Nano- versus Micro-sized TiO2: Comparative Photoelectrochemical and Photocatalytic Studies towards Organic Pollutants Oxidation in Gas Phase (original) (raw)
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The photocatalytic activity of micro-and nano-titanium dioxide (TiO 2 ) has been utilized to significantly improve the degradation efficiencies of various contaminants in both water treatment and air pollution control. This article is a review of the literature covering current research on environmental applications of microand nano-TiO 2 . The mechanisms of contaminant degradation of nanoparticle TiO 2 are reviewed, and its special properties are compared to micro-sized TiO 2 in air purification and water treatment.
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A simple, rapid, and effective photoelectrochemical method is proposed to quantitatively characterise photocatalytic degradation behaviour of organic compounds at nanoporous TiO 2 film electrodes in a thin-layer photoelectrochemical cell. This method uses the charge obtained by integrating the photocurrent originating from the photocatalytic oxidation of organic compounds to quantify the extent of degradation. Complete mineralisation was observed for all organic compounds investigated. A double-exponential kinetic rate expression was acquired using a computer simulation method, indicating two simultaneous kinetic processes. Photocurrent profiles of different organic compounds complied well with the proposed theoretical model. Both pre-exponential and exponential constants were obtained. The rate of the fast kinetic component is 10-25 times faster than that of the slow kinetic component. It was found that the identities of organic compounds have no significant effect on the photocatalytic oxidation kinetics, whereas the availability of the organic compounds to capture photoholes plays a decisive role.
Photocatalytic Properties of Commercially Available TiO2 Powders for Pollution Control
Semiconductor Photocatalysis - Materials, Mechanisms and Applications, 2016
The photocatalytic properties of titanium dioxide have been widely studied over recent decades since the discovery of water photolysis by TiO 2 electrodes in 1972. Titanium dioxide has three main crystal polymorphs; anatase, rutile and brookite and rutile is the most common as the metastable polymorph. Each polymorph has different band gap positions. Anatase's band gap is 3.2 eV, higher than rutile's which is 3.0 eV. This difference in the band gap will determine their optimum UV wavelength range to promote a photocatalytic process. There are different methods to assess the photocatalytic activity of a material. The most commonly used method is the degradation of a dye in aqueous solution under UV light, due to its simplicity. Under these conditions the decomposition rate of a suitable organic dye is used as a measure of activity. Physical properties such as particle size and surface area will determine the effective area that will interact and absorb the dye prior to degradation. The physical mechanisms involved in such aqueous based methods differ from gas phase reactions. More advanced techniques use mass spectrometers to evaluate photocatalytic activity of titanium dioxide in the gas phase. An effective photocatalyst for heterogeneous reactions in the gas phase is one which is efficient at creating radicals as a result of an absorbed photon.
Revista Facultad …, 2011
In this work, TiO 2 photocatalysts were synthesized using a conventional sol-gel and hydrothermal synthesis methods with steam pressure treatment. Photocatalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectra (DRS) and N 2 adsorption-desorption. The photoactivity of the samples was analyzed towards the photooxidation of the azo dye Orange II (Or-II) and phenol using different illumination setups to compare the activity features of photocatalysts. The effect of the synthesis variables such as the synthesis route, water/alcoxide and alcohol/alcoxide ratios, as well as the alcohol type was analyzed. TiO 2 photocatalysts obtained by hydrothermal synthesis have a better photoactivity than the particles synthesized by the chosen sol-gel route, reaching the Or-II degradation photoactivity of the commercial TiO 2 P25. On the other hand, the water/alcoxide ratio and alcohol type have a marked effect on the photoactivity of the hydrothermal synthesized TiO 2 , whereas the alcohol/alcoxide ratio does not have a relevant effect on the Or-II degradation photoactivity.
Role of Synthesis Method and Particle Size of Nanostructured TiO 2 on Its Photoactivity
Journal of Catalysis, 2002
TiO 2 prepared by different methods was used to obtain anatase powders with particle sizes ranging from 5 to 165 nm. Powders were prepared using two methods: (i) a flame aerosol process in which nanoparticles of TiO 2 were synthesized in a flame on oxidation (combustion) of an organotitanium precursor, and (ii) calcination of commercially available nanostructured TiO 2 (Ishihara ST-01, 5 nm, as received). For comparison, Degussa P25 and Aldrich anatase TiO 2 powders were also used as received. The TiO 2 powders were characterized using XRD to determine crystal phase and crystal size, BET surface area analyses, uv-vis absorbtion spectroscopy to determine the band gap, and experiments in which the photoxidation rate of phenol in water was used as a measure of photoactivity. A model was developed based on the mechanistic steps in photocatalysis to elucidate the role of particle size on the apparent photoactivity of TiO 2 for the photooxidation of organic substrates in water. The model was used to explain the trends in the experimental data for four different sets of photoactivity experiments with TiO 2 powders. The results of this study elucidate a strong effect of particle size on photoactivity. The effects of particle size on the efficiency of light absorption and scattering and charge-carrier dynamics at particle sizes less than 25 nm dominate the apparent photoactivity of TiO 2 , and an optimum particle size of 25 to 40 nm exists within all sets of photocatalysis experiments conducted with TiO 2 powders in this study. The optimum particle size is a result of competing effects of effective particle size on light absorption and scattering efficiency, charge-carrier dynamics, and surface area.