Size reduction, carbon nanotubes

Purification, Opening, and Size Reduction of Carbon Nanotubes by Oxidative Treatments... 

Figure 11.8 Formation of ordered nanoparticles of metal from diblock copolymer micelles, (a) Diblock copolymer (b) metal salt partition to centres of the polymer micelles (c) deposition of micelles at a surface (d) micelle removal and reduction of oxide to metal, (e) AFM image of carbon nanotubes and cobalt catalyst nanoparticles after growth (height scale, 5 nm scan size, lxl pm). [Part (e) reproduced from Ref. 47].

Recently, the efficacy of LDHs as catalyst precursors for the synthesis of carbon nanotubes via catalytic chemical vapor deposition of acetylene has been reported by Duan et al. [72]. Nanometer-sized cobalt particles were prepared by calcination and subsequent reduction of a single LDH precursor containing cobalt(II) and aluminum ions homogeneously dispersed at the atomic level. Multi-walled carbon nanotubes with uniform diameters were obtained. 

Co-MCM-41 catalyst in H2 at temperatures up to 993 K. It is this intermediate species that preserves the tetrahedral environment in the silica framework and provides the resistance to complete reduction to the metal in the presence of H2. The Co(II) species is resistant to reduction in pure CO the intermediate Co(I) species is more reactive in CO, likely forming cobalt carbonyl-like compounds with high mobility in the MCM-41. These mobile species are the precursors of the metal clusters that grow the carbon nanotubes. Controlling the rates of each step of this two-step reduction process is a key to controlling the sizes of the cobalt metal clusters formed in the cobalt MCM-41 catalysts. 

The small probe size allows the selection of an individual nanostructme and reduction of the background in the electron diffraction pattern from the surrounding materials. An example is given in Section 3.5 for the stmctme characterization of individual carbon nanotubes (CNT) by electron diffraction. 

A reduction of the required energy could be reached by the incorporation of conductive fillers such as heat conductive ceramics, carbon black and carbon nanotubes [103-105] as these materials allowed a better heat distribution between the heat source and the shape-memory devices. At the same time the incorporation of particles influenced the mechanical properties increased stiffness and recoverable strain levels could be reached by the incorporation of microscale particles [106, 107], while the usage of nanoscale particles enhanced stiffness and recoverable strain levels even more [108, 109]. When nanoscale particles are used to improve the photothermal effect and to enhance the mechanical properties, the molecular structure of the particles has to be considered. An inconsistent behavior in mechanical properties was observed by the reinforcement of polyesterurethanes with carbon nanotubes or carbon black or silicon carbide of similar size [3, 110]. While carbon black reinforced materials showed limited Ri around 25-30%, in carbon-nanotube reinforced polymers shape-recovery stresses increased and R s of almost 100% could be determined [110]. A synergism between the anisotropic carbon nanotubes and the crystallizing polyurethane switching segments was proposed as a possible... 

From 100 rpm to 800 rpm, the reduction in agglomerate size is considerable and this is observable as the temperature rises after microwave irradiation. High screw speeds result in low agglomerated structures and higher microwave effectiveness. Nevertheless, excessive shear forces can provoke carbon nanotube fracture and thus limit the heating efficiency. 

In the UK, researchers at Cambridge University have devised a method of growing vertical carbon nanotubes on a flexible plastic substrate which gives scope for further research into potential applications especially where flexibility is a key element of the product design. At Sheffield University the research project involves the dispersion of nano-sized droplets of PEDOT (or other conducting polymers) into a polyethylene oxide polymer electrolyte matrix. Together with a suitable redox couple, where oxidation and reduction are considered together as complementary processes, it is possible to produce efficient, switchable windows for microwaves. 

In addition, Xin et al. [115] prepared multiwalled carbon nanotube-supported Pt (Pt/MWCNT) nanocomposites by both the aqueous solution reduction of a Pt salt (HCHO reduction) and the reduction of a Pt ion salt in ethylene glycol solution (EG). For comparison, a Pt/XC72 nanocomposite was also prepared by the EG method. The Pt/MWCNT catalyst prepared by the EG method has a high and homogeneous dispersion of spherical Pt metal particles with a narrow particle-size distribution. 

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