Insitu growth of ZIF-8 on CoAl layered double hydroxide/carbon fiber composites for highly efficient absorptive removal of hexavalent chromium from aqueous solutions

Waste water pollution containing heavy metal ions has raised wide concern in environmental sustainability, calling for the development of high-efficiency and low-cost materials for waste water treating. Herein, a series of carbon fiber/Co-Al layered double hydroxide/zeolitic imidazolate framework-8 (CF/LDH/ZIF-8) composites were synthesized and used for the high-efficiency elimination of toxic chromium Cr (VI) from aqueous solutions. The morphology, phase composition, phase structure of the CF/LDH/ZIF-8 composites were investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and nitrogen adsorption-desorption methods, respectively. The LDH/ZIF-8 films on the CF showed a homogeneous micro/nano scale porous structure , which was composed of Co Al LDH nanoplates and ZIF-8 nanocrystals. The nanocomposites showed high specific surface area of 156.9 m 2  g −1 and pore diameters distributed almost in a narrow range of 2.5–8.3 nm when the molar ratio of Al 3+ /Co 2+ reached to 2:3. High-efficiency elimination of toxic chromium Cr (VI) by the CF/LDH/ZIF-8 composites was confirmed by the absorption test which showed the high absorption capacities of Cr (VI) (378 mg/g). With the presence of CF/LDH/ZIF-8 composites in solution, toxic chromium Cr (VI) can be removed quickly, and the removal efficiency approached 99.3% approximately. Further, the results of cyclic tests indicated that the hierarchical CF/LDH/ZIF-8 composites exhibit excellent cyclic stability and can be fast regenerated in NaOH at 25 °C, rendering a widely application in environmentally friendly and high efficiency material for waste water treatment .