Other Nanoparticle Shapes

The aforementioned frequency of the use of these nanomaterial shapes is best attributed to two factors (1) the ease with which these nanoparticle shapes can be synthesized in the laboratory and (2) the availability of these nanomaterials from commercial sources. It cannot be the aim of this review to cover all of the different nanomaterials used so far, but some of the most commonly investigated will be introduced in more detail. For zero-dimensional nanoparticles, emphasis will be put on metallic nanoparticles (mainly gold), semiconductor quantum dots, as well as magnetic (different iron oxides) and ferroelectric nanoparticles. In the area of onedimensional nanomaterials, metal and semiconductor nanorods and nano wires as well as carbon nanotubes will be briefly discussed, and for two-dimensional nanomaterials only nanoclay. Finally, researchers active in the field are advised to seek further information about these and other nanomaterials in the following, very insightful review articles [16, 36-45]. 

The formation of nanoparticles from microemulsions need not essentially follow the template shape. Pileni [32] (as quoted by Ganguli and Ganguli) has shown that with water/isooctane/Cu( AOT)2 shapes like sphere to cylinder to mixed spherulites and cylinders to other polydisperse shapes were possible with increasing to. According to Pileni [33], the presence of salt anions can control the shape while chloride ions favour formation of nanorods, nitrate ions hinder it. The surfactant content also can have a say on the shape of nanoparticles. The infrequently observed morphologies of nanoparticles, viz. wires, trigons, hexagons, cubes etc. have so far no specific and reliable reasons for formation in micro emulsion templates. 

With each new shape, the nanomaterials can have different and unique chemical and physical properties that are different from the bulk material. Scientists have only just begun to make nanoparticles from a small handful of chemical elements. You can expect many new technologies to be borne out of making interesting nanoparticle shapes with other elements from the periodic table. 

Clearly, many research groups are working to understand and time the plasmonic properties of noble metal nanostructures. The relationship between the LSPR and parameters such as nanoparticle size or refractive index of the local environment is relatively straightforward. On the other hand, parameters such as nanoparticle shape or lattice spacing present more complex behavior. The theoretical work done with both... 

Current synthesis techniques provide an unprecedented level of control over nanoparticle shape and composition, resulting in an almost limitless catalog of nanoparticles with varying geometry and interactions.Examples of different shapes include spheres, rods, cubes and other polyhedra, plates, ° and multipods, along with molecular nanoparticles such as carbon fullerenes, porphyrin squares, polyhedral oligomeric silsesquioxane (POSS)... 

The shape control of nanoparticles is a very important aspect in nanotechnology, due to the spectacular effects that structural anisotropy may have on many of the material s physical properties. Because of these size- and shape-dependent properties, much effort has been expended in controlling the morphology and assembly of nanoparticles [68-69]. The most common architecture of these nanocrystals is isotropic particles, ranging from spherical to highly faceted particles, such as cubic and octahedral. One-dimensional (1-D) anisotropic nanoparticles include uniform rods and wires, whereas two-dimensional (2-D) nanoparticles consists of nanodiscs, plates and other advanced shapes such as rod-based multipods and nanostars. 

The identification of structure sensitivity would be both impossible and useless if there did not exist reproducible recipes able to generate metal nanoparticles on a small scale and under controlled conditions, that is, with narrow size and/or shape distribution onto supports. Metal nanoparticles of controlled size, shape, and structure are attractive not only for catalytic applications, but are important, for example in optics, data storage, or electronics (c.f. Chapter 5). In order not to anticipate other chapters of this book (esp. Chapter 2), remarks will therefore be confined to few examples. 

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