Freeze-drying synthesis and characterisation of Na composites of ZnO, TiO2 and ZnTiO3 semiconductor oxides

Abstract

The freeze-drying method of metal oxides synthesis has a number of advantages such as high homogeneity, varying porous structures, morphologies and uniform particle size distribution, etc. Because of these advantages, the binary metal oxides ZnO, TiO2 and ternary metal oxide ZnTiO3 were synthesised by the freeze-drying method. The synthesised materials were characterised by X-ray diffraction (XRD), Fourier transform-infra red spectroscopy (FT-IR), UV-VIS spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). The as-synthesised metal oxides were calcined at different temperatures to study the phase evolution and morphological changes. The crystalline cubic-phase ZnTiO3 (a = 8.3948Å) was obtained on calcination of the precursor at 600 • C, and decomposed to the cubic phase Zn2TiO4 (a = 8.4580Å) and rutile TiO2 (a = 4.5955Å and c = 2.9593Å) at 1000 • C. The band gap of ZnO (3.28-3.10 eV), TiO2 (3.37-2.97 eV) and ZnTiO3 (3.92-3.80 eV) calculated using Tauc's relation was found to vary inversely with calcination temperature and phase transition. Prasad et al. (2010) reported the synthesis of 100 % nanostructured rutile TiO 2 by a combined ultrasoundassisted sol-gel technique. The zinc titanate system is an interesting system, having different polymorphic phases such as cubic defect spinel Zn 2 Ti 3 O 8 , cubic inverse spinel ZnTiO 3 , hexagonal-ilmenite type ZnTiO 3

Formation and Structural Characterization of Spinel‐Phase Zn2TiO4 Synthesized in a High‐Temperature Solution Approach

“…Zn 2 Ti 3 O 8 is a thermodynamically stable compound up to a temperature of 800 °C (or slightly less), above which it transforms sequentially into ZnTiO 3 [13] . Nevertheless, pure ZnTiO 3 is difficult to be prepared, because it can decompose into Zn 2 TiO 4 and TiO 2 at high temperature (>950 °C) [14–16] …”

“…[13] Nevertheless, pure ZnTiO 3 is difficult to be prepared, because it can decompose into Zn 2 TiO 4 and TiO 2 at high temperature (> 950 °C). [14][15][16] Among three zinc titanate compounds, Zn 2 TiO 4 with spinel crystal structure has been shown to possess good chemical stability, thermal conductivity and radiation stability, which can be applied to the photocatalytic degradation of organic compounds, [17,18] catalyst [19] and the solidification treatment of lanthanide oxides waste from nuclear spent fuel. [20,21] Synthesis of Zn 2 TiO 4 based on ceramic have been reported by many authors.…”