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 Ni 0 in Cr(VI) removal is still controversial, which was studied in this work. In this study, Ni/Fe@Fe 3 O 4 -g-C 3 N 4 (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°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. Ni 0 not only participated directly in the reduction of Cr(VI) as an electron donor, but also converted the corrosion product H 2 of nano-zero-valent iron (nZVI) into highly reducible atomic hydrogen (·H) to remove Cr(VI). Additionally, Ni 0 could form a primary battery with nZVI, facilitating the electron transfer between nZVI and Cr(VI). NZVI and its derivatives, Fe 2+ ions and green rust, were responsible for Cr(VI) reduction. Furthermore, the presence of Fe 3 O 4 and carbon nitride (g-C 3 N 4 ) improved the stability and reactivity of the nanocomposites.