Carbon nanotubes synthesis process

EXAMPLE TWO-LEVEL FRACTIONAL FACTORIAL DESIGN IN A SINGLE-WALLED CARBON NANOTUBES SYNTHESIS PROCESS... 

Other technological aspects of carbon nanotube synthesis currently under scrutiny include study of the growth mechanism [67,71], attempts to control the diameter [72-74], processes which yield very long CNTs [70,75], optimization of the catalyst composition [76], and improvements in purity [77]. A major area of focus is the production of CNTs at selected sites on a substrate (micropatterning) [78-81]. Other synthetic methods investigated have been (i) a solvothermal route, in which reactants are heated in solution in a sealed autoclave [82,83] (ii) a solid-state metathesis process [84] (iii) a hydrothermal process which produces MWNTs from amorphous carbon [85] and (iv) low-temperature processes [59]. 

Terrones, M., Ajayan, P.M., Banhart, F., Blase, X., Carroll, D.L., Charlier, J.C., Czerw, R., Foley, B., Grobert, N., Kamalakaran, R., Kohler-Redlich, P., Ruble, M., Seeger, T., Terrones, H. (2002). N-doping and coalescence of carbon nanotubes synthesis and electronic properties. Applied Physics A Materials Science Processing, Vol.74, No.3, pecember 2001), pp. 355-361, ISSN 0947-8396... 

Puretzky, A.A. Geohegan, D.B. Fan, X. Pennycook, S.J. (2000). Dynamics of single-wall carbon nanotube synthesis by laser vaporization. Applied Physics A Materials Science Processing, 70,153-160. 

M. Terrones, P.M. Ajayan, F. Banhart, X. Blase, D.L. Carroll, J.C. Charlier, R. Czerw, B. Foley, N. Grobert, R. Kamalakaran, P. Kohler-Redlich, M. Ruble, T. Seeger, H. Terrones, N-doping and coalescence of carbon nanotubes synthesis and electronic properties. Appl. Phys. Mater. Sci. Process. 74(3), 355-361 (2002)... 

The aluminum is incorporated in a tetrahedral way into the mesoporous structure, given place to Bronsted acidic sites which are corroborated by FTIR using pyridine as probe molecule. The presence of aluminum reduces the quantity of amorphous carbon produced in the synthesis of carbon nanotubes which does not happen for mesoporous silica impregnated only with iron. It was observed a decrease in thermal stability of MWCNTs due to the presence of more metal particles which help to their earlier oxidation process. 

Apart from the traditional organic and combinatorial/high-throughput synthesis protocols covered in this book, more recent applications of microwave chemistry include biochemical processes such as high-speed polymerase chain reaction (PCR) [2], rapid enzyme-mediated protein mapping [3], and general enzyme-mediated organic transformations (biocatalysis) [4], Furthermore, microwaves have been used in conjunction with electrochemical [5] and photochemical processes [6], and are also heavily employed in polymer chemistry [7] and material science applications [8], such as in the fabrication and modification of carbon nanotubes or nanowires [9]. 

The approaches used for preparation of inorganic nanomaterials can be divided into two broad categories solution-phase colloidal synthesis and gas-phase synthesis. Metal and semiconductor nanoparticles are usually synthesized via solution-phase colloidal techniques,4,913 whereas high-temperature gas-phase processes like chemical vapor deposition (CVD), pulsed laser deposition (PLD), and vapor transfer are widely used for synthesis of high-quality semiconductor nanowires and carbon nanotubes.6,7 Such division reflects only the current research bias, as promising routes to metallic nanoparticles are also available based on vapor condensation14 and colloidal syntheses of high-quality semiconductor nanowires.15... 

The process begins with the synthesis of different semiconductor nanomaterials (e.g., single-walled carbon nanotubes and single-crystalline nanowires/... 

Various nanoporous AAO membranes have been obtained by varying different parameters such as applied voltage, temperature of electrolyte, electrolytic concentration and speed of rotation of electrolyte in two step anodization process. SEM analysis performed for evaluation of results. The relationship between pore size and variation of different parameters obtained. The synthesized membranes have been used as template for the synthesis of carbon nanotubes of different nano dimensions. 

Carbon nanotubes comprise a very promising material for various applications and especially as an active component in composites and hybrids as will be documented in the other chapters of this book. Harnessing these nanoscopic assets in a macroscopic material would maximize CNTs potential and applicability. The choice of synthesis technique and purification method, which define size, type, properties, quality and purity of CNTs as well as their processability, is crucial for their implementation into composites and hybrids. 

The past decade has led to the detection of new carbon allotropes such as fullerenes26 and carbon nanotubes,27 28 in which the presence of five-mem-bered rings allows planar polycyclic aromatic hydrocarbons to fold into bent structures. One notes at the same time that these structures are not objects of controlled chemical synthesis but result from unse-lective physical processes such as laser ablation or discharge in a light arc.29 It should be noted, on the other hand, that, e.g., pyrolytic graphitization processes, incomplete combustion of hydrocarbon precursors yielding carbon black, and carbon fibers30 are all related to mechanisms of benzene formation and fusion to polycyclic aromatic hydrocarbons. 

New spatial forms of carbon - fullerenes, nanotubes, nanowires and nanofibers attract significant interest since the time of their discovery due to their unique physicochemical and mechanical properties [1-3]. There are three basic methods of manufacturing of the carbon nanomaterials (CNM) - laser evaporation, electric arc process, and catalytic pyrolysis of hydrocarbons. However, the multi-stage manufacturing process is a serious disadvantage for all of them. For example, the use of organic solvents (benzol, toluene, etc.) for separation of fullerenes from graphite soot results in delay of the synthesis process and decrease in the final product quantity. Moreover, some environmental problems can arise at this. 

The carbon nanotubes up to 10-15 nm in diameter have been produced by the graphite evaporation in water. The resulting structures produced in water do not contain catalysts. This simplifies the process of their purification and reduces the net cost (Fig. 5). Varying the regime of synthesis one can produce both tubular and ribbon structures. 

The distinctive feature of the discussed method for nanostructural carbon material synthesis is that there is a possibility to produce these materials without catalysts owing to a very quick synthesis (competing with velocity of light). An example of such type of process is synthesis of carbon nanotubes by evaporation of pure graphite in liquid media. 

The synthesis processes for the nanotubes have been continuously refined in the recent years and today, a number of methods are available to synthesize both single and multiwalled carbon nanotubes. These methods include high temperature evaporation using arc-discharge (28-30), laser ablation (31), chemical vapor deposition etc. (32-34). 

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