Enhanced Selective Nitrate-to-Nitrogen Reduction by Aerosol-Assisted Iron-Carbon Composites: Insights into the Key Factors

In this study, an aerosol-assisted Fe0/C (carbon supported zero-valent iron) composite was prepared and evaluated, which could effectively remove nitrate and exhibit high nitrogen selectivity. The results show that the selectivity of nitrogen for freshly prepared Fe0/C composites could reach 52.2% when pH at 7, compared to that of 7.7% for traditional nZVI. Meanwhile, the removal efficiency of nitrate was slightly increased from 63.5% to 69.9%. Furthermore, a variety of methods such as SEM, TEM, XRD, XPS, BET, FTIR and TGA were used to characterize the Fe0/C composites before and after reaction. Hence, the following key factors were determined for the effective conversion from nitrate to nitrogen: the surface of zero valent iron particle should be protected from oxidation and its genuine characteristics are well retained; the reaction should be controlled under an anaerobic condition; and the carbon as the carrier to support iron particles is very important; lower initial pH favors nitrogen generation. Various materials including aged Fe0/C composites, Fe0/SiO2 (SiO2 supported zero-valent iron) composites and nZVI particles in the deoxygenated and oxygenated systems were assessed for comparison.