Highly dispersed and stable nano zero-valent iron doped electrospun carbon nanofiber composite for aqueous hexavalent chromium removal

Abstract

In this work, a nZVI doped electrospun carbon nanofiber (nZVI-CNF) composite was prepared and applied for aqueous hexavalent chromium (Cr(vi)) removal. Firstly, FeCl₃/PAN nanofibers were prepared by a simple electrospinning method; Then, nZVI-CNFs were obtained by carbonization of FeCl₃/PAN nanofibers at 800 °C. The surface morphology and internal structure of nZVI-CNFs were characterized by SEM and TEM, showing that the uniformly dispersed nZVI particles were well integrated into the carbon layer structure. The Cr(vi) removal efficiency of nZVI-CNFs was 91.5% with a Cr(vi) concentration of 10 mg L^-1 and the mechanism was further studied by XRD and XPS. Meanwhile, the nZVI-CNFs exhibited good stability over a wide range of pH values from 4-8 and a long time placement stability. Furthermore, nZVI-CNFs can be used as a filter membrane for continuous treatment of wastewater, suggesting great potential for practical application.

Scheme 1. The schematic illustration of the preparation process of nZVI-CNFs composite.

Fig. 1. The different magnification SEM images (A, C and D); the diameter distribution (B); and the XRD pattern (E) of nZVI-CNFs before Cr(vi) removal.

Fig. 2. The TEM images (A and B); HR-TEM images (C and D); Element mapping of C, O, N and Fe (F) from (E) of nZVI-CNFs before Cr(vi) removal.

Fig. 3. The comparison of Cr(vi) removal efficiency by nZVI-CNFs with different nZVI contents and pure nZVI.

Fig. 4. The Freundlich (A) and Langmuir (B) isothermal models for Cr(vi) removal process.

Fig. 5. The Cr(vi) removal efficiency at different pH values ranging from 4 to 8 (A); the stability of the nZVI-CNFs composite at open environment (B); XRD patterns of nZVI-CNFs at 7 and 14 days (C).

Fig. 6. The schematic diagram of simulated reactor again to get repeated treatment (A); the Cr(vi) removal per each cycle of treatment (B).

Fig. 7. XRD patterns (A); XPS survey (B) and Fe_2p XPS spectra (C) of nZVI-CNFs before and after Cr(vi) removal; Cr_2p XPS spectra of nZVI-CNFs after Cr(vi) removal (D).

Fig. 8. Analysis of nZVI-CNFs after Cr(vi) removal: SEM images with different magnifications (A, B, C and E); TEM images (D); EDX element mapping of Fe, Cr, C and O elements obtained (F) from (E); and the possible mechanisms for Cr(vi) adsorption and reduction by nZVI-CNFs (G).