Applications pore architectures with

Since their discovery, microporous materials such as zeolites found major application fields in processes like separation, ion exchange and catalysis. Their uniform pore size and pore architecture are at the basis of separation processes whereas the chemical composition of these materials makes them unbeatable candidates to be used as a catalyst or an ion exchanger. Regardless of which process is used, the molecules engaged are adsorbed on the surface according to their molecular structure and properties. The bulkiness of the molecule compared to the pore size of the microporous material decides if or not the molecule can be trapped in the depth of the porous framework, thus there exists cases where molecules with larger diameters than the pore size are not able to enter the pores. This makes the microporous materials acting as a sieve in molecular level and they are hence referred to as molecular sieves. 

One of the main advantages of application of zeolitic or other porous materials is the shape-selectivity of this type of material, which arises due to differential diffusion of molecules with different sizes and shapes in the zeolitic or other porous materials. Iherefore, it is very instructive to monitor the pore architecture directly, with a molecule that "observes" the zeolitic type of structure. 

This chapter considers the fabrication of oxide semiconductor photoanode materials possessing tubular-form geometries and their application to water photoelectrolysis due to their demonstrated excellent photo-conversion efficiencies particular emphasis is given in this chapter to highly-ordered Ti02 nanotube arrays made by anodic oxidation of titanium in fluoride based electrolytes. Since photoconversion efficiencies are intricately tied to surface area and architectural features, the ability to fabricate nanotube arrays of different pore size, length, wall thickness, and composition are considered, with fabrication and crystallization variables discussed in relationship to a nanotube-array growth model. 

As an example of hybridization of zeolites with cellulose derivatives, self-supporting zeolite membranes with a sponge-like architecture and zeolite microtubes were prepared by using CA filter membranes as a template [154]. The hierarchical structure with sub-nanometer- to micrometer-sized pores is a characteristic of great promise for a wide range of applications such as catalysis, adsorption, and separation. There was also an attempt to prepare alginate membranes incorporated with zeolites, e.g., for pervaporation separation of water/acetic acid mixtures [155]. 

Another variation on the theme of quenched disordered structures noted in Section ILA is to employ a removable template such as an organic molecule, colloid, or metal ion during the synthesis of a porous material [52-54], Following formation of the quenched material structure, as shown in Fig. 7, the template is removed, leaving behind a matrix of particles with a pore space that mimics, to some extent, the original template. Because templates of diverse size and shape are available, templating offers the prospect of designing porous materials whose architectures are tailored for specific applications. 

Table II (118) shows that the surface area, pore volume, and pore size of the deposited films vary consistently with the aging times. Thus the film structures may be tailored for such applications as surface passivation, sensors, membranes, or catalysts by a simple aging process prior to film deposition. In addition, multiple deposition schemes involving different compositions or structures or both allow the formation of complex layered architectures potentially useful for optics, electronics, or sensors.

---