Cobalt Nanoparticles Encapsulated in Nitrogen-Doped Carbons Derived from Co-Metal-Organic Frameworks with Superb Adsorption Capacity for Tetracycline

The enrichment of tetracycline (TC) in the environment will harm human and animal tissues and lead to bacterial resistance. The MIL or ZIF derived magnetic carbon adsorbents have great potential for the removal of TC, whereas its low concentration of metals limits the adsorption efficiency. By one-step annealing Co-hexamine coordination frameworks at 700 oC, the ultrahigh Co concentration (86.10 wt%) and abundant doped nitrogen (2.85 at%) are achieved in the nitrogen-doped carbons encapsulated cobalt nanoparticles (Co@NC-700). The optimized Co@NC-700 composite exhibits a supercolossal TC adsorption capacity of 3058 mg g-1, which is ~6 times that of the traditional adsorbents, and the removal capacity maintains at 94.22% after four cycles. The adsorption of TC follows Pseudo-second-order and Elovich kinetic models, suggesting a chemisorption process. The adsorption isotherm had good compatibility with Langmuir, Freundlich and Temkin models. Experiments and characterizations revealed the dominant effect of π-π electron donor-acceptor (EDA) interaction and surface complexation on the adsorption of TC. Density functional theory calculations demonstrate that the encapsulated cobalt formed complex bond with TC through the pore and pyridinic-N enhance the π-π EDA interaction. This work demonstrates a strategy of preparing magnetic carbon material with ultrahigh metal concentration, which opens up a new avenue for highly efficient adsorbent development in the removal of antibiotics and pollutants.