MS-1-P-3233 New understanding of the atomic structure and nonstoichiometry of Sc-doped TiO2 photocatalysts by using aberration corrected STEM ARM200CF microscope and EELS spectroscopy

The studies on scandium doped TiO2 photocatalyst nanocrystallites are still limited in the iterature. We select Sc-doped process as an effective method to control the surface structure of TiO2 by generation of defects into TiO2 lattice. Characterization of structures at atomic resolution was performed by aberration-corrected JEM-ARM200CF microscope allows for 68 pm spatial resolution. Z-contrast STEM images were collected using HAADF detector. EELS was acquire atomic-scale maps of the chemical composition and assess the local bonding and Ti valence. This is the first example of a Ti-Sc-O system demonstrated that the substitution of Sc for Ti results in changes in photocatalytic activity due to the preferred occupancy of Sc atoms and its effects on the anatase lattice. The changes of both the lattice parameters and surface morphology are related to the chemical bonding between Ti and Sc cations and oxygen atoms, and species formed at the surface with respect to oxygen deficiencies.The highest activity was observed in TiO2-Sc 4.18 at.%. The photocatalytic activity of the Sc doped TiO2 strongly depends on Sc concentration and particle size of both the dopant ion and TiO2 matrix. A general view of the Sc-doped anatase is shown in Fig. 1. The well-known spherical morphology of TiO2 is established. Detailed atomic scale analysis performed with STEM-HAADF detector shows composites with core-shell structure (Fig.2a). High resolution Z-contrast images demonstrates that the scandium ion dispersed into TiO2 nanoparticle and its concentration in the shell regions is higher and formed scandium-rich regions where Sc3+ replace Ti3+ and mixed oxygen vacancy generated composite (Ti3+xTi4+1-x)O2-x is developed. Therefore, the Sc ion can be caused defects by introducing oxygen vacancies in the lattice of TiO2. Two different crystallographic regions can be recognized based on the intensity and the atomic column symmetry. The border region has much larger intensity. This contrast is explained mainly by the effect of the strain field presented in the TiO2@Sc interface (Fig.2b,c and Fig. 3.). HAADF find out that the lattice parameters of the doped TiO2 samples begin to be larger than pure TiO2. We suppose that during nano-crystal growth, the method by which solutions of reacting components are mixed and the intensity of their stirring can influence the precipitation and the physical characteristics of the product. The precipitation of Sc-doped TiO2 results from mixing of two liquids on microscale level. The mixture consists of entirely segregated parts with different local concentration. In such an way a molecular diffusion occurs to form crystals where the inner TiO2 core has a different composition from the outer shell