Chemically tailored new sorbents for use into the 21st century.

Bambrough, Claire Michelle (1998). Chemically tailored new sorbents for use into the 21st century. PhD thesis The Open University.



A series of chemically-tailored mesoporous materials has been synthesized via a liquid-crystal templating mechanism and characterized using a variety of techniques. Materials include a series of MCM-41-type solids (including aluminosilicates, purely siliceous, and iron-containing materials) and a series of organically-modified mesoporous silicas (including phenyl-, vinyl-, aminopropyl- and mercaptopropyl-functionalized samples).

Two different synthesis compositions and three different sets of reaction conditions were tested for the synthesis of MCM-41. Characterization by XRD and N2 sorption demonstrated that synthesis under pressure at 100 °C yielded materials with a uniform pore structure and narrow pore size distribution. Samples with pore widths in the mesoporous range and specific surface areas of between 500 - 950 m2 g-1 were produced. The synthesis composition that used aluminium sulphate as the aluminium source was shown, by 27A1 MAS-NMR, to give a product, following calcination, containing tetrahedrally co-ordinated aluminium (necessary for acid catalysis).

N2 adsorption on the organically-modified, samples, demonstrated that the incorporation of organic functions reduced the pore diameter and yielded microporous materials. The use of auxiliary organics as pore-swelling agents was investigated and mesitylene was proved to be successful in the formation of a mesoporous phenyl-modified material.

The adsorption isotherms of water, benzene, n-butanol and t-butanol were measured for the phenyl-modified materials. N2, benzene and t-butanol sorption on the unswollen sample yielded Type I isotherms, confirming the sample’s microporosity. Type IV isotherms were given by these adsorptives on the mesitylene-swollen sample, demonstrating the presence of mesopores.

n-butanol adsorption occurred via polar interactions with the surface hydroxyl groups of both samples and was sterically-hindered in the microporous sample. Water sorption (performed on the unswollen sample. only) gave a Type V isotherm demonstrating the sample’s hydrophobicity.

IINS studies of the phenyl-modified silica containing adsorbed benzene, detected the presence of the adsorbed species and differentiated between structural phenyls and adsorbed benzene.

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