5CB LIQUID CRYSTAL AS A SPECIFIC PROBE FOR SURFACE STUDIES OF METAL-DOPED TIO2 (ANATASE) NANOPARTICLES

Abstract

Metal-doped Men+-TiO2 (where Me is Cu+, Mn2+, Cr2+, Co2+, Ni2+, Fe3+) anatase powders and heterogeneous systems Men+-TiO2-4-pentyl-4′-cyanobiphenyl have been studied by FTIR spectroscopy method. TiO2 samples have been produced by thermal hydrolysis of titanium chloride and as their spectroscopic data revealed, have different types of surface active centers and the amount of hydroxyl and hydrate covering. Doped metal cations increase a variety of possible active centers, disturbing surface OH-groups by coordination or ionic bonding. 5CB molecules, approaching TiO2 surface, displace adsorbed water molecules and can create hydrogen bonds of -CN…HO-Ti≡ and π-electrons…HO-Ti≡ types. The influence of metal cations is a polarizing effect on 5CB molecules, which increases in a following row Cu+ < Mn2+ < Cr2+ < Co2+ < Ni2+ < Fe2+. This is in a perfect agreement with the polarizing activity of these cations. At that 5CB molecules change their orientation and possess some deformations, which is confirmed by the corresponding changes in spectral parameters of 5CB deformation modes.