Applications of Titanium Dioxdie Nanocoating Behzad Rezaei 1, Hamid Mosaddeghi 2 1, 2 Department of Chemistry, 1 rezaei@cc.iut.ac.ir 2 h.mosaddeghi@ch.iut.ac.ir Abstract Metal oxide semiconductors, such as TiO 2 nanoparticles are frequently used as photocatalyst due to nontoxicity, chemical stability, and the ability to possess relatively high photocatalytic activity of TiO 2. Laboratory studies have demonstrated that organic compounds such as alcohols, carboxylic acid, phenolic derivatives, and chlorinated aromatics can be readily mineralized by TiO 2 into harmless carbon dioxide, water and simple mineral acids, using molecular oxygen as the primary oxidant. Keywords: Titanium oxide - Environmental pollution - photocatalytic degradation process Introduction Nanotechnology is not just about the size of very small things, it is the revolutionary science and the art of manipulating matter at the atomic or molecular scale. More important, it is about the structure and the ability of molecular compounds to "work". Research in areas related to nanomaterial is needed to develop manufacturing techniques. In particular, it is a synergy of top-down with bottomup processes. When matter is as small as 1 to 100 nanometers, many of its features will easily change and have many unique features both different from macro-matters and single atoms due to the quanta effect, regional confinement of matter, and huge surface or interface effects. The final objective of nanometer technology is to produce products of Special functions with new physical and chemical features by making atoms, molecules and matters presenting their features directly in the length of a nanometer. In recent years, metal oxide nanoparticles have attracted much attention by their potential application in diverse fields including catalysis, magnetic recording media, microelectronics, medicine. For example, titanium oxide nanoparticles (fig.1) are very important due to their various applications; removing the environmental pollution, sterilization and restraining virus, defending UV, keep rust away, and depigment[1]. The element Titanium was discovered in 1791 by William Gregor, in England. Four years later a man named Martin H. Klaproth, recognized that there was a new chemical element in this mineral, he later named it Titanium after the Titans, which were humongous monsters that ruled the world in Greek mythology. Martin H. Klaproth was not able to make the pure element of titanium however; he was only able to produce TiO2, or Titanium Dioxide[2]. Titanium dioxide (TiO2) is a multifaceted compound. It's the stuff that makes toothpaste white and paint opaque. TiO2 is also a potent photocatalyst that can break down almost any organic compound when exposed to sunlight, and a number of companies are seeking to capitalize on titanium dioxide s reactivity by developing a wide range of environmentally beneficial products, including self-cleaning fabrics, auto body finishes, 1 Assoc.Prof. of Analytical chemistry 2 Msc Student of Physical chemistry
and ceramic tiles. Also one development is a paving stone that uses the catalytic properties of TiO 2 to remove nitrogen oxide from the air, breaking it down into more environmentally benign substances that can then be washed away by rainfall. Other experiments with TiO 2 involve removing the ripening hormone ethylene from areas where perishable fruits, vegetables, and cut flowers are stored; stripping organic pollutants such as trichloroethylene and methyl-tert-butyl ether from water; and degrading toxins produced by bluegreen algae. It remains to be seen, however, whether the formation of undesirable intermediate products during these processes outweighs the benefits offered by TiO 2 's photocatalytic properties. Titanium dioxide is a well-known photocatalyst for water and air treatment as well as for catalytic production of gases. The general scheme for the photocatalytic destruction of organics begins with its excitation by suprabandgap photons, and continues through redox reactions where OH radicals, formed on the photocatalyst surface, play a major role. Titanium dioxide is non-toxic and therefore is used in cosmetic products (sunscreens, lipsticks, body powder, soap, pearl essence pigments, tooth pastes) and also in special pharmaceutics. Titanium dioxide is even used in food stuffs, for instance in the wrapping of salami. Titanium dioxide s photocatalytic characteristics are greatly enhanced due to the advent of nanotechnology. At nano-scale, not only the surface area of titanium dioxide particle increases dramatically but also it exhibits other effects on optical properties and size quantization. An increased rate in photocatalytic reaction is observed as the redox potential increases and the size decreases. Applications of titanium oxide photocatalyst Photocatalysis refers to the chemical reaction that occurs when light strikes a chemical compound that is light sensitive, such as titanium oxide. When light strikes titanium dioxide, a chemical reaction repeated in the immediate region and causes the breakdown of organic toxins, odors, and more. This reaction has many valuable results; several of important applications are listed below (fig.2) Environmental improvement applications: TiO 2 causes remove environmental pollution substances, such as NO x emitted by exhaust gas etc. from the atmosphere. SO x, a detrimental inorganic matter in the atmosphere is also broken down. TiO 2 doesn't cover up smells, like conventional air fresheners, it actually attacks the root of the smell by causing the breakdown of the origin of the odor (ammonia, aldehyde gas [smoke], etc). (fig.3) Water purifying applications: TiO2 also causes detrimental organic matter such as organic chlorine compounds, tetrachlorethylene, trihalomethane and other harmful substances to broken down[3]. (fig.4). For example, chloroform breaks down according to the process below: H 2 O + CHCl 3 + (1/2)O 2 CO 2 + 3HCl Pharmaceutical applications Sterilization, restraining virus; TiO2 photocatalyst can destroy the membrane of cells; solid the proteins of viruses, restrain the virus activation, and catching them. It kills bacterias up to 99.97%. TiO 2 can kill coliform, green suppuration bacillus, golden grape coccus, mildew, suppuration fungus, etc.the ability of sterilization can be tested through coliform and golden grape coccus. At the beginning, there are 3.3 10 5 coliforms and 3.2 10 5 golden grape coccus. After 24 hours reaction, there are only 10[4]. Mechanism of titanium dioxide photocatalytic degradation process Under illumination, the TiO2 photocatalyst absorbs photons with energy equal or higher than its band gap energy (λ <385nm). This will delocalizes a valence electron and excites it to the conduction band of this semiconductor. These photo excited charge carriers can initiate the degradation of the adsorbed chemical species by one or more forms of electron transfer reactions. However, alternatively, they can recombine radiatively or non-radiatively and dissipating the input energy as heat[5]. (fig.5) To improve the efficiency, Fe and Er are used as additives with TiO 2. Then it can be used in visible region as the band gap energy reduces[6]. Figures and Graphs References 1. United States Patent 6653356 2. Greenwood N.N., Earnshaw A. Chemistry of the elements, pp 954, Elsevier, 1997. 3. Ollis, D.F.,Alekabi,Matthews,R.W. In Photocatalytic Purification and Treatment of Water and Air, Eds. Elsevier, Amsterdam,1993. Deodorization applications:
4. Ireland, J.C. et. al. Inactivation of Escheria coli by Titanium Dioxide Photocatalytic Oxidation. Applied and Environmental Microbiology. May 1993. 5. Http://www.aircleanmedium.com 6. Http://www.freepatentsonline.com
Fig 1. TEM image of titanium dioxide Nanoparticles Fig 2. Applications of Titanium Dioxide
Fig 3. The Function of Decomposing Aldehyde Fig 4: Decomposing of oil contamination (A: first day, B: third day, C:fifth day, D:7th day )
Fig 5. Mechanism of titanium dioxide photocatalytic degradation process