Synchrotron small angle x-ray scattering study of dye-sensitized/-unsensitized TiO2 nanoparticle colloidal solution

The wide-gap semiconductor TiO2 nanoparticles with and without dye sensitization have been studied by small angle x-ray scattering using synchrotron radiation. Surface properties of the colloidal TiO2 nanoparticles have been analysed in terms of the surface fractal dimensions (Ds), showing that Ds changes from 3.25 to 2.34 when TiO2 nanoparticles are sensitized by ATRA (all-trans-retinoic acid), which reveals that the surface of the particles become relatively smooth after dye sensitization. The size distribution of gyration radius of TiO2 nanoparticles in the colloids M(Rg) has been successfully determined by the Shull–Roess method. The main peak of M(Rg) for the unsensitized TiO2 colloid is located at 2.1nm, corresponding to a spherical diameter of 5.4nm and this value for the ATRA sensitized TiO2 increases to 2.4nm, indicating a spherical diameter of 6.4nm. Such a size enlargement of TiO2 nanoparticles suggests that there is a coating of ATRA on the TiO2 surface, supporting the view that a monolayer of the dye has been attached to the surface of the TiO2 nanoparticle.