Carbon nanotubes are elongated cylindrical structures with a diameter of one to several tens of nm(nanometres) and length up to several microns comprised of one or more hexagonal planes of graphite (graphene) rolled into a nanotube, usually ended with hemispherical head.
They were first discovered in 1991, can be single-walled or multi-walled. Accordingly, the diameter of these nanotubes is in the range of 0.4 – 500 nm, with a length varying from 1 micron to several tens of micrometres These nanotubes are formed by the decomposition of carbon- based gases on catalytically active surfaces of metals like Iron, Cobalt, Nickel etc.
in temperatures around 300 – 1500° C. They can take a variety of forms, from straight to twisted fibres (including spirals). The main feature of these carbon nanotubes are their frame structure. Identified natural forms of carbon nanotubes can be produced artificially. It is found that the natural nanotubes are formed during the processing of carbon-biological tissue by specific fungi, discovered, particularly in karstic caves of New Zealand and in Karelia.
It has been discovered that many countries have encountered with minute, physical and economical water scarcities, while some are waiting for the same approach. In the last century, water usage has been more than twice the rate of population growth , resulting in global water scarcity. Such fresh water crisis brings problems not only to human, but also to the eco-systems. It has already affected many continents, mainly developing countries, which accommodate almost 40% region of our planet . People in the developing countries depend mainly on the ground water facility due to the lack of expensive water puriﬁcation techniques.
Approximately 30% of the fresh and clean water accumulated in aquifers have commonly been utilized for irrigation to cultivate food grains, vegetables and fruits, leading to a water depletion of about 12 billion m3/year , endangering bio diversities, ﬂora and fauna.
During past years, there have been considerable achievements, and, as an example, carbon nanotube research progress for fourteen years, from 1990 to 2003, is described by Golnabi et al. (2006). Considerable efforts have been made in the development of new synthesis methods of nanotube production and related test equipment for fabrication of high quality nanotubes and nanofibers. From the explored search under the topic “carbon nanotubes”, the total number of publications for the period of 1990–2003 (14 years) was 351,824 papers and 48,448 patents, with a patent/paper ratio of 0.137.
Similar research is accomplished here for the period of 2000–2010, and, in the below figure, the number of references for the search term “carbon nanotubes” is shown. It must be mentioned in such a search that there are two numbers. The first one shows the document containing the exact term “carbon nanotubes”, while the second number indicates the number of references containing the concept of “carbon nanotubes”. In the given analysis, the second number containing the concept of the search term is used for the review. From the explored search under the given topic, the total number of publications for the period of 2000–2010, at a recorded date and time, is 52,224 papers. For the same period, the total number of accepted patents is 5746 items. The ratio of published patents to papers for this period is 0.11. As can be seen in the given Fig 2.1, the number of publications in journals in the year 2000 is 980, while it is increased to 8930 in 2010. An annual increase rate of 8.09% (722.72) is noted for this period. On the other hand, for the referenced patents in year 2000, the number is only 48, which is increased to 1067 in the year 2010. For the referenced patents, an annual increase of 8.68% (92.63) is obtained for this recorded period. As a result, a sharp growth in the number of referenced journal papers and filed patents is observed for this period. However, the growth rate for the patents is higher than that of the published papers in the journals.