Titanium dioxide, adsorption

Nanoparticles of the semicondnctor titanium dioxide have also been spread as mono-layers [164]. Nanoparticles of TiOi were formed by the arrested hydrolysis of titanium iso-propoxide. A very small amount of water was mixed with a chloroform/isopropanol solution of titanium isopropoxide with the surfactant hexadecyltrimethylammonium bromide (CTAB) and a catalyst. The particles produced were 1.8-2.2 nm in diameter. The stabilized particles were spread as monolayers. Successive cycles of II-A isotherms exhibited smaller areas for the initial pressnre rise, attributed to dissolution of excess surfactant into the subphase. And BAM observation showed the solid state of the films at 50 mN m was featureless and bright collapse then appeared as a series of stripes across the image. The area per particle determined from the isotherms decreased when sols were subjected to a heat treatment prior to spreading. This effect was believed to arise from a modification to the particle surface that made surfactant adsorption less favorable. 

We have developed a compact photocatalytic reactor [1], which enables efficient decomposition of organic carbons in a gas or a liquid phase, incorporating a flexible and light-dispersive wire-net coated with titanium dioxide. Ethylene was selected as a model compound which would rot plants in sealed space when emitted. Effects of the titanium dioxide loading, the ethylene concentration, and the humidity were examined in batches. Kinetic analysis elucidated that the surface reaction of adsorbed ethylene could be regarded as a controlling step under the experimental conditions studied, assuming the competitive adsorption of ethylene and water molecules on the same active site. 

Shiraishi, Y., Saito, N., and Hirai, T. (2005) Adsorption-driven photocatalytic activity of mesoporous titanium dioxide. Journal of the American Chemical Society, 127 (37), 12820-12822. 

Heat-flow calorimetry may be used also to detect the surface modifications which occur very frequently when a freshly prepared catalyst contacts the reaction mixture. Reduction of titanium oxide at 450°C by carbon monoxide for 15 hr, for instance, enhances the catalytic activity of the solid for the oxidation of carbon monoxide at 450°C (84) and creates very active sites with respect to oxygen. The differential heats of adsorption of oxygen at 450°C on the surface of reduced titanium dioxide (anatase) have been measured with a high-temperature Calvet calorimeter (67). The results of two separate experiments on different samples are presented on Fig. 34 in order to show the reproducibility of the determination of differential heats and of the sample preparation. 

Gold, chloride, adsorption, magnetite, goethite, alumina, titanium dioxide, hydrometallurgy... 

Kale, S. S. Mane, R. S. Chung, H. Yoon, M.-Y. Lokhande, C. D. Han, S.-H. 2006. Use of successive ionic layer adsorption and reaction (SILAR) method for amorphous titanium dioxide thin films growth. Appl. Surf. Sci. 253 421 424. 

Y. lizuka, T. Tode, T. Takao, K. Yatsu, T. Takeuchi, S. Tsubota, and M. Haruta, A kinetic and adsorption study of CO oxidation over unsupported fine gold powder and over gold supported on titanium dioxide, J. Catal. 187(1), 50-58 (1999). 

Ganichenko and Kiselev (303) and Ganichenko et al. (304) studied the adsorption of water and determined the corresponding heats of adsorption. They concluded that hydroxyl groups exist on titanium dioxide even after outgassing at high temperatures. 

A great deal of adsorption work has been carried out using titanium dioxide as an adsorbent, following extensive work with this material by Harkins and Jura 169). In one series of accurate calorimetric experiments, the initial temperature of evacuation was 300° C. 96). Any grease present on the rutile before degassing would not have been removed by this treatment. Recent work 170) has shown that it is possible that rutile may be subject to hydrocarbon contamination. 

