Preparation of CNTs

The preparation of CNTs is a prerequisite step for the further study and application of CNTs. Considerable efforts have been made to synthesize high quality CNTs since then-discovery in 1991. Numerous methods have been developed for the preparation of CNTs such as arc discharge, laser vaporization, pyrolysis, and plasma-enhanced or thermal chemical vapor deposition (CVD). Among these methods, arc discharge, laser vaporization, and chemical vapor deposition are the main techniques used to produce CNTs. 

Li et al. [52, 53] have reported the preparation of CNTs-modified GCE by casting the GCE with 15 pL of a SWCNTs suspension (armchair structure, prepared by arch-discharge and purified by oxidation in air) in DMF (O.lmg/mL). The drying step was performed under an IR heat lamp. 

Protease-free preparation of CNTs can be obtained using an immobilized-metal-ion affinity chromatography (IMAC) step (Ros-setto et a/., 1992). This procedure is also useful for the purification of He, the 50 kDa carboxy-terminal part of the heavy chain of TeTx, which shows an identical retention time. However, IMAC-chromatography cannot be used for the purification of BoNT/D because this serotype is not retained. To obtain a protease-free BoNT/D preparation, an ion-exchange chromatography procedure was used (Schiavo and Montecucco, 1995). After freezing in liquid nitrogen, purified CNTs are stored at -80°C. 

Figure 12. Procedure for the preparation of CNT-PAMAM and GOx-HRP immobilized CNT-PAMAM (Adapted from Ref. [141]).

The oxidative procednre of CNTs alone may generate a stable CNT suspension which can be used for the preparation of CNT coated electrodes. Other procedures to prepare CNT suspensions are based on non-covalent stabilization of CNTs by using either surfactants or polymers. An excellent review on this subject has been published... 

Pillai, S. K., Ramontja, J., and Ray, S. S. (2011). Amine functionalization of carbon nanotubes for the preparation of CNT based polylactide composites-a comparative study. 

Some research on the pre-treatment of CNTs and interfacial modification techniques have been reported, which is helpful to the preparation of CNT-filled rubber composites. " But the dispersion of CNTs into rubber materials is still problematic due to possible entanglement of the high aspect ratio CNTs and the high viscosity of rubbers. 

A novel mixing method using a rotation-revolution mixer was applied to the preparation of CNTs/SBR composites. The results indicate that mixing technique can reduce the amount of CNTs needed to provide high electrical conductivity to the SBR matrix. The mixing method can be applied to various types of CNTs with SBR. For all CNTs/SBR composites, the percolation thresholds were less than 1 phr and were largely dependent on the structural quality of CNTs used as the filler material. 

Matyjaszewski et al. [2] patented a novel and flexible method for the preparation of CNTs with predetermined morphology. Phase-separated copolymers/stabilized blends of polymers can be pyrolyzed to form the carbon tubular morphology. These materials are referred to as precursor materials. One of the comonomers that form the copolymers can be acrylonitrile, for example. Another material added along with the precursor material is called the sacrificial material. The sacrificial material is used to control the morphology, self-assembly, and distribution of the precursor phase. The primary source of carbon in the product is the precursor. The polymer blocks in the copolymers are immiscible at the micro scale. Free energy and entropic considerations can be used to derive the conditions for phase separation. Lower critical solution temperatures and upper critical solution temperatures (LCST and UCST) are also important considerations in the phase separation of polymers. But the polymers are covalently attached, thus preventing separation at the macro scale. Phase separation is limited to the nanoscale. The nanoscale dimensions typical of these structures range from 5-100 nm. The precursor phase pyrolyzes to form carbon nanostructures. The sacrificial phase is removed after pyrolysis. 

An example of the preparation of CNT samples is reported on the following web site http //ndeaa.jpl.nasa.gov/nasa-nde/lommas/eap/Nanotube-PrepProcedure.htm. 

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