Evonik Aeroxide P25 (formerly Degussa P25) is a flame-made multiphasic TiO2 nanoparticles containing anatase
and rutile, as well as a small amount of amorphous TiO2. The past decades have witnessed the wide applications
of P25 as a benchmark material for studying photocatalytic mechanism, materials and process. However, controversy remains regarding the microstructure of anatase and rutile: do they interwoven forming heterojunction
structure or exist individually? To clarify it, we selected a medium alkaline, LiOH to erode bare P25 under a mild
hydrothermal condition. Since rutile presents much higher resistances towards dissolution by LiOH than anatase,
it is reasonable to find during hydrothermal reaction that the ratio of anatase to rutile (A/R) gradually decrease
if they exist individually. Reversely, the A/R value gradually increases at the beginning of the hydrothermal
reaction, implying that rutile shows high activity towards dissolution and phase transformation to lithium titanate. As calculated, around 15% rutile nanoparticles more likely exist on the surface of anatase with the
formation of a heterojunction structure, although isolated nanoparticles with sole rutile phase coexist. In addition to XRD analysis, TEM measurement shows that the Moiré fringes frequently present, which further
manifests that some anatase particles are covered with rutile clusters or thin overlayers