Self-assembly, hydrothermal syntheses

Porous materials with chemically modified surfaces have been extensively studied as adsorbents for heavy metal ions from water (see the review by Jal et al.2 and references therein). There is a continuously growing demand for adsorbents which are non-swelling, thermally and hydrothermally stable, exhibit large adsorption capacity, fast kinetics and high affinity towards heavy metal ions. Discovery of self-assembled ordered mesoporous silicas (OMSs)3 opened enormous opportunities for the design and synthesis of highly selective and efficient adsorbents for heavy metal ions. 

Supported zeolite membranes have been prepared using numerous procedures [4] such as alignment of crystals in electrical fields, electroplating, self-assembly, growth on organic molecular layers, covalent linkages, hydrothermal synthesis (in situ and ex situ), hydrothermal method microwave heating assisted, dry gel method (vapor-phase transport method and steam-assisted crystallization), synthesis at the interface between two fluid phases, etc. 

Other promising routes to preparing new kinds of efficient materials include molecular self-assembly, adaptative supramolecular and dynamic chemistry, and hydrothermal synthesis for zeolites [8-10]. 

Conversions of nanosheets into nanorods have been possible for metal oxides such as ZnO (44). The self-assembled nanosheets arc first prepared by a solution phase hydrothermal synthesis. The reactant solution eontains zine nitrate, hexamethylene tetra-mine and hydrazine, whieh helps in the fonnation of precursor nanosheets in an orderly fashion. At shorter time seales ( 46), nanosheets are formed and after 8 h, hollow microspheres arc formed. The nanosheets arc calcined at 400°C to get ZnO nanorods, as depicted in Figure 7.6. This is an example where one nanostmcture transforms to a completely different morphology. 

FePt nanorods of high quahty have been produced by decomposition of Fe(CO)5 and reduction of Pt(acac)2 in a confined cyUndiical mesophase consisting of surfactants such as oleic acid and oleyl amine at high concentrations and slow heating (61). Self-assembly of FePt nanorods can be carried out on a silicon wafer by evaporating a hexane dispersion. Hydrothermal synthesis has also been used for self-assembly by precoating the substrate with aluminum metal (62). Under hydrothermal conditions, the aluminum metal transforms to a hydrotalcite-like phase which provides a lattice matched substrate for the growth of oxide nanorods such as ZnO (Fig. 7.12). The substrates can be diverse, flat, or curved, such as silicon, polystyrene beads, carbon nanotube array, etc. 

The synthesis of M41S-type materials can be carried out under hydrothermal conditions using alkyltrimethylammonium cations C TMA" as structure-directing agents and tetraethoxysilane (TEOS) as silica source. Similarly to the lyotropic phases formed in surfactant-water mixtures, the surfactants form micellar structures. Their self-assembly is strongly influenced by the presence of silicate anions which form by the hydrolysis of TEOS. After the synthesis, the space in between the surfactant micelles is filled by silica which develops by polycondensation of the silicate anions and which forms walls of a thickness of ca. 8 A [3,4]. 

The fifth chapter presents detailed review of technological aspects of ferroic nanoparticles fabrication. We present the detailed information about methods of chemical synthesis of above nanoparticles. Among them are hydrothermal, sol-gel and coprecipitation methods. We also present the method of unstable compounds decomposition. The combined synthesis methods have also been discussed. Namely, we consider mechanochemical, sonochemical and template synthesis methods. The main idea of these methods is to control the dispersity and agglomeration degree of nanoparticles by inspection of nucleation and growth of a new phase. Self-assembly and self-organization of ferroic nanoparticles as well as composites formation on their base by means of colloidal processes have also been considered. 

RuOj nanotubes have been synthesized by the thermal decomposition of Ru3(CO)j2 inside anodic alumina membranes [248]. Transition metal oxide nanotubes have been prepared in water using iced hpid nanotubes as the template [249]. Self-assembled cholesterol derivatives act as templates as well as catalysts for the sol-gel polymerization of inorganic precursors to give rise to double-walled tubular structures of transition metal oxides [250]. Hydrothermal synthesis of single-crystalline y-Fefi ... 

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