Insights into the roles of organic coating in tuning the defect chemistry of monodisperse TiO2 nanocrystals for tailored properties

This work initiated a systematic study on the chemical nature of organic coating for monodispersed nanoparticles and its impact on the defect chemistry and the relevant properties. Monodispersed TiO2 nanoparticles were prepared by a nonhydrolytic sol-gel reaction, which showed features of uniform diameter distribution around 5.2 nm, high crystallinity, and single anatase structure. These nanoparticles were terminated by oleate-related molecules, which stabilized the surface oxygen vacancies and further generated intense photoluminescence and co-existence of ferromagnetism and diamagnetism. After removal of organic coating, the nanoparticles became highly aggregated with no apparent changes in particle size, while the oxygen vacancy concentration was significantly reduced, as followed by energy position shift towards the deeper-levels which promoted the separation of photogenerated electrons and holes for improved photocatalytic activity. The results reported here are fundamentally important, which may be extended to comprehend the size-dependent defects and structure-property correlations of monodispersed nanoparticles for applications.