Nano Info

Nano technology is not a mysterious science, it exists with us as long as we have been here on earth; cavemen used the nano pigment to paint pictures, some of the red colour in the church windows made before nineteen century is actually mixed with gold nano particles ....etc.

Nano Meter

     


What are "Nano Meter" and "Nano Technology" ?

One nano meter is a unit of a length: 1nm = 1X10-9 m,  or equivalent to 0.000 000 001m.

Perhaps it would be easier to visualize the ratio between  1 m and 1nm, it  is roughly the size of the earth to three table-tennis balls. Nano technology is about new applications of the materials that have the length or diameters from  the range of  1nm to less than 100nm.

Materials in this region will present some unusual physical properties than those of their counter parts.   For example, increase in melting points, red shift  or blue  shift in electromagnetic wave absorption… etc. With these newly discovered properties, scientists and engineers open up a whole new chapter on the applications, perhaps a new industrial revolution has already started. Nano technology covers all area of our daily life including material science, environmental protection, life science, catalyst ...etc.

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The Photocatalyst

In 1967, a Japanese scientist, Dr. Akira Fujishima, discovered a very important photocatalytic phenomena; it is just like the reverse process of photosynthesis of plants that converts CO2 and H2O to organics. He observed that certain semi-conductors such as titanium dioxide (TiO2) and znic oxide (ZnO) when received UV radiation (Ea), they will generate a pair of electron and electron-hole. They are very unstable and react with water and oxygen to form oxygen and hydroxyl radicals (O2-, OH·). These radicals are very aggressive intermediates; they react with the surrounded organics and convert them to carbon dioxide and water.

 

Diagram of an Exothermic Reaction with an External Activation Energy, Ea

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The Reaction Mechanism

The Reaction Mechanism of Formaldehyde by Photocatalyst
(source: http://www.photocatalyst.co.jp)

 

The oxidizing power of the intermediates is very powerful, it is able to oxidize organics such as PCBs (polychlorinated biphenyl) and other POPs (Persistent Organic Pollutants) e.g. dioxins, in ambient temperature.  For those who wants to know more about PCBs, please visit: http://en.wikipedia.org/wiki/Polychlorinated_biphenyl

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Testing of Photocatalyst Efficiency

 

       

 
Diagram Source: http://en.wikipedia.org/wiki/Methylene_blue

 

A common method to measure the efficiency of any photocatalystic products in water treatment is by determining the TOC (Total Oxidizable Carbon) values of the samples before and after the product exposed to the light source over a period of time.

 

However, the analytical method of measuring the TOC of water sample is very costly and complicated. SITPA (Society of Industrial Technology for Photocatalytic Articles) of Japan has proposed a method (only Japanese version is available) to test any products that have photocatalytic effects.

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