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Nanocrystalline titanium dioxide

Nanocrystalline titanium dioxide (TiO2) finds wide application in the fabrication of solar cells, fuel cells, electrical and photocatalytic systems because of it is highly stable, non-toxic and has a suitable redox potential for photodegrading pollutants. Studies are being conducted on the development of the immobilization technique that can maintain high surface area and excellent physicochemical properties of TiO2 for photocatalysis with a focus on the use of TiO2 nanoparticles for the purposes of improving the catalytic efficiency with respect to the high surface-to-volume ratio.
Fabrication methods
Nanocrystalline TiO2 films made using sol-gel technique can be used in direct methanol fuel cell (DMFC). Titania thin films is made using sol-gel technique, direct deposition from aqueous solution, sputtering technology, ultrasonic spray pyrolysis and hydrothermal crystallization. The sol-gel technique of preparing TiO2 thin film on the substrates has many advantages over other methods such as chemical vapour deposition (CVD), plasma spraying, anodization and thermal oxidation of Ti metal mainly because it requires no special apparatus, uniform muticomponent films can easily be formed if a homogeneous solution is available, phase structure of film can be controlled, in this case TiO2 (anatase) can be obtained and the resultant films may be characterized by structure of a gel with a large specific area characteristic.TiO2 thin films of high specific area can also be obtained from a TiO2 sol prepared by hydrothermal treatment of peroxotitanic acid sol or alkoxide derived TiO2 gel.Low-temperature synthesis of nanocrystalline TiO2 anatase is difficult when using sputtering technology and CVD method as the temperatures used in these synthesis methods usually are high at about 300°C or morefor getting crystalline anatase.
Vietnam Can Tho University researchers have used Sol-gel technique with glass and Nafion substrates to get nanocrystallline at low temperature of 60°C. Titanium tetraisopropoxide (TTIP) (98%), ethanol (99.5%), HCl (37%), water and PEG 600 are used as the starting materials. Water and 3% of PEG 600 (average molecular weight of 600) are then introduced to the mixture accompanied by vigorous stirring at 80°C to allow the formation of a stable, homogenous and transparent sol solution. Following the process, titania sol formed by the procedure is deposited on the substrates of glass and Nafion membrane by spin coating. The substrates coated by titania sol are taken out and dried at 60°C in a vacuum dryer machine for 8 hours.
Water purification
Nano TiO2 is used in water purification systems. There are several technologies which might compete with nano TiO2 for applications in water purification based on activated charcoal and high-intensity UV light. Another nanotechnology widespered is the sol-gel process which is used to produce long nanofibres of alumina containing nano-titania particles. In this process the interstices in the fibres can be made to be of the same order as the dimensions of viruses and bacteria which can then be filtered from air or water.
TiO2 which is an n-type semiconductor has photocatalytic germicidal properties in the nano-particulate form. Disinfection or purification systems can be created based on nanoparticulate TiO2. For this it has to be directly attached to a surface or to use the sol-gel process, for example, to apply a thin layer of particles on a substrates such as metal, alloys, glass, glass fibre, cellulose, plastics, ceramics and wood. The process is first to lay down on a surface an adhesive layer formed from a silica sol which is not affected by the photocatalysis. Then a layer of photocatalytic particles is deposited upto 100 nm thick using a sol containing nanoparticulate TiO2 and a silica additive which increases adhesion.

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