Single-crystalline Fe7S8/Fe3O4 coated zero-valent iron synthesized with vacuum chemical vapor deposition technique: Enhanced reductive, oxidative and photocatalytic activity for water purification

Well-defined core/shell type single crystalline Fe7S8/Fe3O4 coated alpha-Fe hybrids (Fe7S8/Fe3O4@Fe) are synthesized with vacuum chemical vapor deposition (CVD) technique. The CVD process triggers conversion of naturally formed Fe3O4 layer on the surface of commercial Fe nanoparticles from amorphous into single crystalline phase. The Fe7S8/Fe3O4 coat promotes the surface affinity of dissolved oxygen and targets and rapidly transfers electrons from the Fe core to targets, which decreases water splitting on Fe7S8/Fe3O4@Fe surface and endows Fe7S8/Fe3O4@Fe with ultra-strong reducibility and improved oxidative ability under different conditions. Different with the sulfurized ZVI prepared with hydrothermal or solvothermal method, the increase of reaction solution pH is retarded due to the relieved water splitting instead of releasing H+ via oxidation of S-2(-)/S-2(2-) on the Fe7S8 coat. The cooperation of Fe7S8 with Fe3O4 and alpha-Fe not only improves the anti-oxidation ability of Fe7S8 coating but also broadens its band gap. By using Fe7S8/Fe3O4@Fe nanohybrids as photocatalysts, light irradiation accelerates the degradation of organic pollutants combined with enhanced mineralization efficiency. The Fe7S8/Fe3O4@Fe exhibits good performance when it is utilized to treat the influent from a municipal sewage treatment plant upon air aeration or under visible light and solar light irradiation.

Automated summary

The synthesized Fe7S8/Fe3O4@Fe nanohybrids exhibit strong reducibility and improved oxidative ability. Unlike sulfurized ZVI prepared with hydrothermal or solvothermal methods, the Fe7S8 coating retards the increase of solution pH and enhances the efficiency of photocatalytic degradation of organic pollutants.