Inorganic Layer Templating Routes

Inorganic layers can be used as a sacrificial template that can be removed by chemically dissolving it in an aqueous solution to form a nanotube structure. It is advantageous to form metal and polymer nanotubes if the nanotubes are not chemically influenced by the template etchant. ZnO nanorods are a typical example of an inorganic template used during the preparation of nanotube structures [80-82]. The fabrication of Pt nanotubes using ZnO nanorod 

In addition, polymeric nanotubes, that is, polypyrrole (PPy) nanotubes, using ZnO sacrificial nanorods were demonstrated by Wang et al. ZnO nanorod arrays were prepared by electrodeposition in a solution of Zn(NOs)2 (0.01 M) and NH4NO3 (0.05 M) at 70 °C for 90 min with a current density of 1mA cm . Then, the electropolymerization of PPy was performed in a solution of pyrrole (0.1 M) and Na2 04 (0.05 M) at 70 °C for 30 min with a current density of 2 mA cm thereby forming a ZnO/PPy core-shell nanotube array structure. Finally, 

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Through a co-assembling route, mesostructured lamellar molybdenum sulfides are formed hydrothermally at about 85 °C using cationic surfactant molecules as the templates. The reaction temperature and the pH value of the reaction system are important factors that affect the formation of the mesostructured compounds. The amount of the template and that of the S source are less critical in the synthesis of the compounds. For the three as-synthesized mesostructured materials, the interlayer distance increases linearly with the chain length of the surfactant. Infrared and X-ray photoelectron spectroscopy reveals that the individual inorganic layers for the three compounds are essentially the same both in composition and in structure. The formal oxidation state of the molybdenum in the materials is +4 whereas there exist S2 anions and a small amount of (S-S)2 ligands in the mesostructures. The successful synthesis of MoS-L materials indicates that mesostructured compounds can be extended to transition metal sulfides which may exhibit physico-chemical properties more diverse than non-transition metal sulfides because of the ease of the valence variation for a transition metal. 

The separation layer, either porous or dense, can be formed using different methods such as sol-gel and template routes, hydrothermal synthesis, chemical vapor deposition (CVD), or physical sputtering, depending on the membrane material and its application. These membrane preparation methods will be described in the following chapters of this book for different membranes and membrane reactors. We note that the preparation of inorganic membranes involves a multi-step high-temperature treatment process. Therefore, inorganic membranes are much more expensive than polymeric ones. 

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