Graphitic carbon nitride (g-C3N4) loaded nanoscale zero-valent iron (nZVI) composites for enhanced hexavalent chromium removal: The role of g-C3N4, performance and mechanistic study

To enhance the stability of nanoscale zero-valent iron (nZVI) and prevent its oxidation, graphitic carbon nitride (g-C3N4) was incorporated onto the nZVI surface, resulting in a composite material denoted as g-C3N4@nZVI. Characterization techniques, including SEM, XRD, FT-IR and TGA confirmed the successful synthesis of the composite and demonstrated a marked improvement in its stability. The experimental findings indicated that at an initial concentration of 30 mg/L with a pH of 5, and under visible light irradiation, the composite material gC3N4@nZVI, with a mass ratio of g-C3N4 to Fe of 1.0:1, demonstrated superior Cr(VI) removal efficiency compared to either g-C3N4 or nZVI alone. Specifically, the Cr(VI) removal rate was enhanced by 89.67 % and 38.28 %, respectively, over g-C3N4 and nZVI. The outcomes of UV-vis, EIS and antioxidant assays revealed that iron-induced g-C3N4 facilitated electron generation, with an increased participation of Fe2+ in the reduction of Cr (VI). The slower oxidation rate of nZVI augmented the Cr(VI) removal efficiency. After 28 days, the Cr(VI) removal rate remained above 70 %, and it sustained this level after three cycles. Collectively, the significant improvement in Cr(VI) removal was attributed to the synergistic interaction between nZVI and g-C3N4. This study provides novel insights into the modification of nZVI to enhance Cr(VI) removal efficiency.