On the Sol-gel Synthesis and Characterization of Titanium Oxide Nanoparticles
- PDF / 369,387 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 86 Downloads / 233 Views
On the Sol-gel Synthesis and Characterization of Titanium Oxide Nanoparticles Varun Chaudhary, Amit K. Srivastava and Jitendra Kumar Materials Science Programme, Indian Institute of Technology Kanpur, Kanpur, India Email- [email protected] ABSTRACT TiO2 nanoparticles have been prepared by sol-gel process using titanium isopropoxide as a precursor with ethanol and water as solvents. The synthesis involves gel formation, digestion for 24h, drying at 100oC for 10h, and calcination in air at 500-800oC for 2h. The resulting powder has been studied with respect to phase(s), morphology, optical absorption and photo luminescence (PL) behaviour. The calcination of dried sol-gel product at 500oC for 2h leads to formation of anatase phase that possesses a tetragonal structure (a = 3.785 Å, c = 9.514 Å, Z = 4), average crystallite size ~ 11 nm and band gap of 3.34 eV. Further, increasing the time (t) of calcination causes crystallite growth that follows the relation d = Į – ȕ exp (-t/IJ), Į = 18.1 nm, ȕ = 9.6 nm and IJ = 6.9h. However, calcination of sol-gel product at 800oC for 2h gives rise to a rutile phase (tetragonal a = 4.593Å, c = 2.959Å, Z = 2), average crystallite size ~ 25 nm and band gap of 3.02 eV. The anatase phase exhibits strong PL emission peaks (excitation wavelength 405 nm) at 2.06 and 1.99 eV due to defect levels within the energy band gap. This observation has been attributed to finite size effects occurring in nanoparticles.
INTRODUCTION Titanium dioxide (TiO2) exhibits unusual structural, optical, electronic, magnetic and chemical properties [1, 2]. As a consequence, it has found wide applications in pigments, UV protection creams, photo-catalysis, solar cells, water and air purification, synthesis of inorganic membranes, etc. [3, 4]. Its important phases include anatase, rutile (both tetragonal, described by sharing of (TiO6)2- octahedra), brookite (orthorombic), and a recently discovered oxygen deficient Ȝ-Ti3O5, having a monoclinic crystal structure and photo-reversible characteristics [5, 6]. In bulk, anatase and brooklite are less stable and undergo transition to rutile phase which remains thermodynamically stable under atmospheric pressure up to the melting point (1840oC). The transformation to rutile phase is dependent on several parameters such as particle size, temperature and the environment. TiO2 thin films have found application in dye-sensitized solar cells (DSSC) because of their interconnected pore networks and a large surface area, which allows sufficient dye adsorption and efficient light harvesting. Hence, the performance of such cells depends on the nature of porous structure and average particle size besides the phase. The conversion efficiency of ~11% or more is already attained in the laboratory [7]. However, the commercial devices have yet to reach at that level. Cell stability is another issue requiring attention. One way to improve the efficiency and stability of DSSCs may be through the exploitation of electrodes with TiO2 nanoparticles of superior characteristics [8]. The shortcircuit
Data Loading...
