Solid State Phenomena Vol. 162

Abstract: The carbon modified n-type titanium oxide (CM-n-TiO2) thin films were synthesized by flame oxidation of Ti metal sheets both flat and grooved and also by using combination of spray pyrolysis and flame oxidation of flat surface. Also undoped reference n-TiO2samples were also synthesized in an electric oven for comparison. Photoresponse of CM-n-TiO2 and n-TiO2 were evaluated by measuring the rates of water splitting to hydrogen and oxygen, in terms of observed photocurrent densities. Under the white light illumination of intensity of 100 mW cm-2 from the xenon lamp the photocurrent densities were found to be 1.60, 9.17, 11.44 and 14.68 mA cm-2 for optimized oven made n-TiO2 (sample1), flame made on flat surface (sample 2), on grooved surface (sample 3) and spray pyrolysis-flame made CM-n-TiO2 (sample 4) thin films at 0.477 V, 0.240 V, 0.242 V and 0.215 V biases respectively. The corresponding maximum photoconversion efficiencies for these thin films were found to be 1.2 %, 9.08 %, 11.31 % and 14.04 % for samples 1-4 respectively. Under monochromatic light illumination from the xenon lamp the maximum photoconversion efficiencies for samples 1-4 were found to be 0.94 %, 8.86 %, 11.16 % and 13.79 % respectively. However, under actual natural global AM 1.5 sunlight illumination of 1 sun, the maximum photoconversion efficiencies reduced to 0.67 %, 5.63 %, 7.62 % and 12.26 % for samples 1, 2, 4 and 3 respectively. These values compared well with those found under monochromatic light illumination from the xenon lamp. The increasing efficiencies were found consistent with lowering of band gaps from 2.9 eV for sample 1 to 2.65 eV and generation of mid-gap band at 1.6 eV for both samples 2 and 3 and 1.4 eV above the valence band for sample 4. Carbon contents were found to be 0.0, 17.60, 19.38 and 23.23 atom % for samples 1, 2, 3 and 4 respectively.

Abstract: A comprehensive analysis of structural-reactivity relations on TiO2 nanocrystals is presented. Using an interplay between TEM, X-ray diffraction and vibrational spectroscopy of well-defined anatase and rutile TiO2 nanocrystals correlations between the adsorbate structure of formic acid and the corresponding photo-induced decomposition rate are described. It is demonstrated that the detailed bonding configuration determines the decomposition rate. Generalizations and implications of the findings are discussed.

Abstract: This paper presents a review of the work published by the authors on the synthesis, characterization and evaluation of the photocatalytic activity of TiO2/SiO2 materials. The use of titania-silica mixed oxides photocatalysts is proposed basically as a process improvement to overcome the difficulties of recovering titania from the slurries after the photocatalytic treatment of contaminated waters. To understand the mechanism governing the photocatalytic activity of these materials, several titania-silica photocatalysts have been prepared through a sol-gel method that allows controlling the main variables to obtain materials with different textural properties, degree of titania incorporation, dispersion of the photoactive phase and crystallinity of titanium dioxide. The samples have been characterized in depth, looking for correlations between the main physicochemical properties (TiO2 crystallite size, band gap energy and titania surface area) and the activity shown in the photocatalytic oxidation of cyanide, selected as model pollutant. The results suggest that the photocatalytic activity is strongly influenced by the quality of the titania crystal network, which in turn is improved by the use of a hydrothermal crystallization procedure. Additionally, the evaluation of the fraction of the total surface area corresponding to titania is mandatory for comparing the catalytic activity of different materials in processes in which titanium dioxide is the only phase catalytically active and silica behaves as an inert support.

Abstract: Since the beginning of life on earth, the environment has been polluted by waste, both natural as well as synthetic (man-made). In the case of natural waste however, the environment by itself controls the effect of contamination. But in the case of synthetic materials, the pollution is higher even in trace concentration and this may go on accumulating, leading to disastrous effects on the environment and ecology. Industrial wastes containing heavy metals and pesticide residues fall in this category. The major point sources of pesticide pollution are wastewater from agricultural industries and pesticide manufacturing and formulating plants. Hence the waste from these sources must be removed or destroyed before discharge to the environment. There have been several methods practiced for the treatment of wastewater. However many of them are not able to achieve hundred percent satisfaction. Environmental pollution and destruction on a global scale as well as lack of sufficient clean and natural energy sources have drawn much attention and concern to the vital need for ecologically clean chemical technology, materials and processes. This is one of the most urgent challenges facing chemical scientists. Recently, light-induced photocatalytic reactions have gained a lot of attention for the purification of wastewater.

Abstract: Recent interest in nanostructured titanium dioxide (TiO2) has been driven by the excellent photocatalytic and optical properties exhibited by the anatase and rutile phases. This article highlights the relationship between reaction conditions and the resultant nanostructured TiO2 and is primarily focused on wet chemical synthetic methods. We show that solvothermal syntheses of nano-TiO2 can be rationalised by making use of a diffusion-controlled model accounting for physical properties of the solvent such as the vapour-pressure, allowing the prediction and control the phase, size and type of nanostructured TiO2 product. This external control makes it possible for the systematic synthesis of TiO2 nanostructures via parameters such as the solvent chain length, the reaction temperature and time, and also by the addition of surfactants, providing the ability to design and tailor the nanostructured TiO2, which is vital for the optimal application of these nanostructures in photocatalytic or optical applications.

Abstract: Titanium dioxide (TiO2) nanotubes have been reported one decade ago and have proven to be of a great interest in photocatalytic water splitting, as well as gas sensing and anti-bacterial/cancer treatment. This paper presents an overview on general preparation approaches (chemical treatment, template method and anodic oxidation) of tubular TiO2 nanoarchitectures and their characterization. Current applications of the nanotubes as photocatalysts are also reviewed.

Abstract: The present work considers the performance-related properties of TiO2-based photosensitive semiconductors as photocatalysts for water purification and photoelectrodes for water splitting. These properties, including electronic structure, charge transport, surface properties, and near-tosurface properties, have an effect on light absorption and its conversion into chemical energy, and are closely related to defect disorder. Therefore, defect chemistry may be used as a framework for their modification in order to achieve enhanced performance. The present work considers the relationships between these specific performance-related properties and defect disorder.