Colloidal titanium dioxide preparation

Serpone et al. have examined colloidal titanium dioxide sols (prepared by hydrolysis of TiCl4) with mean particle diameters of 2.1, 13.3, and 26.7 nm by picosecond transient absorption and emission spectroscopy [5]. Absorption decay for the 2.1 nm sols was found to be a simple first-order process, and electron/hole recombination was 100% complete by 10 ns. For the 13.3 and 26.7 nm sols absorption decay follows distinct second-order biphasic kinetics the decay times of the fast components decrease with increase in particle size. 10 ns after the excitation pulse, about 90% or more of the photogenerated electron/hole pairs have recombined such that the quantum yield of photooxidations must be 10% or less. The faster components are due to the recombination of shallow-trapped charge carriers, whereas the slower components (x > 20 ns) reflect recombination of deep-trapped electrons and holes. 

Eremenko, B.V. et al., Stability of aqueous dispersions of the hydrated titanium dioxide prepared by titanium tetrachloride hydrolysis, Colloid J., 63, 173, 2001. 

Abstract A colloidal solution of titanium dioxide (TiO ) nanoparticles was prepared by the solvothermal method and dip-coated onto a polypropylene fabric with TMOS binder. The prepared TiO particles, colloidal solution and the coated fabrics were characterized by X-ray diffraction, SEM and TEM. The results showed that the TiO particles prepared by the solvothermal method were composed of anatase which uniformly coated the snbstrate. Photocatalysis induced bactericidal properties of coated fabrics were tested by measuring the viability of Escherichia coli. It was fonnd that solvothermally prepared TiO coatings have the ability to kill E. coli. This nniqne property of TiO makes it an ideal candidate in producing self-sterilizing protective masks and in providing bactericidal and self-cleaning properties to a variety of snrfaces. 

Santacesaria E., Tonello M., Storti G. et al. Kinetics of titanium dioxide precipitation by thermal hydrolisis. J. Colloid Interface Sd. 1986 111 44-56. Reinten Kh.T. Equipment, preparation and properties of hydrated zirconium dioxide. In Structure and Properties of Adsorbents and Catalysts. Ed. Linsen B.G. Moskva Nauka, 1973, p. 332-83. 

These films can be prepared by a variety of routes, only a few of which are mentioned here. The original references should be consulted for more practical details. Titanium dioxide is used as an illustrative example below. First, colloidal solutions are prepared, e.g., from titanium isopropoxide. The resultant sol is concentrated under vacuum at room temperature until its viscosity increases. Then it is spin-coated on to suitable supports (e.g., conducting glass) and fired in an oven. The firing temperature critically controls the morphology of the resultant film as discussed elsewhere [300-303]. Films up to several micrometers thick can be prepared by this simple version of the sol-gel technology [304]. Aerosol or spray pyrolysis is a somewhat related approach [305, 306]. 

Photochemistry of Titanium Dioxide Colloids. Another semiconductor colloid used in our studies is titanium dioxide which has a band gap of 3.2 eV. As in the case of cadmium sulfide, excitation of aqueous suspensions of this particle leads to electron-hole pair separation which can be intercepted with suitable redox reagents. In the absence of externally added solutes, the photogenerated electron-hole pair recombines to give the starting material and the light energy is dissipated to the medium as heat. Two types of TiOj samples are used in this study. TiOj prepared at high temperature (80°C) which behaves very similarly to commercial samples, and TlOj prepared at low temperature (35°C) which has a particle size of 300 100 A radius and shows different properties. 

Magnetic photocatalysts were synthesized by coating titanium dioxide particles onto colloidal magnetite and nanomagnetite particles [197], The photoactivity of the prepared coated particles was lower than that of single-phase Ti02 and was found to decrease with an increase in the heat treatment. These observations were explained in terms of an unfavorable heterojunction between the titanium dioxide and the iron oxide core, leading to an increase in electron-hole recombination. 

Matijevic E., Budnik M., Meites L. Preparation and mechanism of formation of titanium dioxide hydrosols of narrow size distribution. J. Colloid Interface Sci. 1977 61 302-311 MiUs A., Holland C., Davies R., Worsley D. Photomineralization of salicylic acid A kinetic study. J. 

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