Spectroscopic Investigation on Sol Gel Derived TiO₂ Nanoparticles

Abstract

Abstract. TiO 2 nanoparticles were synthesized by sol-gel method from titanium tetra isopropoxide. Influence of heat treatment on structural and morphological properties of TiO 2 nanoparticles was investigated by XRD and SEM. Spectral properties of the nanoparticles were investigated using FTIR, Raman spectroscopy, PL spectroscopy and UV-visible absorption spectroscopy. XRD analysis revealed the formation of mixed anatase and ruitle phase in the synthesized powder at 550 o C and existence of only rutile phase at 750 and 900 o C. The lattice parameters, crystallite sizes, volume of the unit cell, density and surface area of TiO 2 nanoparticles were determined from XRD analysis. SEM analysis showed that the prepared nanoparticles were in the nano regime, nearly spherical and larger agglomerated at lower temperature. EDX analysis showed that the TiO 2 composition obtained was near stoichiometric at lower temperature and the proportion of oxygen vacancy increased with the increase in temperature. The presence of Ti-O and Ti-O-Ti bonds was confirmed by FTIR spectra. PL spectroscopy showed that the change in surface states and presence of anatase and rutile phases of TiO 2 were also responsible for exhibiting the change in PL intensity. UV-visible absorption spectra showed the shifting of absorption edge towards the higher wavelength with the increase in temperature while the corresponding energy band gap of semiconductor nanoparticles decreased. Change in Raman spectra with the increase in temperature was observed due to anatase to rutile phase transformation and with the increase in the particle size.Keywords: TiO 2 nanopowder, sol-gel, annealing, spectroscopic properties. IntroductionTitania nanoparticles have important applications in the field of optical devices, sensor and photocatalysis [1,2]. These nanoparticles have different electrical, optical and magnetic properties compared to their bulk counterparts due to large surface to volume ratios and quantum size effect [3]. There are several factors in determining the important properties like, particle size, crystallinity and morphology that affect the performance of TiO 2 in applications [4][5][6]. TiO 2 as a wide indirect band gap n-type semiconductor and generally exist in the three polymorphs of TiO 2 are anatase (I4/amd), rutile (P42/mnm) and brookite (Pcab). Brookite exists in an orthorhombic structure while anatase and rutile both possess tetragonal unit cells. Among these, anatase is metastable at lower temperature and has excellent chemical and physical properties for environmental purification, although rutile is the more stable phase from thermodynamic point of view. The phase composition has significant effect on the properties and performance of nano TiO 2 and therefore it is desirable to control the transformation to develop a particular phase or phase mixture subsequent to thermal treatment. The phase transformation depends on the growth process affected by defect concentration, grain boundary concentration and particle packing as well [7][8][9]. ...

Effects of Ti-precursor concentration and annealing temperature on structural and morphological properties of TiO2 nano-aerogels synthesized in supercritical ethanol

“…The crystallites size also increases with increasing annealing temperature. This increase may be due to the fact that the crystallite growths can be related to the removal of oxygen ions migration towards the outer side of the particles [45]. It is well known that anatase is a metastable phase and its conversion to rutile involves an irreversible collapse of the anatase structure.…”