Zeolite supported Fe/Ni bimetallic nanoparticles for simultaneous removal of nitrate and phosphate: Synergistic effect and mechanism

Abstract

Excessive nutrients (N and P) are among the most concerned pollutants in surface and ground waters. Herein, we report nanoscale zero-valent iron/nickel supported on zeolite (Z-Fe/Ni) for simultaneous removal of nitrate and phosphate from aqueous solution. The synergistic effect between zeolite and Fe/Ni bimetallic nanoparticles, as well as the removal mechanism was investigated systematically. The characterization by BET, TEM and XPS demonstrated that nanoscale zero-valent iron/nickel was successfully loaded onto zeolite, and Z-Fe/Ni exhibited larger specific surface area and more uniform dispersion than unsupported Nano-Fe/Ni. XRD, FTIR and XPS analysis revealed that the Fe0 supported on the surface of zeolite were protected from oxidization. Batch experiments showed that nitrate reduction by Z-Fe/Ni was not sensitive to initial solution pH, while phosphate removal was affected. Moreover, Z-Fe/Ni displayed higher equivalent N2 selectivity (85.5%) and less ammonium release than that of Nano-Fe/Ni, which was mainly attributed to the selective ion-exchange of NH4+ by zeolite, indicating the significant synergistic effect of the combination of zeolite and Nano-Fe/Ni. The influence of one pollutant on the removal of the other manifested that the presence of phosphate inhibited nitrate reduction through forming Fe-P complex, while the phosphate removal was promoted by the present nitrate via accelerating corrosion of Fe. Nitrate reduction pathway identification and FTIR, XPS analysis confirmed that reduction and complexation were the dominant mechanism for nitrate and phosphate, respectively.