Effect of calcination temperature on structural and photocatalyst properties of nanofibers prepared from low-cost natural ilmenite mineral by simple hydrothermal method

Titanate nanofibers were synthesized via the hydrothermal method (120 degrees C for 72 h) using natural ilmenite mineral (FeTiO3) as the starting material. The samples were characterized by X-ray diffraction (XRD), X-ray fluorescent (XRF), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) for specific surface area. The nanofibers were 20-90 nm in diameter and 2-7 mu m in length. The as-synthesized nanofibers calcined at 300-400 degrees C showed TiO2 (B) whereas the nanofibers calcined at 500 degrees C revealed a mixture of two phases of TiO2 (B) and anatase. The nanofibers calcined at high temperature of 600-1000 degrees C showed a mixture of tri-crystalline of anatase, rutile, and Fe2O3. The rutile phase increased with increasing calcination temperature. The nanofibers calcined at 300-700 degrees C maintained their structure while the morphology of the nanofibers calcined at 800-1000 degrees C transformed into submicron rod-like structure. This increase of calcination temperature led to the phase transformation from thermodynamically metastable anatase to the most stable form of rutile phase. The crystallite size of prepared samples increased with increasing calcination temperature. Interestingly, with increasing calcination temperature, the absorption edge of the prepared samples shows an obvious shift to visible light region due to the change of crystallite phase and increased crystallite size. Therefore, the band gap energy of the prepared samples became narrower with increasing calcination temperature. Furthermore, the photocatalytic activity of the nanofibers calcined at 400 degrees C for 2 h was found to be not merely higher than those of the commercially available TiO2 nanoparticles powders (P-25, JRC-01, and JRC-03) but also the highest of all the samples in this study. (C) 2013 Elsevier Ltd. All rights reserved.