Two-dimensional titania nanosheets

Titania nanosheets is one kind of novel two-dimensional materials with single layer of 0.7 nm thickness, which endows it many special properties different from bulk titania, such as high anisotropy, single crystal property, colloid and polyelectrolyte properties, large specific surface area, high surface energy, quantum size effects, etc. Potential applications can be expected in photon-to-electron conversion, magnetooptical effects, high permittivity devices, electrochemical energy storage, humidity-sensitive sensors, self-cleaning and photocatalysis fields. In this review, the intrinsic properties of titania nanosheets, such as optical absorption, photoluminescence, photon-to-current conversion, photoinduced hydrophilicity and the difference of crystal transformation temperature, are summarized, and the preparation and assembly methods of titania nanosheets are introduced. Then, these new assembled materials and their properties are reviewed in detail by using thin flakes, nanotubes, hollow microspheres and complex films as representations. Afterwards, the modifications of titania nanosheets by doping with impurity ions are also introduced, and the relations between ions doing and properties of titania nanosheets are discussed from three aspects: extending the absorption edge of light, improving electron transfer rate and enhancing magnetooptical response. Finally, the future research trends of titania nanosheets are also suggested.