Nanoparticle Assembly with Templates

J-Z.Xu, S. Xu, J. Geng, G-X. Li, J-J Zhu, The frabrication of hollow spherical copper sulfide nanoparticles assemblies with 2-hydroxypropyl-b-cyclodextrin as a template under sonication. Ultrasonic Sonochemistry, 13 (2006) 451-454. 

In fact, such biomimetic molecules demonstrate the ability to tailor the growth of silica nanoparticles in a way that is very similar to diatom-extracted species. However, they demonstrate the same limitations in terms of morphological control of nanoparticle assembly. This is because the diatom shell architecture results not only from interactions of silica precursors with templating molecules but also benefits from a cell-driven molding of the vesicular compartment where silicification occurs [29]. Thus, it is very likely that diatom-like synthetic silica will only be achieved when such confinement/molding effects are taken into account in the design of biomimetic experiments [30]. 

Figure 6.8 Illustration of colloid-templated nanoparticle assemblies. The process involves the layer-by-layer adsorption of charged polymers and oppositely charged nanoparticles onto the surfaces of the colloidal template. The colloidal core particles may then be removed to generate a hollow sphere of nanoparticles, held together by electrostatic interactions with the linear polymer glue ...

Synthesis of Si02- and Ti02-nanoparticles hybrids with MWCNTs has also been reported (Fig. 3.19) the reaction proceeds by means of phosphonic acid-modified and alkoxy silane-modified CNTs which can cap the oxides and template their assembly onto the CNT s surface [99]. 

Increasingly chemists are contributing to the synthesis of advanced materials with enhanced or novel properties by using colloidal assemblies as templates. Colloid chemistry is particularly well suited to this objective since nanoparticles, by definition, are colloidal and since processing of advanced materials involve reactions at solid-solid, solid-liquid or solid-gas interfaces (3-5). 

Figure 12.25 (a) Assembly of a Au nanoparticles wire in the poly A/polyT template using Au nanoparticles functionalized with intercalator (psoralen) molecules, (b) AFM image of the Au nanoparticles wire in the poly A/polyT template. Reproduced with permission from Ref. 91. Copyright Wiley-VCH Verlag GmbH Co. KGaA. 

Miscellaneous Soft-Template Methods Novel Y-junction PANI-NTs, accompanied with nanorods, have been selectively prepared using in situ self-assembly of water-soluble Fe304 nanoparticles coated with PEG(5)-nonylphenylether and cyclodextrin as templates and pH control in an aqueous medium [373]. A chemical oxidative route to synthesize oriented arrays of conducting PANI-NTs in HCl solution by hydrogen-bonding directionality in the presence of a crown ether derivative (CE-SO3K) has also been reported [374]. 

Another approach to introduce mesoporous channels to give better access of reactant molecules to the microporous regions is to assemble zeolite nanoparticles around micellar templates, in a modification of the standard route to mesoporous silicas. Reported examples include structures that possess walls made out of nanocrystals of zeolites such as Beta or ZSM-5. These composite solids possess enhanced hydrothermal stabilities and acidities compared to mesoporous solids with fully amorphous walls. The improved properties are attributed to the presence of the zeolite fragments, because zeolites are known to have higher acidity and hydrothermal stability than amorphous silica/... 

Viruses are similar to biomolecular templates because the viral capsid is in fact a complex composed of protein subunits. Viruses coupled with nanoparticles can be used as building blocks to form nanoparticle assemblies or virus assemblies of two and three dimensions can be used as templates. Virus is advantageous as a building block because identical viruses can be produced in large amounts at low cost, and nanoparticles templated by viruses generally have a high monodispersity. Viruses may have inherent self-assembly, for example, nanowires mineralized... 

Fig. 6 Schematic illustration of the use of a living hypha of a filamentous fungus as the template for the assembly of oligonucleotide-functionalized Au nanoparticles into ordered microscopic structures, (a) As the living fungal hypha grows, the Au nanoparticles (functionalized with single-stranded DNA) bind to its cell walls, and a microscopic tube-shaped nanoparticle assembly is formed, (b) Additional layers of nanoparticles...

Kondo et al. reported a novel fabrication method of polymer nanotubes by combination of an alternate layer-by-layer (LbL) assembly of PLLA and PDLA and the siliea template method. Silica nanoparticles with a diameter of 300 nm were alternately immersed in aeetonitrile solutions of PLLA and PDLA at 50 °C. The immersion process was performed for 10 cycles to deposit 10 double layers of PLLA and PDLA. The resulting partieles were then treated with 2.3% aqueous hydrofluoric acid to remove the siliea core. The hollow eapsules have a spherical shape with a diameter of 320 nm and a shell thiekness of approximately 60 nm. Tubular assemblies with an average diameter of 300 nm and lengths of 2-5 pm are obtained by evaporating water at ambient temperature from a water dispersion of the hollow eapsules on a polyethylene terephthalate (PET) substrate. 

Fig. 18 Concept of DHBCs, their interaction with mineral surfaces and possibilities for particle stabilization or self-assembly, a Nanoparticle stabilization, b unordered particle aggregation, c oriented attachment, d ordered aggregation/mesocrystal formation, e arrangement of nanoparticles around a template. Reproduced from [151] with permission of the Materials Research Society...

---