S.T. Nishanthi

Optimising the crystallinity of anatase TiO2 nanospheres for the degradation of Congo red dye

ABSTRACT Anatase TiO2 nanospheres having a high degradation efficiency are prepared through hydrothermal method employing titanium (IV) isopropoxide as precursor. The effects of hydrothermal temperature on structural, morphological and optical properties of TiO2 nanospheres are investigated. X-ray diffraction (XRD) results show that, the TiO2 nanospheres crystallise in the anatase phase, the tetragonal crystal system. The crystallite size increases with the increase in hydrothermal temperature and the values are in the range of 10–19 nm. On the other hand, the spherical particles evenly distributed on the surface are observed in the scanning electron microscope (SEM) images. The band gap of the nanospheres is determined from the reflectance spectra using Kubelka–Munk function. The band gap energy decreases from 3.189 (2) to 3.023 (5) eV with the increase in hydrothermal temperature. The decrease in band gap values well agree with the XRD results of higher crystallite size and enhanced crystallinity. The removal of Congo red dye under dark condition varies with the hydrothermal temperature and it is maximum for the higher crystallinity anatase TiO2 synthesised at 160 °C having a lower band gap of 3.023 (5) eV. Maximum efficiency of 96.9% and rate constant value of 0.01413 g mg−1 min−1 are observed for the sample hydrothermally synthesised at 160 °C.

Role of water content in anodization of titanium to fabricate TiO 2 nanotubes and its properties

The effect of water content in anodization of Ti foil on photoelectrochemical activity of TiO2 nanotubes fabricated were studied and optimized. The mixed phase of TiO2 was confirmed from X-ray diffraction and their morphological changes with respect to increase in water content were analyzed using High Resolution Scanning Electron Microscope. The optical band gap of TiO2 can be effectively tuned from 3.023(2) to 2.601(7) eV by varying the water content in anodization. The maximum photocurrent density of 2.5 mA/cm2 was observed for the TiO2 sample with higher crystallinity. These results suggest that the higher crystallinity with ordered nanotubes and lesser band gap act as a key role in improving the photoelectrochemical activity of TiO2.

Degradation of methyl orange using bismuth oxide

Bismuth oxide is prepared by a simple chemical route and it crystallizes in the monoclinic crystal system. The measured optical band gap value of 2.694(1) eV supported that the prepared bismuth oxide can be used as a visible light photocatalyst. The degradation property of bismuth oxide is studied using methyl orange as a model pollutant and a degradation of 85% is achieved in 4 h. The kinetics of bismuth oxide is fitted using pseudo first and second order equations.

Synthesis of phase pure BiDyO3 and its structural characterization

Phase pure bismuth dysprosium oxide (BiDyO3) is prepared by means of a simple chemical route by varying calcining temperature. Its homogeneous nature is confirmed from XRD and the photocatalytic degradation exists only for the phase pure form of BiDyO3. The crystallite sizes of BiDyO3 calcined at 500, 600 and 700 °C are 9.9, 14.8 and 15.5 nm respectively and this confirms that the materials are in the form of nanocrystalline. For the phase pure BiDyO3 the degradation percentage is found to be 57% in 4 h.