SCANDIUM DOPED TiO₂ NANOPARTICLES: MICROSTRUCTURE AND PHYSICAL PROPERTIES

During the past few decades, considerable efforts were put for nanomaterials` fabrication exhibiting unique chemical and physical properties. Numerous studies were conducted in order to improve photocatalytic efficiency of TiO₂ nanoparticles.

The goal of this work was to develop an easy synthetic approach that would permit synthesis of ultrafine TiO₂ anatase, quantum size 5 – 6 nm particles, self-ordered into spherical clusters. Since the ion radius of scandium ion is the smallest among the rare earth elements and closer to that of titanium, one could expect that Sc is capable to make solid solution with TiO₂. 4 at.% Sc³⁺ is enough to stabilize the tetragonal structures of anatase in a mesoporous structure. Doping with larger Sc³⁺cation (r_Sc = 0.745 Å) than Ti⁴⁺ (r_Ti= 0.605 Å) caused high concentration of point defects (distortion of crystal lattice) by the formation of mixed valence states Ti⁴⁺/Ti³⁺ (sub-stoichiometric Ti₃O₅ oxide). Variation in surface species Ti³⁺, Ti⁴⁺, O^2-, oxygen vacancies, and OH group was studied using X-ray photon spectroscopy (XPS). Joined small-angle X-ray and neutron scattering (SAXS/SANS), High resolution microscopy, FTIR, UV/Vis, NMR, BET were applied in order to investigate the microstructure of these samples and their physical properties. Grain boundary defects, determined by HRTEM analysis, and Ti₃O₅ nanocrystals (NCs) capped the surface of TiO₂ clusters were found.

In-situ thermal treatments were applied to the Sc-doped TiO₂ samples, while x-ray diffraction patterns were collected for each temperature up to 1200ºC. Rietveld analysis of these XRD patterns showed that only anatase exists at 25-875ºC. At 900ºC rutile starts to appear and anatase to disappear which was totally vanished at 1200ºC. At 975 - 1200ºC temperature range also Sc₂TiO₅ (3-5%) was found.