Controlled Nanophase Development in Photocatalytic Titania

Abstract

Acid catalyzed hydrolysis of titanium butoxide was used to synthesize homogenous titania gels, which were converted to the anatase and rutile polytypes through controlled firing. The mechanism of this phase transformation was investigated by quantitative powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Condensation to titania is a function of annealing time, temperature and atmosphere. In air, calcinations below 600 C favored the formation of anatase, with rutile only appearing at >600 C. However, in situ transformation where titania nanoparticles were treated under vacuum in the TEM required heating at higher temperatures up to 900 C. This is may be due to the formation of surface layers of reduced titanium oxide that passivate and retard the anatase to rutile transformation. Grain growth and specific surface area varied inversely, with especially rapid crystallization observed at and beyond the transformation temperature. Potential photocatalytic activity was identified with ultraviolet-visible (UV-Vis) spectroscopy. A red shift of the absorption edge for nano-titania was observed due to quantum size effects.

Cu-doped TiO2/reduced graphene oxide thin-film photocatalysts: Effect of Cu content upon methylene blue removal in water

“…Inset of Fig. 3c shows 2-D fast Fourier transformation (FFT) of selected nanocrystals, which represents a lattice ϳ structure with d (200) = d (020) = 0.19 nm, Ě ;ϭĎϯͿ = 0.15nm and d (111) = 0.22 nm corresponding to anatase crystal structure [22,23]. This result demonstrated the successful formation of anatase crystalline structure.…”

The effect of rate of hydrolysis on structural and optical properties of the TiO2 nanoparticles prepared by a sol–gel method

“…When annealed at 700°C only the rutile phase exists. The crystallite size was estimated from the Scherrer equation [22][23][24][25] using the XRD line broadening as follows:…”

Activity of phthalocyanine-sensitized TiO2-anatase in photooxidation of sulfite ions

“…From among its three natural polymorphs only rutile and anatase have been considered for wide industrial application. Although rutile has proved thermodynamically more stable, however it is anatase which has displayed better photocatalytic activity and hence has received much more attention as a matrix for diverse catalytic systems than rutile does 1, 4, 6 . The band gap energy of anatase (3.2 eV) falls into the UV range of photonic energy and for this reason ultraviolet irradiation is necessary to (photo)activate its electronic system to create the reactive electron-hole pairs (e -, h + ).…”