The well-known physical phenomenon Ostwald ripening in crystal growth has been widely employed in template-free fabrication of hollow inorganic nanostructures in recent years. Nevertheless, all reported works so far are limited only to stoichiometric phase-pure solids. In this work we describe the first investigation of doped (nonstoichiometric) materials using Ostwald ripening as a means of creating interior space. In particular, we chose the xSnO2-(1 - x)TiO2 binary system to establish preparative principles for this approach in synthesis of structurally and compositionally complex nanomaterials. In this study, uniform Sn-doped TiO2 nanospheres with hollow interiors in 100% morphological yield have been prepared with an aqueous inorganic route under hydrothermal conditions. Furthermore, our structural and surface analyses indicate that Sn4+ ions can be introduced linearly into TiO2, and preferred structural phase(s) can also be attained (e.g., either anatase or rutile, or their mixtures). Fluoride anions of starting reagents are adsorbed on the surface sites of oxygen. The resultant anion overlayer may contribute to stabilization of surface and creation of repulsive interaction among the freestanding nanospheres. On the basis of these findings, we demonstrate that Ostwald ripening can now be employed as a general hollowing approach to architect interior spaces for both simple and complex nanostructures.

Reactor core: Hollow core–shell Au–TiO2 nanocomposites can be prepared by a wet chemical method to form reactors that contain a catalyst core with a shell that is permeable to reactants. The core can be enlarged, and modification of the synthesis produces flowerlike nanostructures (see picture). Catalytic reactions in both the gaseous and liquid phase can be conducted in this type of photosensitized metal–semiconductor nanoreactor.

Recent advances in the electrical conductivity, intrinsic activity and morphology design of transition-metal-oxide-based oxygen reduction catalysts are summarized.

Efficient photocatalytic nanocrystals with high-ratio exposure of active facets have aroused a great number of research interests in recent years. However, most preparations of such materials need the addition of special capping agents (like surfactants) or harsh reaction conditions (such as hydrothermal reactions). In this work, a controllable synthesis of BiOBr nanosheets with a thickness from 9 nm to 32 nm was easily achieved in a hydrolysis system through adjusting temperature and solvent, without adding any surfactant or capping agents. As the thickness of the nanosheets decreases from 32 nm to 9 nm, the ratio of exposed {001} facets, the active photocatalysis facets in BiOBr crystals, increases from 83% to 94%, along with an increased photocatalytic efficiency over rhodamine B (RhB) under visible-light.Various methods such as SEM, TEM, AFM, DRS and Raman spectroscopy were used to fully characterize the as-obtained BiOBr nanosheets. More importantly, the obtained BiOBr nanosheets exhibit a selective visible-light photocatalytic behavior as the activity over RhB is much higher than that over Methyl Orange (MO) or Methylene Blue (MB). This phenomenon was studied with in situ electron paramagnetic resonance (EPR) measurements and the potential mechanism was explored.