In considering photoactivity on metal oxide and metal chalcogenide semiconductor surfaces, we must be aware that multiple sites for adsorption are accessible. On titanium dioxide, for example, there exist acidic, basic, and surface defect sites for adsorption. Adsorption isotherms will differ at each site, so that selective activation on a particular material may indeed depend on photocatalyst preparation, since this may in turn Influence the relative fraction of each type of adsorption site. The number of basic sites can be determined by titration but the total number of acidic sites is difficult to establish because of competitive water adsorption. A rough ratio of acidic to basic binding sites on several commercially available titania samples has been shown by combined surface ir and chemical titration methods to be about 2.4, with a combined acid/base site concentration of about 0.5 mmol/g . 

The dried block copolymer-coated titanium dioxide particles were dispersed in toluene (secondary dispersions) and subjected to the settling test described in the experimental section. In the first few experiments, dispersions with 9.1% solids were prepared later, under standardized conditions, the solids content of the dispersions was 10 wt %. Adsorption and settling data obtained under these conditions are given in Table I. The settling data of the first three samples of this table are plotted in Figure 2. 

After all other conditions had been optimized, the effect of temperature during the adsorption step was studied again, particularly because the temperature reduction from 150° to 100 °C had no deleterious effect on dispersion stability. Adsorption of the block copolymer onto the titanium dioxide at room temperature would be easy to carry out in practical applications and might be worth even a sacrifice in dispersion stability. Figure 4 shows settling data of dispersions prepared in a Waring... 

Lu, M., Roam, G., Chen, ]., and Huang, C., Adsorption characteristics of dichlorvos onto hydrous titanium dioxide surface, Water Res., 30, 1670, 1996. 

Hydrous titanium dioxides (T1O2 nH20, where >()) may also be important sorbents for arsenic species. Manna, Dasgupta and Ghosh (2004) investigated the removal of As(III) with synthetic crystalline hydrous titanium dioxide. At pH 7, the adsorption capacity of the compound was 72-75 mg g-1. Approximately... 

Balaji, T. and Matsunaga, H. (2002) Adsorption characteristics of As(III) and As(V) with titanium dioxide loaded amberlite XAD-7 resin. Analytical Sciences, 18(12), 1345-49. 

Jezequel, H. and Chu, K. (2006) Removal of arsenate from aqueous solution by adsorption onto titanium dioxide nanoparticles. Journal of Environmental Science and Health, Part A Toxic/Hazardous Substances and Environmental... 

The direct charge transfer to dichloroacetate proposed in reaction (7.21) requires that the scavenging molecules are adsorbed on the Ti02 surface prior to the adsorption of the photon. Otherwise, this reaction could not compete with the normal hole-trapping reactions (7.9) and (7.10). So the adsorption of the model compound DCA on the titanium dioxide surface prior to the bandgap excitation appears to be a prerequisite for an efficient hole scavenging. 

The specific surface area S of the same titanium dioxide powders for which 2R values were measured in [109] (Fig. 8.3) was determined by low-temperature nitrogen adsorption by using the BET method (Fig. 8.5) [110]. The surface area ST (in m2/g) can also be calculated from the experimentally measured 2R values using equation (8.5) ... 

At the adsorption onto titanium dioxide surface, vanadium ions form, at the beginning, randomly distributed isolated V4+ centers with typical D4h symmetry (gy < gx, Ay > A for the unpaired electron). At higher vanadium concentrations, monolayers and... 

It is a mass transfer between a mobile, solid, or liquid phase, and the adsorption bed packed in a reactor. To carry out adsorption, a reactor, where a dynamic adsorption process will occur, is packed with an adsorbent [2], The adsorbents normally used for these applications are active carbons, zeolites and related materials, silica, mesoporous molecular sieves, alumina, titanium dioxide, magnesium oxide, clays, and pillared clays. 

The book explores various examples of these important materials, including perovskites, zeolites, mesoporous molecular sieves, silica, alumina, active carbons, carbon nanotubes, titanium dioxide, magnesium oxide, clays, pillared clays, hydrotalcites, alkali metal titanates, titanium silicates, polymers, and coordination polymers. It shows how the materials are used in adsorption, ion conduction, ion exchange, gas separation, membrane reactors, catalysts, catalysts supports, sensors, pollution abatement, detergency, animal nourishment, agriculture, and sustainable energy applications. 

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