Nanowires, Nanorods, and Nanofibers

Several nanoparticles having a non-spherical shape have been synthesized, e.g., carbon nanotubes, nanofibers, nanorods, and nanowires which exhibit, similar to asbestos, a fibrous shape. 

As revealed by FTIR and UV-Vis spectra in other studies, all PANI nanotubes, nanofibers, nanowires, nanorods, as well as microtubes, have backbone structures similar to that of the conventionally prepared granular PANI. In some cases, the Einstein shifts observed in the FTIR and UV-Vis spectra were ascribed to the interaction between the PANI chains and some small molecules, such as ethanol rather than to the chemical structures. 

PANI would be typically functionalized with selected dopants via either noncovalent or covalent approaches. In addition, nanostructured PANI materials, such as nanorods, nanowires and nanofibers, offer the possibilities to improve the performance of the PANI-based devices (Huang et al., 2003). PANI has demonstrated its biocompatibility in vivo and sparked great interests in tissue engineering. The biocompatibility of PANI can be further improved by the introduction of biocompatible elements without sacrificing its electric conductivity. 

One-dimensional (1-D) nanomaterials have been extremely appealing in terms of their high specific surface area, effective ion diffusion/electron transfer pathways, and good contact with electrodes or current collectors compared to bulk materials [5]. Therefore, 1-D nanomaterials with a variety of morphologies, such as nanowires, nanorods, nanotubes, and nanofibers, have been proposed as prospective separators or electroactive materials in energy storage and conversion applications... 

The range of Ti02 ID material (nanorods, nanofibers and nanowires) which have been reported in the literature is therefore increasing exponentially, although their characteristics in relation to catalytic applications are not always clear. It is also surprising the still very limited effort to use these materials for preparing catalysts. The few attempts to use them as photocatalysts should deserve further attention. 

During the past few years, a significant effort has been directed towards the synthesis of low-dimensional Mn02 nanostructures with controlled morphologies. For instance, a-, P-, y-, 6-, k-, and E-Mn02 polymorphs were synthesized in the shape of nanorods [141-145], nanowires [144, 146-148], nanofibers [149, 150], nanoneedles [151, 152], and nanotubes [153, 154]. Lately, the attention of a considerable number of chemists and materials scientists has also been oriented towards the self-assembly of 1-D nanostructured manganese dioxides into 2- and 3-D ordered microstructures [144, 155-158]. 

Conventional polyaniline has been previously used as a chemical sensor but has been limited in its sensitivity and time response. Previous work on enhancing the detection capabilities of polyaniline has included the use of thinner films (6). The disadvantages of this method are the loss of robustness of the film and the difficulty in making such thin films with good control. Another way to increase sensitivity to gases is to change the morphology of the polyaniline. In particular, nanostructured forms of polyaniline, such as nanowires, nanofibers, or nanorods, have recently received much attention because their small diameters are expected to allow for fast diffusion of gas molecules into the structures (7). 

A nanorod is typically a crystalline 1-D nanostructure, with an overall length comparable to its width (i.e., both dimensions are <100 nm). As their name implies, another feature of nanorods is their rigid sidewall structures. However, since crystalline nanorods exhibit the same overall shape as needle-like bulk crystals, the term nanocrystal is probably more appropriate for these structures (or, more explicitly rod-like nanocrystals ). Whereas nanowires, nanofibers, and nanotubes exhibit an interwoven array, nanorods are completely linear in morphology. As such, nanorods are capable of stacking onto each other to yield interesting 2-D and 3-D arrays - not usually as easy to perform with the spaghetti-like morphology of the other 1-D nanostrucmres. 

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