Mesostructures, synthesis

Mesostructure synthesis modes electrostatic and non-electrostatic assembly... 

Because the way in which a mesostructure is prepared affects the structure, morphology and surface chemistry of the product obtained, the mesostructure formation mechanism is also expected to impact the preparation of functionalized derivatives. Mesostructure synthesis pathways can be subdivided into two general categories electrostatic and non-electrostatic pathways. 

Fig. 2. R-Si(OR )3 molecules employed in mesostructure synthesis a) phenyltrimethoxysilane (PTMOS), b) vinyl-trimethoxysllane (VTMOS), c) octyltrimethoxysilane (OTMOS).

Shengyuan, Y, et al.. Rice grain-shaped TiO mesostructures—synthesis, characterization and applications in dye-sensitized solar cells and photocatalysis. Journal of Materials Chemistry, 2011,21(18), 6541-6548. 

Monnier, A Schuth, F Huo, Q Kumar, D Margolese, D Maxwell, RS Smcky, GD Krish-namurty, M Petroff, P Firouzi, A Janicke, M ChmeUca, BE, Cooperative Formation of Inorganic-Organic Interfaces in the Synthesis of Silicate Mesostructures, Science 261, 1299, 1993. 

Fowler, C.E., Khushlani, D. and Mann, S. (2001) Interfacial synthesis of hollow microspheres of mesostructured silica. Chemical Communications, 2028-2029. 

XRD patterns and data from table 1 confirm the ordered 2D (P6mm) mesostructure of SBA-15 and Al-SBA-15 whatever the synthesis method. 

Ordered mesoporous materials of compositions other than silica or silica-alumina are also accessible. Employing the micelle templating route, several oxidic mesostructures have been made. Unfortunately, the pores of many such materials collapse upon template removal by calcination. The oxides in the pore walls are often not very well condensed or suffer from reciystallization of the oxides. In some cases, even changes of the oxidation state of the metals may play a role. Stabilization of the pore walls in post-synthesis results in a material that is rather stable toward calcination. By post-synthetic treatment with phosphoric acid, stable alumina, titania, and zirconia mesophases were obtained (see [27] and references therein). The phosphoric acid results in further condensation of the pore walls and the materials can be calcined with preservation of the pore system. Not only mesoporous oxidic materials but also phosphates, sulfides, and selenides can be obtained by surfactant templating. These materials have pore systems similar to OMS materials. 

For some reviews, see (a) Majoral J-P (2007) Influence of cationic phosphorus dendrimers on the surfactant-induced synthesis of mesostructured nanoporous silica. New J Chem 31 1259-1263 (b) Puntoriero F, Nastasi F, Cavazzini M et al (2007) Coupling synthetic antenna and electron donor species a tetranuclear mixed-metal Os(II)-Ru(II) dendrimer containing six phenothiazine donor subunits at the periphery. Coord Chem Rev... 

The influence of the nature of the aluminum source on the acidic properties of mesostructured materials (MCM41) has also been studied in the literature [244]. Microcalorimetry experiments using ammonia as a probe molecule have shown that Al insertion into the mesoporous silicate framework affected acid site strength and distribution in a manner controlled by the synthesis conditions (materials prepared... 

Suzuki K, Ikari K, Imai H (2004) Synthesis of silica nanoparticles having a well-ordered mesostructure using a double surfactant system. J Am Chem Soc 126 462-463... 

To improve the meso-structural order and stability of the mesoporous silica ropes, a postsynthesis ammonia hydrothermal treatment (at 100 °C) was invoked. As indicated by the XRD profile in Fig. 3A, 4-5, sharp features are readily observed in ammonia hydrothermal treated samples. Moreover, after the post-synthesis ammonia treatment, the sample also possesses a sharp capillary condensation at p/po 0.35(Fig. 3B) corresponding to a much narrower BJH pore size distribution of ca. 0.12 nm (at FWHM). In other words, the mesostructures are not only more uniform but also more stable when subjected to the post-synthesis treatment. The morphology of the silica ropes remained unchanged during the ammonia hydrothermal process. The mesostructures remain intact under hydrothermal at 100 °C in water even for extended reaction time (> 12 h). 

When the temperature is increased to 100 °C, the formation period of regular hexagonal mesostructure can be shortened dramatically to about 3 5 days. Between 100-150 °C, the XRD patterns of the obtained solids clearly show all four diffraction peaks. However, when the temperature is increased to around 160 °C, the resulting solid shows only one [100] diffraction peak which is typical of disordered mesoporous phases. When the temperature is further elevated to 185 °C, only amorphous phase is produced, regardless of the period of the synthesis. 

MCM-41 samples with increased hydrothermal stability could be successfully synthesized by adding additional salts like tetraalkylammonium bromide or sodium bromide to the synthesis gel. The increased stability is related to the increased condensation of the silanol groups during the formation of the mesostructure. Hydrothermally stable MCM-41 structures with different pore diameter can also be synthesized by this method using surfactants with varied chain length. 

First Synthesis of Mesostructured Hexagonal Germanium Sulfides Using Gemini Surfactants... 

Since the first synthesis of mesoporous M41S alumosilicates in 1992 [1,2] numerous systems of mesoporous materials have been reported. The principle method of these syntheses consists of the utilisation of lyotropic liquid crystals as supramolecular templates, which act as structure directing agents in order to mesostructure inorganic building units. 

Synthesis and characterization of mesostructured molybdenum sulfides with intercalated cationic surfactants... 

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. 

Synthesis and characterization of novel mesostructured tungsten sulfides Charles (Chibiao) Liu and, Amy Ferryman, Julia E. Fulghum, Songping D. Huang Department of Chemistry, Kent State University, Kent, OH 44242, USA Dedicated to Dr. Richard H. Fish on the occasion of his 60th birthday... 

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