A novel synthesis of star-like FeWO4 nanocrystals via a biomolecule-assisted route

Uniform hierarchical star-like ferrous tungstate (FeWO4) is synthesized in a facile manner via a biomolecule-assisted green route without the need for using pre-fabricated templates and reductive agents. l-cysteine in this protocol was not only skillfully useful as a complexing and reducing agent, but also utilized as a structure-directing agent for the formation of star nanostructure. The as-prepared FeWO4 nanostars were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, etc. The results indicate that thickness of the star-like FeWO4 orderly assembled by the nanosheets is ~50 nm. The concentrations of l-cysteine and reaction time play important roles in the assembly of the star-like nanostructure. The morphology of FeWO4 dramatically varies from nanowires (diameter of ~20 nm) to nanoblades with an average thickness of 40 nm, then to the hierarchical star-like FeWO4 according to the changes of experiment conditions. The resulting FeWO4 nanostars with higher order symmetries were phase-pure and possess single crystalline structure. In addition, the star-like FeWO4 shows a small ferromagnetic ordering at low temperature. Moreover, a coordination adsorption and oriented attachment and Ostwald ripening mechanism are proposed for explaining the formation process of star-like FeWO4.