Titanium dioxide chemistry

The analytical chemistry of titanium has been reviewed (179—181). Titanium ores can be dissolved by fusion with potassium pyrosulfate, followed by dissolution of the cooled melt in dilute sulfuric acid. For some ores, even if all of the titanium is dissolved, a small amount of residue may still remain. If a hiU analysis is required, the residue may be treated by moistening with sulfuric and hydrofluoric acids and evaporating, to remove siUca, and then fused in a sodium carbonate—borate mixture. Alternatively, fusion in sodium carbonate—borate mixture can be used for ores and a boiling mixture of concentrated sulfuric acid and ammonium sulfate for titanium dioxide pigments. For trace-element deterrninations, the preferred method is dissolution in a mixture of hydrofluoric and hydrochloric acids. 

In the 1970s, textbook publishers (and other entrepreneurs) found that adding titanium dioxide to paper as a filler and whitener enormously increased its opacity (Figure B). This allowed for the use of thinner paper without having the type "bleed" from one side to the other. Perhaps this explains, at least in part, why most chemistry textbooks today (but not this one) run to a thousand pages or more. 

Two processes are used in the manufacture of titanium dioxide pigments the sulfate process and the chloride process. The chemistry of the sulfate process, the longer established of the two methods, is illustrated schematically in Scheme 9.1. In this process, crude ilmenite ore, which contains titanium dioxide together with substantial quantities of oxides of iron, is digested with concentrated sulfuric acid, giving a solution containing the sulfates of Ti(iv), Fe(m) and Fe(n). Treatment of this... 

Carp, O., Huisman, C.L., and Reller, A. (2004) Photoinduced reactivity of titanium dioxide. Progress in Solid State Chemistry, 32 (1-2), 33-177. 

Kowalska, E., Remita, H., Colbeau-Justm, C., Hupka, J., and BelloniJ. (2008) Modification of titanium dioxide with platinum ions and dusters application in photocatalysis. Journal of Physical Chemistry C, 112 (4), 1124-1131. 

Hirano, K., Inoue, K., and Yatsu, T. (1992) Photocatalysed reduction of C02 in aqueous Ti02 suspension mixed with copper powder. Journal of Photochemistry and Photobiology A Chemistry, 64 (2), 255-258. Adachi, K., Ohta, K., and Mizuno, T. (1994) Photocatalytic reduction of carbon dioxide to hydrocarbon using copper-loaded titanium dioxide. Solar Energy,... 

Brezova, V., Blazkova, A., Surina, I., and Havlmova, B. (1997) Solvent effect on the photocatalytic reduction of 4-nitrophenol in titanium dioxide suspensions. Journal of Photochemistry and Photobiology A Chemistry, 107 (1-3), 233-237. 

At present, titanium dioxide meets green chemistry principles, including energy efficiency and renewable feedstocks through a wide variety of heterogeneous photo-... 

This chapter has been concerned mainly with the chemistry of making pigments but has also stressed the importance of preparing them in the correct physical form. In the case of those pigments which can be made in more than one crystal form, such as the anatase and rutile forms of titanium dioxide, this may mean that all the pigment should be in one form only. In others, a mixture of polymorphic forms may be required, and it is then necessary to ensure that the desired ratio of these forms is present. 

Titanium dioxide differs from silica mainly in two respects (1) the Ti + ions are octahedrally coordinated in all three modifications of TiOji (2) the Ti—0 bond is more pronouncedly ionic than the Si—O bond. Using Pauling s electronegativity values (297), one calculates a 63% ionic character for the Ti—0 single bond versus 50% for Si—O. In SiOj, there is certainly some double bond character involving 3d orbitals of the Si atom, causing lowered ionic character. Therefore, characteristic differences should be expected regarding the surface chemistry. 

Titanium dioxide occurs in three crystalline modifications anatase, rutile, and brookite. In all three forms, each Ti + ion is surrounded by six 0 ions and each ion has three Ti + neighbors. Both anatase and rutile are important white pigments which are produced on a large scale. Even though their surface chemistry is very important for their technological application, astonishingly little has been published in the chemical literature on this subject. However, it is very likely that many investigations have been undertaken in industrial laboratories. 

Blake DM, Maness PC, Huang Z, Wolfrum EJ, Huang J, Jacoby WA. Application of the photocatalytic chemistry of titanium dioxide to disinfection and the killing of cancer cells. Sep Purif Methods 1999 28 1-57. 

Bahnemann, D.W., J. Monig and R. Chapman (1987b). Efficient photocatalysis of the irreversible one-electron and two-electron reduction of halothane on platinized colloidal titanium dioxide in aqueous suspension. Journal of Physical Chemistry, 91(14), 3872-3788. 

Bilmes, S.A., P. Mandelbaum, F. Alvarez and N.M. Victoria (2000). Surface and electronic structure of titanium dioxide photocatalysts. Journal of Physical Chemistry B, 104, 9851-9858. 

Karvinen, S.M. (2003). The effects of trace element doping on the optical properties and photocatalytic activity of nano structured titanium dioxide. Industrial and Engineering Chemistry... 

Kormann, C., D.W. Bahnemann and M.R. Hoffmann (1988). Preparation and characterization of quantum-size titanium dioxide. Journal of Physical Chemistry, 92(18), 5196-5201. 

Kuznetsov, V.N. and N. Serpone (2006). Visible light absorption by various titanium dioxide specimens. Journal of Physical Chemistry B, 110, 25203-25209. 

Lindgren, T., J.M. Mwabora, E. Avendano, J. Jonsson, A. Hoel, C.G. Granqvist and S.E. Lindquist (2003). Photoelectrochemical and optical properties of nitrogen doped titanium dioxide films prepared by reactive DC magnetron sputtering. Journal of Physical Chemistry B, 107(24), 5709-5716. 

Serpone, N. (2006). Is the band gap of pristine Ti02 narrowed by anion- and cation-doping of titanium dioxide in second-generation photocatalysts Journal of Physical Chemistry B, 110(48), 24287-24293. 

Paz, Y. Composite Titanium Dioxide Photocatalysts and the Adsorb Shuttle Approach A review , in Solid- State Chemistry and Photocatalysis of Titanium Dioxide . Nowotny J. (Editor), Trans Tech Publications, UK [in press]. 

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