Graduate Program

Chemistry

Degree Name

Master of Science (MS)

Semester of Degree Completion

2007

Thesis Director

Jonathan Blitz

Thesis Committee Member

Doug Klarup

Thesis Committee Member

Daniel Sheeran

Thesis Committee Member

Scott Tremain

Abstract

A variety of oxides such as silica, alumina, titania and mixed oxides such as silica/alumina (SA), silica/titania (ST) and alumina/silica/titania (AST) are investigated by TGA and FTIR. These mixed oxides are analyzed because of their applications as catalysts. Thermogravimetric analysis is done on all the samples to determine the temperature at which the weakly adsorbed water is lost and the surface is left with only surface hydroxyls. TGA data showed the loss of most of the adsorbed water at around 100°C.

From the diffuse reflectance FTIR spectra taken at 200 and 300°C the silanol content is estimated from the 3740 cm band intensity. Silanol content is estimated for SA and ST samples in order to determine the loss of silanol content with increase in titania or alumina phase. The decrease in silanol content with an increase in alumina and titania contents is observed, though the trend is not smooth at low alumina and titania contents. Among ST samples ST 20 did not show much loss in silanol content.

ST samples are extensively studied as these represent a novel class of catalyst. Catalytic active sites are generated on the surface of ST samples as a result of formation of Si-O-Ti bonds. Quantitative characterization of Si-O-Ti linkages by FTIR transmission spectroscopy shows maximum Si-O-Ti bond formation for ST 20 (80% of silica and 20% of titania). The formation of a maximum number of Si-O-Ti bonds for ST 20 is an indication of greater degree of dispersion of titania in the silica matrix.

Adsorption studies are done on the silica surface modified with various organofunctional silanes for the purpose of enhancing adsorption for photocatalytic decomposition on silica-titanias. Methylene blue is chosen as a dye for studying the adsorption behaviour of silica and various modified silicas. Adsorption isotherms of thiocyano and thiol groups modified on silica showed a greater adsorption for methylene blue and hence these groups were chosen for surface modification on to ST samples.

Since ST 20 did not exhibit significant loss in silanol content while retaining considerable titania content, this material was chosen for photocatalytic experiments. The relatively large silanol content provides the capability for significant surface functionalization to control adsorption properties, while retaining the photocatalytic titania active sites.

After modification of ST 20 with thiol and thiocyano groups, adsorption and photocatalytic decomposition behavior of methylene blue with ST 20, thiol modified ST 20 and thiocyano modified ST 20 were studied. From these studies, photocatalytic activity of SCN modified ST 20 is found to be greater than that of ST 20.

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