What comes to your mind when you hear the term ‘nanoparticles’?
Logical answer would be ‘particles with size of 10^-9 m’.
And it’s quite right.
A nanoparticle (or nanopowder or nanocluster or nanocrystal) is a microscopic particle with at least one dimension less than 100 nm.
Hence, in general the size of a nanoparticle ranges between 1 and 100 nm. Metallic nanoparticles have a different physical and chemical properties from bulk materials (higher surface areas, specific optical properties, lower melting points, etc.), properties that might prove attractive in various applications.
For example, the bending of bulk copper (wire, ribbon, etc.) occurs with movement of copper atoms/clusters at about the 50 nm scale. Copper nanoparticles smaller than 50 nm are considered super hard materials that do not exhibit the same malleability and ductility as bulk copper.
Nanoparticles often have unexpected visible properties. For example, gold nanoparticles appear dark red to black in solution.
Nanoparticles have high surface to volume ratio. This provides a tremendous driving force for diffusion, especially at elevated temperatures.
Air pollution can be remediated using nanotechnology in several ways. One is through the use of nano-catalysts with increased surface area for gaseous reactions. Catalysts work by speeding up chemical reactions that transform harmful vapors from cars and industrial plants into harmless gases. Catalysts currently in use include a nanofiber catalyst made of manganese oxide that removes volatile organic compounds from industrial smokestacks.
Another approach uses nanostructured membranes that have pores small enough to separate methane or carbon dioxide from exhaust.
The substances filtered out still presented a problem for disposal, as removing waste from the air only to return it to the ground leaves no net benefits.
As with air pollution, harmful pollutants in water can be converted into harmless chemicals through chemical reactions. Trichloroethene, a dangerous pollutant commonly found in industrial waste water, can be catalyzed and treated by nanoparticles.
Also widely used in separation, purification, and decontamination processes are ion exchange resins, which are organic polymer substrate with nano-sized pores on the surface where ions are trapped and exchanged for other ions. Ion exchange resins are mostly used for water softening and water purification. In water, poisonous elements like heavy metals are replaced by sodium or potassium. However, ion exchange resins are easily damaged or contaminated by iron, organic matter, bacteria, and chlorine.
Recent developments of nano-wires made of potassium manganese oxide can clean up oil and other organic pollutants while making oil recovery possible. These nanowires form a mesh that absorbs up to twenty times its weight in hydrophobic liquids while rejecting water with its water repelling coating. Since the potassium manganese oxide is very stable even at high temperatures, the oil can be boiled off the nanowires and both the oil and the nanowires can then be reused.