Vapor-phase hydrothermal(VPH)approaches have been employed to prepare several unique crystalline metal oxide inorganic nanostructures.Compared to the generally used solution-phase hydrothermal(SPH)methods,VPH crystal growth possesses some unique features such as highly localized mass transfer and reagent-vapor-rich reaction atmosphere,which allows direct growth of new nanostructures,transformation between different morphologies and control of dimensional/surface chemical properties of the crystals via intentionally tuning the VPH conditions.The resultant crystalline metal oxide inorganic nanostructures are useful in energy and environmental applications such as sensing,photoelectrocatalysis and photovoltaics.The demonstrated VPH approaches can be extended to the fabrication of novel amorphous or hybrid functional materials.