Outer surface modification

Although outer-surface modification of carbon nanotubes has been developed for nearly two decades, interior modification via covalent chemistry is still challenging due to the low reactivity of the inner-surface. Specifically, forming covalent bonds at inner walls of carbon nanotubes requires a transformation from sp to sp hybridization. The formation of sp carbon is energetically unfavorable for concave surfaces. Hence, the interior functionalization of carbon nanotubes remains a challenge. 

Anotlier important modification metliod is tire passivation of tire external crystallite surface, which may improve perfonnance in shape selective catalysis (see C2.12.7). Treatment of zeolites witli alkoxysilanes, SiCl or silane, and subsequent hydrolysis or poisoning witli bulky bases, organophosphoms compounds and arylsilanes have been used for tliis purjDose [39]. In some cases, tire improved perfonnance was, however, not related to tire masking of unselective active sites on tire outer surface but ratlier to a narrowing of tire pore diameters due to silica deposits. 

The covalent methods previously discussed for fullerene modification using cycloaddition reactions also can be applied to carbon nanotubes. This strategy results in chemically linking molecules to the graphene rings on the outer surface of the cylinder, resulting in stable... 

Encapsulation of other material into carbon nanotubes would also open up a possibility for the applications to electrodevices. By applying the template method, perfect encapsulation of other material into carbon nanotubes became possible. No foreign material was observed on the outer surface of carbon nanotubes. The metal-filled uniform carbon nanotubes thus prepared can be regarded as a novel onedimensional composite, which could have a variety of potential applications (e.g novel catalyst for Pt metal-filled nanotubes, and magnetic nanodevice for Fe304-filled nanotubes). Furthermore, the template method enables selective chemical modification of the inner surface of carbon nanotubes. With this technique, carbon... 

Every hormone must have one or more receptors, most of which are proteins. These may be found embedded in the outer surface of the plasma membrane, in the cytoplasm, or in the cell nucleus. Binding of a hormone to its receptor often elicits both a rapid response and a slower one. For example, we have seen that glucagon, adrenaline, and vasopressin bind to cell surface receptors and promote the synthesis of cyclic AMP (Fig. 11-4). Tire cAMP induces rapid chemical modifications of many proteins. Some of these may diffuse into the nucleus and affect transcription of genes, a slower response. Insulin (Chapter 11, Section G) also exerts both rapid and slower responses. 

Chemical modification of CNTs changes or improves their chemical and electrical properties, thereby expanding their application fields. All of the efforts for the chemical modification have been directed toward the outer surface of CNTs. No one has, however, attempted to differentiate between the outer and inner surfaces or to modify only the inner one while leaving the outer one as it is. One of the reasons for this is that both ends are generally closed for most CNTs, but even if they were open, such differentiation would be essentially impossible any chemical treatment to the inner surface always affects the outer one. Only the template technique enables such selective chemical modification of the inner surface of nanotubes. With this technique, CNTs with outer and inner surfaces that have different properties can be prepared, and unique adsorption behaviors and electrical properties can be expected from such CNTs with heteroproperties. 

Discuss the modifications to the program for developing flow in a pipe that are necessary to allow it to calculate developing flow in an annulus when the inner and outer surfaces of the annulus have diameters of D, and Z>0, respectively, and when both the inner and outer surfaces are kept at the same uniform temperature. 

As noted above, one of the most important attributes of a nanombe is that it has distinct inner and outer surfaces that can be differentially chemical and biochemically functionalized. The template method provides a particularly easy route to accomplish this differential functionalization. The details of nanombe modifications using differential silane chemistry on nanombes are available elsewhere [4]. In the following paragraphs, we briefly describe the results of differential-functionalized nanombes and their applications in highly selective chemical and biochemical extractions [2,4]. 

Non-contact atomic force microscope (AFM) and N2 absorption measurements on beta zeolites reveal the extreme irregularity of the external crystal surface which can make up a considerable proportion of the total surface area. A catalytic test, the acylation of 2-methoxynaphthalene, shows that active sites on the outer surface play an important role in the catalytic activity of the zeolite. Attempts to influence the external surface area and its catalytic activity through synthesis or post-synthesis modification such as dealumination show that the principle influence on the external surface comes from the synthesis procedure. 

The grafting on both outer surface and inner surface of mesoporous silica can be done separately. First, by modifying the outer surface with as-made material, then removing surfactant and getting the inner surfactant available. The second modification is carried out on the outer surface-modified mesoporous material. This method can result in two different functional-group-modified materials.[222]... 

Mesoporous silicas with various pore sizes are hydrophobic by silylation with silanes. Changes in the pore structure as a result of the silylation reactions are monitored in order to assess the distribution of the hydrophobic groups. Extensive polymerization of dimethyldi-chlorosilane causes blocking of the micropore fraction. For silica with pore sizes in the supermicroporous range (2nm), this leads to hydrophobization of almost exclusively the outer surface. While for trimethylchlorosilane a smaller number of molecules react with the surface, modification is more homogeneous and an open structure is optimally preserved. Both silanes lead to lower surface polarity and increased hydrothermal stability, i.e., preservation of the porous structure during exposure to water.12231... 

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