Gels as Templates

For the cholesterol derivatives 22 and 23 the transcription into hollow fiber silica occurred even in the absence of metal salt additives. This phenomenon was ascribed to the protonation of the monoaza- and diaza-18-crown-6 moieties due to their relatively high pA a values, thus providing under the sol-gel polymerization conditions the required cationic charges for the stimulation of the transcription effect. 

Tubular shaped superstructures formed by certain amphiphiles in water aggregate through intermediate helical ribbon structures.Since these amphiphiles feature a polar head in combination with a chiral hydrophobic group, the sol-gel 

The tubular structure was observed both by TEM and SEM whereas the granular structure was observed only by SEM 

However, the use of organogel superstructures for the creation of silica with novel morphologies is not only limited to fiber shaped structures. Due to their potential applications as adsorption media, molecular sieves and catalysts, the design of spherical mesoporous silica has been of special interest. Pioneering work in this area was done by Ozin et al with the synthesis of a lamellar alu-minophosphate phase in solution containing vesicles formed from tetraethylene 

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Low temperature sol-gel technology is promising approach for preparation of modified with organic molecules silica (SG) thin films. Such films are perspective as sensitive elements of optical sensors. Incorporation of polyelectrolytes into SG sol gives the possibility to obtain composite films with ion-exchange properties. The addition of non-ionic surfactants as template agents into SG sol results formation of ordered mechanically stable materials with tunable pore size. 

Gel-Type Cross-Linked Functional Polymers as Template in the Synthesis of Size Controlled Metal... 

Fe-TON (Fe-ZSM-22) zeolites of different Si/Fe ratios (27, 36, 50, and 150) were synthesized hydrothermally using 1-ethylpirydinium bromide (EtPBr) as template. The syntheses were carried out following the procedure reported in Ref [7]. The molar composition of gels used for the syntheses was ... 

The hydrothermal synthesis of MCM-22 precursor was performed under static conditions, from a gel having the ratio Si02/Al203 = 30 and hexamethyleneimine as template [7]. The resulting precursor has been divided into two parts one part was... 

The deposition of nanostructured Ti02-based material directly on glass is expected to achieve enhanced photocatalysis and mechanical strength. Sputtering and a combination of sputtering and sol-gel techniques seem to be the most adequate for such a purpose [91,97,98], In the latter case, porous alumina Trims on glass formed by anodizing sputter-deposited A1 layers were used as templates in the successive sol-gel process. 

The advent of the addition of a quaternary ammonium cation as template or structure directing agent (SDA) to the alkaline gel by Barter and coworkers, and Mobil Oil coworkers, led to the Si02 enriched zeolite A in the case of Barter and to the high silica zeolites. Beta and ZSM-5, by the Mobil group. The latter synthesis temperature typically is 100-200 °C, higher than Milton s original work. 

Metal oxide nanotubes have been synthesized by a diverse variety of fabrication routes. For example titania nanotubes, and nanotube arrays, have been produced by deposition into a nanoporous alumina template [48-51], sol-gel transcription using organo-gelators as templates [52,53], seeded growth [54], hydrothermal processes [55-57] and anodic oxidation [58-65]. 

Tamaru S, Takeuchi M, Sano M, Shinkai S (2002) Sol-gel transcription of sugar-appended porphyrin assemblies into fibrous silica unimolecular stacks versus helical bundles as templates. Angew Chem Int Ed 41 853-856... 

Si02 gel DDAB/toluene/water (48.7% DDAB, 19.5% decane, 31.8% aqueous silica sol) TMOS (partially hydroiyzed)/H20 (+ 0.4-10 wt%HF) Bicontinuous p,Es used as templates for microporous silica gels monodisperse pores (2 nm pore radius) large specific surface area (—103 m2/g) (51)... 

The work of Mallouk et al. (39) offers an interesting extension of the microemulsion sol-gel technique. In this case, microemulsion-derived silica nanoparticles were used as templates for preparing ordered mesoporous polymers with tailored pore sizes. Utilizing the Triton N-101/cyclohexane/hexanol/water/ammonia microemulsion, monodisperse silica nanoparticles were first synthesized. The silica product... 

This study demonstrated that the micro-mesoporous composite materials could be synthesized with two-step treatment by microwave using two different templates system with TPABr and MTAB. This formation was controlled by the self-assembly formation of supramolecular templates between MTA micelles and SiO /TPA gels. As varying microwave irradiation time of micro-mesoporous materials, gradually transition from the mesophase to micro-mesophase was occurred. These materials have higher dm spacing of mesoporous materials and lead to transition from mesophase to micro-microphase by an increment of synthetic time, while the calcined products is formed with bimodal and trimodal pore size distribution under microwave irradiation within 3 h. From TG-DTA and PL analysis, the self-assembly formation of supramolecular templates between MTA+ micelles and SiO /TPA+ gels were monitored. 

Another example of the sensitivity of 13C MAS NMR to zeolite structure is the work of Jarman and Melchior (331) who could distinguish between TMA+ cations trapped in the ol and / (sodalite) cages in zeolite A structure in the course of crystallization from a precursor gel. If, therefore, the zeolite which is to be analyzed by 13C NMR, so as to evaluate the extent of intergrowth or variable cage environments is synthesized using TMA + cations as templates, then this method, as we show below, seems viable. 

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