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Magnetite (Fe3O4) polyhedral nanocrystals have been prepared successfully by a simple solvothermal reaction using a mixture of ethylene glycol (EG) and H2O as the solvent without the addition of any surfactants or templates. Based on SEM and TEM characterization, the products were determined to be 50-facet Fe3O4 nanocrystals, 200-300 nm in diameter, enclosed by {100}, {110}, {111}, and high-index {311} facets. The morphological evolution of 50-facet Fe3O4 polyhedra was studied carefully and in detail by adjusting the reaction parameters such as the reaction temperature, the reaction time, the amount of urea, and the volume ratio of EG to H2O in the solvent. The results indicated that an appropriate EG/H2O ratio in the solvent was crucial for the formation of the polyhedral nanocrystals and when the solvent was fixed, the size of the polyhedral nanocrystals could be tuned in a certain range by changing the amount of urea. A possible growth mechanism involving the aggregation and oriented attachment of Fe3O4 seed nanoparticles is proposed on the basis of time-dependent experiments. [ABSTRACT FROM AUTHOR]

A simple route for the preparation of ZnS-reduced graphene oxide (RGO) composites via a one-pot hydrothermal synthesis is achieved. The chemical composition, morphology and structure of the ZnS-RGO samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption specific surface area analysis (BET) and diffuse reflectance absorption (DRS). The results show that the ZnS nanoparticles were well dispersed on the RGO nanosheets which serve as the ZnS nanocrystal growth support and the morphology controller. It was found that the specific surface area of the ZnS-RGO composites increased with the incorporation of RGO. The ZnS-RGO composites were used as photocatalysts for the degradation of methylene blue (MB) under UV light irradiation. The results show the ZnS-RGO composites exhibited better photocatalytic activity and photodegradation kinetics compared with pure ZnS and commercial TiO2 (P25) which is attributed to the high specific surface area and the hindrance of electron-hole pair recombination of ZnS due to the RGO incorporation. Therefore, the RGO has a positive effect on the ZnS-RGO composite as a photocatalyst. [ABSTRACT FROM AUTHOR]