Materials with intricate nanostructures display fascinating properties,which have inspired extensive research on the synthesis of materials with controlled structures.Here we investigated the properties of superstructures of TiO2 to understand the inter-relationship between structural ordering and photocatalytic performance.The nanoplate anatase TiO2 mesocrystals were newly synthesized by a topotactic structural transformation.The TiO2 mesocrystals displayed the superstructure of crystallographically ordered alignment of anatase TiO2 nanocrystals with high surface area and large high-energy surface {001} planes exposed.The photoconductive atomic force microscopy and time-resolved diffuse reflectance spectroscopy were utilized to determine the charge transport properties of TiO2 mesocrystals,and their features were highlighted by a comparison with reference TiO2 samples,for example,anatase TiO2 nanocrystals with similar surface area and single crystal structure.Consequently,it was found that such a superstructure of TiO2 could enhance charge separation and had long-lived charges,thereby exhibiting increased photoconductivity and photocatalytic activity.Next,we investigated the charge transport in the nanocomposites containing plate-like anatase TiO2 mesocrystal superstructures and noble metal(Au,Pt)nanoparticles.These novel metal nanoparticles were photodeposited on the edge of TiO2 mesocrystals.Single-molecule fluorescence spectroscopy measurements on a single particle directly revealed that most of the photogenerated electrons could migrate from the dominant surface to the edge of the TiO2 mesocrystal with the reduction reactions mainly occurring at its lateral surfaces containing {101} facets.The loading of metal nanoparticles on the superstructure of TiO2 was found to greatly improve the photogenerated charge separation efficiency allowing significant enhancement of the photocatalytic reaction rate in organic degradation reactions.These features allowed reduced consumption(ca.10%of that of typical TiO2 nanocrystal samples)of the Au or Pt loading on the TiO2 mesocrystal while maintaining the same photocatalytic activity.