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 Mossbauer 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 approximate to 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)-O-center dot and O-2(center dot-) radicals participated in the UVA/Fenton degradation process, and (OH)-O-center dot played the dominant role. These morphology-controlled nanomagnetites showed great potential in applications as heterogeneous UVA/Fenton catalysts for effectively treating nonbiodegradable organic pollutants.