Hard-Templated Growth

The hard-templating growth methods described before should not be confused, on the contrary, with soft-templating approaches which usually are accomplished in solution phase in the presence of free surfactant molecules which severely attend the nucleation of a new particle and the further shape development selectively and dynamically interacting with the evolving particle surface facets. 

---

Hard Templating by Carbon Materials The work on carbon templating by Jacobsen and coworkers [156] has stimulated dramatic growth in the synthesis of mesoporous/hierarchical zeolites. This approach uses an excess of zeolite gel inside an inert, mesoporous carbon matrix, wherein the zeohte grows over and... 

However, the formation of mesophases inside the two-dimensional confinement of nanopores can be complex. For example, a model compound based on the triphenylene motif was melt-infiltrated into AAO hard templates. It was found that homeotropically anchored columns whose growth starts from the pore walls compete with planar columns in the center of the pores that proceed along the pore axes, i.e., along the direction that is free... 

Martin [21] proposed a mechanism for the growth of the nanostructures prepared by the hard-template method. However, the mechanism is insufficient in explaining the growth of partially filled nanotubes by an electrochemical template synthesis [36]. Recently, Lee and coworkers [37] investigated the electrochemical... 

There also existed another use of synthetic polymers besides synthetic gels as the hard template to influence crystal growth discussed above. In this case, sohd synthetic polymers were used as a real hard template . It has been demonstrated that calcium carbonate favored the formation of the vaterite phase on the poly(vinyl chloride-co-vinyl acetate-co-maleic acid) substrate in the supersatiuated solution prepared from calcium nitrate and sodium dicarbonate solutions at pH 8.50 [238]. Commercial polymer fiber (Nylon 66 and Kevlar 29) can induce crystallization of calcite in solution, but the vaterite phase tends to crystallize on the surface of polymers in the presence of soluble polymer (PVA), and aragonite favors forming on the siuface of polymers modified with acid or alkah accompanying PVA [239]. 

A number of methods, such as hard and soft template as well as physical methodologies have been used to synthesize conducting polymer nanostructures. In the hard template method, a template membrane is usually required to guide the growth of... 

A hard template can restrict the growth of nanomaterials by spatial confinement. To grow ID nanomaterials, anodic aluminum oxide (AAO) is a commonly used hard template with uniform hex-agonally ordered channels. Assisted by the capillary driving force, the precursors diffuse into the channel. After precipitation by a base or simple hydrolysis by heating, the ID nanostructure can form. ... 

To better control the ordering of mesopores in the silica shell, along with particle size and shape, the hard template method in combination with surfactant templating has been studied intensively. Typically, hollow particles with hexagonally ordered mesoporous shells can be obtained by using PS beads and CTAB in an aqueous ammonia solution. After the growth of a silica-surfactant meso-structured composite shell on the surfeice, the PS template is finally removed by calcination to form hollow spheres. Several reports have succeeded in... 

This is a powerful and controllable method to synthesize the nanostructure materials of inorganic semiconductors, metals, and polymers. In the hard template method, the growth of the nanostructures takes place within the pores or channel of template membrane by polymerization and then the template is removed after the polymerization. The porous membrane is the basic and most important part of the hard template method. Porous membrane such as polycarbonate and alumina can be used as the hard template to produce conducting polymer nanotubes and nanowires as shown in Fig. 9. 

In the absence of a hard template, solntion-based methods for the synthesis of NPs require precise tuning of nucleation and growth steps to achieve crystallographic control. These reactions are governed by thermodynamic (e.g., tanperatme and rednction potential) and kinetic (e.g., reactant concentration, diffusion, solubility, and reaction rate) parameters, which are very well linked. Thus, the exact mechanisms for shape-controlled colloidal synthesis are often not well understood or characterized. 

---