Preparation of the Carbonized Zif-8@PAN Nanofiber Membrane for Cadmium Ion Adsorption.

The zeolitic imidazolate framework (ZIF-8)@polyacrylonitrile (PAN) nanofiber membrane was prepared and carbonized for heavy metal cadmium ion (Cd) adsorption in aqueous medium. Zinc oxide (ZnO) was first sputtered onto the surface of the PAN electrospun nanofiber membrane to provide a metal ion source. Then, the ZIF-8@PAN nanofiber membrane was prepared via in situ solvothermal reaction and carbonized in a tube furnace at 900 °C under a N atmosphere to enhance adsorption performance. The synthesized ZIF-8 particles with polyhedral structure were uniformly immobilized on the surface of the PAN electrospun nanofiber membrane. After being heated at 900 °C, the polygonal ZIF-8 shrank, and the carbonized ZIF-8@PAN nanofiber membrane was obtained. Compared with the nanofiber membrane without being carbonized, the adsorption capacity of the carbonized ZIF-8@PAN nanofiber membrane reached 102 mg L, and its Cd adsorption efficiency could be more than 90% under the adsorption temperature of 35 °C and solution of pH = 7.5 conditions. According to the adsorption thermodynamics analysis, the Cd adsorption process of the carbonized ZIF-8@PAN nanofiber membrane was spontaneous. The whole Cd adsorption process was more suitably described by the pseudo second-order adsorption kinetics model, indicating that there exists a chemical adsorption mechanism besides physical adsorption.