9 Self-assembly of organic-inorganic structures

9 Self-assembly of organic-inorganic structures - Lecture 9...

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MSE 316 Feb 5, 2009 Self-assembly of organic-inorganic mesostructures Topics • Zeolites • Co-assembly of mesostructures (MCM-41) • Characterization techniques - small angle x-ray diffraction - wide angle x-ray diffraction Lecture 9
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Zeolites Philip Ball, Made to Measure , p. 284. Natural zeolites are aluminosilicate minerals whose crystal structure is composed of tetrahedral units, in which either silicon or aluminum atoms are surrounded by four oxygens. These units are linked together into rings that form an open network of cavities connected by pores. Zeolites are frequently called molecular sieves because they can be used to sort molecules by size. Every atom is on the surface. Zeolites are widely used as catalysts.
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Templating synthetic zeolites In the 1960’s George Kerr and colleagues at Mobil discovered that organic ions could be used to direct the growth of zeolites with new types of pore structures. They used tetraalklyammonium ions. Philip Ball, Made to Measure , p. 287.
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Synthetic molecular sieves This synthetic gallophosphate molecular sieve cloverite was first made in 1990. Its pores have 13.2 Å openings. Philip Ball, Made to Measure , p. 289.
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Mesoporous materials C. Sanchez et al. Chem. Rev. 102 (2002) p. 4093. The zeolites and synthetic molecular sieves are known as microporous materials. They have pore diameters less than 1.5 nm. Macroporous materials are made by techniques such as grinding materials up into fine powders. The pore diameter is not homogenous unless something special is done. The pore size is generally greater than 30 nm. Mesoporous materials have pore sizes between 2 and 50 nm. It took chemists many years to figure out how to make them.
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Additional comments on the previous slide Pore size distribution Note that all of the pores in the zeolites have the same size. The gels and porous glasses, however, have a broad distibution of sizes. Having a tight
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9 Self-assembly of organic-inorganic structures - Lecture 9...

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