiting from the unique morphology and composition, CoO x /CN-400 exhibited improved redox property and exceptional activity for the reduction of nitrophenol to form the corresponding aminophenol compounds. The complete conversion of 4-nitrophenol over CoO x /CN-400 requires only 35 min with a rate constant of 0.12 min −1 , which is significantly higher than that of most non-noble metal catalysts and approaching some of the noble metal-based catalysts. Furthermore, leveraging the embedded CoO x particles, CoO x /CN-400 maintains its high catalytic efficiency even after six successive cycles, demonstrates an outstanding long-term catalytic capability and reusability. Finally, the mechanisms of 4-NP reduction have been hypothesized based on the combination of characterization and DTF calculations.