Mesoporous metal oxides, precursors

In summary, highly cubic ordered cobalt oxides with crystalline walls have been synthesized by an accurately controlled incipient wetness approach using mesoporous silica as hard template and cobalt nitrate as the precursors. Compared with the previously reported solution impregnation processes, this technique is facile, time-saving and economical. This technique can be used to synthesize ordered mesoporous metal oxides, and we expect that rvith this approach various kinds of mesoporous oxides or other materials can be synthesized, which may benefits their applications in many areas such as in catalysis, sensors, clean energy and electronics. 

In general, metal chlorides or metal alkoxides were used as metal oxide precursors that, when contacted with alcoholic solutions of a variety of block copolymers, formed mesostructured solids. To limit the rates of hydrolysis and condensation, the above mixtures were simply allowed to stand in air for variable times (1—30 days), whereby moisture was absorbed, thus providing a "controlled" source of water. High surface area (100— 800 m /g), thermally robust, mesoporous (3-12 nm pore diameter maxima) samples of pure and mixed metal... 

Wong, M.S. Jeng, E.S. Ying. J.Y. Supramolecular templating of thermally stable crystalline mesoporous metal oxides using nanoparticulate precursors. Nano Lett. 2001. 1. 637. 

Xu C, Xu G, Liu Y, Zhao X, Guanghou WG (2002) Preparation and characterization of SnO nanorods by thermal decomposition of SnC O precursor. Seri Mater 46 789-794 Yang HX, Qian JF, Chen ZX, Ai XP, Cao YL (2007) Multilayered nanocrystaUine SnO hollow microspheres S3mthe-sized by chemically induced self-assembly in the hydrothermal environment. J Phys Chem 111 14067-14071 Yuan L, Hyodo T, Shimizu Y, Egashira M (2011) Preparation of mesoporous and/or macroporous SnO -based powders and their gas-sensing properties as thick film sensors. Sensors 11 (2) 1261-1276 Yue W, Zhou W (2008) Crystalline mesoporous metal oxide. Progr Nat Sci 18 1329-1338... 

In this strategy, the mild experimental conditions required for the synthesis of PCP allow the coexistence of the PCP precursors with the same supramolecular assemblies of surfactant molecules that are traditionally used for the synthesis of mesoporous metal oxide materials. The rational adjustment of the interactions between PCP precimsors and surfactant molecules as well as the kinetics of sirnfactant assembly and PCP crystallization results in the cooperative assembly of smTactants and PCP growth units. Macro- or mesoporous PCP-based materials are recovered after the removal of the templates (see Mesoporous Metal-Organic Frameworks). 

Non-aqueous synthetic methods have recently been used to assemble mesoporous transition metal oxides and sulfides. This approach may afford greater control over the condensation-polymerization chemistry of precursor species and lead to enhanced surface area materials and well ordered structures [38, 39], For the first time, a rational synthesis of mesostructured metal germanium sulfides from the co-assembly of adamantanoid [Ge4S ()]4 cluster precursors was reported [38], Formamide was used as a solvent to co-assemble surfactant and adamantanoid clusters, while M2+/1+ transition metal ions were used to link the clusters (see Fig. 2.2). This produced exceptionally well-ordered mesostructured metal germanium sulfide materials, which could find application in detoxification of heavy metals, sensing of sulfurous vapors and the formation of semiconductor quantum anti-dot devices. 

Although hydrotalcites are relahvely stable (up to circa 500 °C), they are also of potential applicahon as precursors of mixed metal oxide catalysts, for example Reference [66]. Dehydrahon-rehydration equilibria account for the switching between hydrotalcites and mixed/supported metal oxides, which is somehmes termed the memory effect [67-69]. Recent advances have seen attempts to prepare highly dispersed LDH systems, such as those dispersed within mesoporous carbon [70]. Owing to widespread interest in their application, hydrotalcite catalysts have been the subject of a number of reviews, for example References [71-75]. Other layered-based systems have also attracted attention for application in catalysis, for example Reference [76]. 

Well ordered mesoporous silicate films were prepared in supercritical carbon dioxide.[218] In the synthesis in aqueous or alcoholic solution, film morphology of preorganized surfactants on substrate cannot be fully prescribed before silica-framework formation, because structure evolution is coincident with precursor condensation. The rapid and efficient preparation of mesostructured metal oxides by the in situ condensation of metal oxides within preformed nonionic surfactants can be done in supercritical CCU- The synthesis procedure is as follows. A copolymer template is prepared by spin-coating from a solution containing a suitable acid catalyst. Upon drying and annealing to induce microphase separation and enhance order, the acid partitions into the hydrophilic domain of the template. The template is then exposed to a solution of metal alkoxide in humidified supercritical C02. The precursor diffuses into the template and condenses selectively within the acidic hydrophilic domain of the copolymer to form the incipient metal oxide network. The templates did not go into the C02 phase because their solubility is very low. The alcohol by-product of alkoxide condensation is extracted rapidly from the film into the C02 phase, which promotes rapid and extensive network condensation. Because the template and the metal oxide network form in discrete steps, it is possible to pattern the template via lithography or to orient the copolymer domains before the formation of the metal oxide network. 

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