The principles of titanium oxide photocatalysts and photocatalytic reactions have been briefly introduced as compared to the photosynthesis in green plants. Photocatalysis can be considered the most important and new, environmentally friendly, clean chemical technology for green chemistry. In fact, various applications of titanium oxide photocatalysts have already been developed to better our environment. Especially, these include successful developments in the purification of the polluted atmosphere. The design and development of such unique titanium oxide photocatalysts can be considered a breakthrough in the efficient and large-scale utilization of solar energy.  

The photocatalytic reactivity of titanium oxides can be applied for the reduction or elimination of polluted compounds in air such as NOx, cigarette smoke, as well as volatile compounds arising from various construction materials. Also, high photocatalytic reactivity can be applied to protect lamp-houses and walls in tunneling, as well as to prevent white tents from becoming sooty and dark. Atmospheric constituents such as chlorofluorocarbons (CFCs) and CFC substitutes, greenhouse gases, and nitrogenous and sulfurous compounds undergo photochemical reactions either directly or indirectly in the presence of sunlight. In a polluted area, these pollutants can eventually be removed. 

Titanium oxide thin films have been found to exhibit a unique and useful function (i.e., a super-hydrophilic property). Usually, metal oxide surfaces such as titanium oxides become cloudy when water is dropped on them because the contact angle of the water droplet and the surface is 50–80 degrees.

The use of UV light bulbs to photocatalytically destroy pollutants provides extremely simple controls. The unit can be turned on or off with the flip of a light switch. The ambient operating temperature result in low energy consumption, and provides low cost.

The process can be integrated with other flue gas cleanup technologies to achieve ultra-low Nox and SO2 emissions. In addition, it offers the following distinctive advantages:

• Potential utilization of solar energy with semiconductor particles (TiO2)
• No extra reactants such as NH3 or O3 required
• Low temperature operations
• Nox recovered as nitric acid, a potential raw material for fertilizers

Some practical applications are as follows:

• Air cleaner containing TiO2 photocatalysts.

• Systems for the purification of polluted air, e.g., the elimination of NOx

• Super-hydrophilic, self-cleaning systems, and coating materials for cars.

• Soundproof walls using TiO2 photocatalysts

• Photocatalyst coated lamps (or lamp covers

• Cement containing TiO2 photocatalysts

• Coating materials for architectural walls.

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