Microwave-Assisted Synthesis of Fe3O4 Nanocrystals with Predominantly Exposed Facets and Their Heterogeneous UVA/Fenton Catalytic Activity.

Fe3O4 nanocrystals with five different morphologies (i.e., nanospheres, nanorods, nanocubes, nano-octahedrons, and nanoplates) were acquired using a simple, efficient, and economic microwave-assisted oxidation technique. The microstructure, morphology, predominant exposed facets, and iron atom local environment of Fe3O4 were revealed by powder X-ray diffraction (PXRD), scanning transmission electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometer (XPS), and Mössbauer spectrum. We demonstrated that the heterogeneous UVA/Fenton catalytic activities of Fe3O4 nanocrystals are morphology/facets dependent. Under UVA irradiation, the catalytic activity of the as-prepared Fe3O4 was in the sequence of nanospheres > nanoplates > nano-octahedrons ≈ nanocubes > nanorods > nano-octahedrons (by coprecipitation). The dominating factor for the catalytic performance was the particle size and BET specific surface area; moreover, the exposed {111} facets, which contained more Fe2+ species, on the nanocrystal surface led to a stronger UVA/Fenton catalytic activity. Both •OH and O2•- radicals participated in the UVA/Fenton degradation process, and •OH played the dominant role. These morphology-controlled nanomagnetites showed great potential in applications as heterogeneous UVA/Fenton catalysts for effectively treating nonbiodegradable organic pollutants.