An investigation on the influence of hydrolysis ratio and base type on the characterization of synthesised nano-TiO2 by using sol–gel method

Abstract The titanium oxide (TiO2) nanoparticles were synthesized through hydrolysis-condensation of Titanium (IV) n-butoxide [Ti(OBun)4] by using a sol–gel-based hydrothermal method, also called the modified sol–gel method. In the synthesis of TiO2 particles, the effect of water content and base types on the structure and surface properties of the particles was investigated. At the lowest water ratio (r = 1, OTiO2-1), the formation of the anatase crystal phase was not complete, and at the water ratios above the stoichiometric ratio (r = 25 and 50, OTiO2-25, and OTiO2-50), remains from the residual of the brookite phase. The crystallite sizes of OTiO2-1, OTiO2-2, OTiO2-4, OTiO2-10, OTiO2-25, and OTiO2-50 coded TiO2 crystals that calculated by the Scherrer equation were 0,15 nm; 3.71 nm; 3.73 nm; 5.66 nm; 5.00 nm; 5,19 nm, respectively. In addition, transmission electron microscope (TEM) images of particles have been taken for comparison in order to confirm the calculated crystallite size from the Scherrer formula and obtained primary and secondary sizes from Zetasizer Nano. The optical absorption edge shifts to the higher energy region, that is, to a lower wavelength, with decreasing particle size. As it is expected, for OTiO2-2 and OTiO2-4, the absorption limits shifted to lower wavelength with decreasing crystallite size. The values of optical band gap energy confirm the crystal sizes obtained from the XRD analysis as it is associated with the reduction of crystallinity size, which determines the quantum size effect of the high bandgap. TiO2 particles prepared using different bases were obtained in anatase form (except OTiO2-TMA), provided that the water ratio remains constant. The crystallite sizes of the particles were higher than those in an acidic medium, and the smallest OTiO2-NH3 was obtained when their bases were compared to each other. When the absorption edges are examined according to the UV–Vis spectra, the red shift of the particles synthesized in the basic medium was more pronounced. While the band gap energies exhibited higher behavior in accordance with the size compared to the particles obtained in the acidic environment, it was determined that OTiO2-TMA had the highest band gap energy when compared with each other according to the base types. When SEM images were examined, spherical smooth particles were obtained as a result of using ammonia, which has less basic strength. Graphical abstract