Nanotechnology is one of the modern forms of technology that uses very small-sized materials called nano-materials. The prefix ‘nano’ is used to denote a billionth. It is derived from the term “nanometer”, an equivalent of 10-9 m or a billionth of a meter. The dimensions of the nano-materials range from just below a nanometer to a few hundred nanometers, a length equivalent to a linear arrangement of ten hydrogen atoms or five silicon atoms (Cao and Ying 1).
The nano scale measures the transition from molecules or atoms to bulk states. During such transition, materials exhibit some exclusive properties that are of interest to science and technology. Unlike micro-materials which may exhibit these properties in bulk in terms of physical properties, nano-materials exhibit some properties that are not exhibited by bulk materials. For instance, because the ratio of the number molecules, atoms or ions on the surface of a crystal to the total number of the same is very high in comparison to scales beyond the nanometer, the crystals have reduced lattice constants and low melting points. For that reason such physical properties as ferromagnetism and ferroelectricity can be gotten rid of when the materials are miniaturized to the nano scale; semiconductors become insulators in the nano scale; and nano-crystals of gold become effective catalysts at low temperatures.
The scientific application of nano-material to the solution of scientific problems, as well as their use in innovations and inventions is called nano-technology. Nano-technology is generally understood as the design, fabrication and applications of nano-materials and nanostructures (Cao and Ying 3). It is the improved chemical, biological and physical phenomena, properties and processes of these nano-scale materials that are exploited in the field of nano-science.
Synthesis of Nano-materials
The synthesis of nano-materials is the production of materials that posses the special exploitable properties that are not exhibited by materials that are out of the nano-scale. The synthesis of nano-materials is achieved by two main avenues: bottom up and top down.
Bottom-up approach refers to the synthesis of a nano-material by building it from the bottom upwards: atom after atom, molecule after molecule or cluster after cluster. The bottom-up approach is not new as it has been around for a while. Some of the common applications of the bottom-up approach are polymer science where the synthesis of polymers is achieved by linking monomers together; and the process of crystallization where the crystal grows by the attachment of ions, molecules or atoms onto the growth surface. The bottom up approach is instrumental in the synthesis of nano-materials because the tools available are too big for the convenient and successful implementation of the top-up approach, its alternative.
The beauty of the bottom up approach lies in the fact that it provides a high chance of obtaining nano structures with minimum defects, high homogeneity in chemical composition, and better ordering, in both long and short range. This is because the bottom-up approach relies on the lowering of Gibbs free energy so that the so produced nano-materials are almost in a thermodynamic equilibrium state (Cao and Ying 10).
Two of the typical methods of implementing top-down approach are milling and attrition. One of the biggest limitations of the top-down approach is that the nano materials produced by it have imperfect surface structures. Lithography and other conventional top-down techniques cryptographically damage the processed patterns, and that etching steps may introduce more defects, as well as impurities (Cao and Ying 9). Such imperfections can source significant limitations in the nano-materials as regards their surface chemistry and physical properties, owing to the high surface area to volume ratio of nano-materials. For instance, a distorted surface would lower conductivity because of its inelastic surface scattering, the result of which would be an overheating, posing a challenge to the design and fabrication process. The technique continues to play a significant role in spite of its limitations.
Applications of Nano-materials
The peculiar properties of nano-particles have been exploited for science and technological development. Nano-materials have had several applications in science because of their exclusive properties. Some of the nano-materials that have found applications or have the potential for applications include carbon nanotubes, graphene, nanofibers, nanoparticles and nanowires.
A carbon nanotube is one of the nano-materials whose applications are being developed. One of the prospective applications of carbon nanotubes is their use as sensors for bacteria, which is achieved by the addition of antibodies to them. The nanotubes can also be used to trap oil spills when gold or boron is added to them as well as design smaller transistors, among other applications.
Nano-scale Graphene is being developed for use in ultracapactors which make use of graphene electrodes and are predicted to be capable charge storage capacity high enough to rival batteries and be rechargeable in minutes. When attached to strands of DNA, the graphene can act as sensors for medical complications, facilitating rapid diagnosis.
A nanofiber is also a type of nano-materials that has found applications in many areas of life. Nanofibers are simply fibers in the nano scale. Damaged joints can be repaired by the production of cartilage, a process that nanofibers have been found to stimulate. Nanofibers are also used to produce, by the application of pressure, tiny amounts of electricity in piezoelectric nanofibers, which can be fixed on clothes to produce electricity for such devices as watches and mobile phones.
Nanoparticles have been applied in biology and other areas of life. They have found applications in the direct delivery of chemotherapy drugs to damaged regions of arteries and cancerous cells. The nanoparticles have also been used to mimic photosynthensis in their application as photocatalysists in the decomposition of water to produce hydrogen. They are also used to clear polluted air and water.
Nano-materials in the form of nanowires have electrical applications also. Nanowires made of zinc oxide have been used in the manufacture of solar cells that are flexible. Organic molecules in polluted water are decomposed by nanowires made of silver chloride. When made of nickel and iron, nanowires are used to make dense computer memories.
Environmental and Health Hazards
Nano-materials have a side opposite the numerous benefits they have; and that is their negative impacts to both the ecological system and the health of living things. Exposure to nano-material poses significant health risks. Exposure can occur through using products made using nanotechnology or coming into contact with an environment that is “polluted” with nano-particles. For instance, nano-materials have a very high surface area to volume ration because of the miniature proportions. Various metabolic processes are dependent on the property of surface area to volume ratio. The small size of nano-particles make it easy for them to penetrate biological systems. Upon entry, they can significantly modify bio-molecules thereby disrupting biological functions. This property is also exploited in certain forms of medical therapy. Hence, it is important that the use of nano-materials be carefully monitored.
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