Synergistic mechanisms of Ni/Fe@Fe3O4-g-C3N4 (NFFOCN) nanocomposites in efficient Cr(VI) removal from aqueous solution

Nowadays, Ni/Fe bimetallic nanocomposites have shown great potential for removing Cr(VI). However, the action of Ni0 in Cr(VI) removal is still controversial, which was studied in this work. In this study, Ni/Fe@Fe3O4g-C3N4 (NFFOCN) nanocomposites were applied to remove Cr(VI) from aqueous solutions and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and other methods. Batch experiments were conducted to evaluate the Cr(VI) removal performance. Experimental results demonstrated that under optimal operating conditions (pH 5.5, 10 mg/L Cr(VI), 0.3 g/L NFFOCN, 30 degrees C), a Cr(VI) removal efficiency of 90.78% was achieved within 50 min. Theoretical maximum adsorption capacity was calculated to be 36.101 mg/g. Combining experimental and characterization results, it could be concluded that Cr(VI) removal was attributed to the synergistic effect of the NFFOCN components. Ni0 not only participated directly in the reduction of Cr(VI) as an electron donor, but also converted the corrosion product H2 of nano-zerovalent iron (nZVI) into highly reducible atomic hydrogen (& sdot;H) to remove Cr(VI). Additionally, Ni0 could form a primary battery with nZVI, facilitating the electron transfer between nZVI and Cr(VI). NZVI and its derivatives, Fe2+ ions and green rust, were responsible for Cr(VI) reduction. Furthermore, the presence of Fe3O4 and carbon nitride (g-C3N4) improved the stability and reactivity of the nanocomposites.