M. Malligavathy

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.

Effect of anodization time on the growth of twinned pyramid crystals of bismite from polyhedral bismuth particle by facile electrolysis-based oxidation

ABSTRACT Nanostructured bismite films were fabricated by both thermal oxidation and electrochemical anodization of Bi film in NaOH aqueous electrolyte. Pure phase of α-bismite was obtained by the thermal oxidation technique. Pure-phase α and β bismites were successfully prepared by varying the anodization time. Truncated polyhedral aggregates of bismuth particles were converted to twinned pyramids particles having nanoscale tips with increase in anodization time. The crystallite size increased with anodization time from 43 nm to 79 nm. The band gap value lowered from 2.835(2) eV to 2.422(1) eV with anodization time and this is in agreement with the increase in crystallite size obtained from XRD. The shift in the absorption edge to higher wavelength with anodization time was attributed to the smoothening of surface and grain growth.

Phase Purity Analysis and Optical Studies of Bi2O3 Nanoparticles Suitable for Photocatalytic Activity

Bismuth oxide was prepared using hydrothermal route and the effect of pH on the phase of Bi2O3 reported. Phase pure α-Bi2O3 was prepared at the pH of 13 and its phase purity was confirmed from the X-ray diffraction pattern. At the pH of 10, 11 and 12 the hydrothermal synthesis yields Bi(OH)3, (α, γ-Bi2O3) & Bi2O4 and mixture of α-Bi2O3 & Bi2O4, respectively. The optical band gaps were calculated from reflectance spectra using the Kubelka–Munk relation and the values decrease from 3.050(3) to 2.686(3) eV with the increase in pH value. Photoluminescence intensity decrease with the increase of pH value indicated the increase in the charge separation efficiency. In the application point of view, the photocatalytic activity of the samples was evaluated for methyl orange and among the four samples, α-Bi2O3 degraded 67% within 4h. The degradation of dye was analyzed using pseudo first-order kinetics and the rate constant value was 0.0045(3) min−1 with the correlation coefficient of 0.983.

Structural, morphological, and optical properties of tin(IV) oxide nanoparticles synthesized using Camellia sinensis extract: a green approach

Tin oxide (SnO2) nanoparticles were cost-effectively synthesized using nontoxic chemicals and green tea (Camellia sinensis) extract via a green synthesis method. The structural properties of the obtained nanoparticles were studied using X-ray diffraction, which indicated that the crystallite size was less than 20 nm. The particle size and morphology of the nanoparticles were analyzed using scanning electron microscopy and transmission electron microscopy. The morphological analysis revealed agglomerated spherical nanoparticles with sizes varying from 5 to 30 nm. The optical properties of the nanoparticles’ band gap were characterized using diffuse reflectance spectroscopy. The band gap was found to decrease with increasing annealing temperature. The O vacancy defects were analyzed using photoluminescence spectroscopy. The increase in the crystallite size, decreasing band gap, and the increasing intensities of the UV and visible emission peaks indicated that the green-synthesized SnO2 may play future important roles in catalysis and optoelectronic devices.