Template-free synthesis of 3D Nb(3)O(7)F hierarchical nanostructures and enhanced photocatalytic activities.

Single-crystalline niobium oxide fluoride (Nb(3)O(7)F) hierarchical nanostructures are firstly prepared via a facile hydrothermal method without using any template or surfactant. The results of scanning electron microscopy and transmission electron microscopy showed that the hierarchical morphology of Nb(3)O(7)F could be effectively controlled by adjusting the reaction time. Ultraviolet-visible spectra showed that such nanostructures have a narrow absorption peak at around 400 nm compared to Nb(2)O(5). Based on the first-principles plane-wave ultrasoft pseudo potential (USPP) method, the crystal structures of Nb(3)O(7)F was optimally calculated for the total density of states (TDOS) and the partial density of states (PDOS) of Nb, O and F atoms. According to the observations of architectures formation, a possible growth mechanism was proposed to explain the transformation of nanoparticles to hierarchical nanostructures via an Ostwald ripening mechanism followed by self-assembly. In particular, the excellent photocatalytic activity of the Nb(3)O(7)F hierarchical nanostructures was confirmed by photodegradation of methylene blue, methyl orange and rhodamine B molecules.