Solid regulating the electron transfer of ZVAl by ball milling for enhanced para-nitrophenol reduction: Necessity of iron sources

Abstract

Para-nitrophenol (PNP) exhibits high toxicity, carcinogenicity, accumulation capacity and the existence of an electron-absorbing nitro group makes it hard to oxidize but can be reduced easily. Zero-valent aluminum (ZVAl) is an excellent reductant, while its insulation film limits its electron transfer. The oxide film needs to be broken to release the electrons inside ZVAl, and the electron transfer rate after the electron release needs to be controlled to avoid the rapid reaction that leads to the loss of ZVAl activity. Therefore, Fe-ZVAlbm was synthesized by directly one-pot ball milling solid ZVAl, FeSO4·7H2O and Fe3O4 to promote the electron release and regulate the electron transfer. FeSO4·7H2O and Fe3O4 showed splendid synergy for effectively removing 95.6% of PNP unaffected by co-existing ions in a broad pH range (3–11). FeSO4·7H2O with crystal structure could effectively cut the pristine insulation oxide film of ZVAl in the milling process, thus promoting electrons inside the ZVAl release. The conductive Fe3O4 particles embedded onto the surface of ZVAl and the surface-bound Fe(II) contained in Fe3O4 could mediate electron transfer to PNP and regulate the electron transfer rate. The superior electron transfer capacity of Fe-ZVAlbm was presented by the smallest radius of the Nyquist curve. In conclusion, Fe-ZVAlbm is of considerable potential for efficiently reducing nitro-substituted organic compounds, with broader prospects for wastewater treatment.