Martin-Luther-Universität Halle-Wittenberg

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Herr Prof. Dr. T. Hahn

Telefon: 0345 55-25910
Telefon: 0345 55-25903
Telefax: 0345 55-27163

Von-Danckelmann-Platz 4
06120 Halle

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AK Prof. Hahn

Research Interests

Controlled Pore Glasses (CPG)

Controlled Pore Glasses (CPG) are prepared from alkali borosilicate glasses by phase separation and combined acid and alkaline leaching treatments. As a result of the temperature-depending phase separation of alkali borosilicate glasses two different phases are obtained. The first one is almost pure silica. The other one is an alkali-rich borate phase with different amounts of silica dissolved in it. Because of the small solubility of silica in acids it remains after the extraction as finely dispersed silica in the cavities of the main silica framework and affects the pore structure of microporous glasses. The treatment with alkaline solution removes the finely dispersed silica, macroporous glasses are obtained. The resulting porous glasses have pores of 0.3 to 1000 nm in diameter, which depends on the glass composition and phase-separation temperature. They are generally characterized by large specific surface areas. Porous glasses show, in comparison with other porous inorganic solids, a high thermal stability and resistance to acids. They can be preapared in various geometric forms, i.e., as beads, rods and plates. Controlled Pore Glasses are used as carrier for catalysts or for functional materials, as packing material for HPLC, as host material in non linear optic devices and as macromolecular sieves in biochemistry. Small quantities of alumina increase the surface acidity of silica. Al-modification of micro/mesoporous glasses leads to the formation of strong Brönsted-acid sites by tetrahedral coordination of aluminium in the silica-framework. The resulting porous glasses show catalytic activity for cumene cracking. One of research fields deals with the preparation, structural characterization and application of spherical mesoporous molecular sieves with pore sizes between < 2 and 5 nm on the basis of colloidal silica inside the original pores of a macroporous Controlled Pore Glass. Possible applications of the mesoporous glass beads can be as catalyst for reactions of bulky organic compounds, as catalyst support or as packing material for HPLC.

Futhermore, ultrathin porous glass plates

Futhermore, ultrathin porous glass plates

Futhermore, ultrathin porous glass plates (20 x 15 x 0,1 - 0,5 mm) with pores between < 2 and 150 nm were developed. These materials can be used as membranes for gas seperation, as catalytic active membranes or for host-guest investigations.

texture and surface characterization of amorphous porous silicates

texture and surface characterization of amorphous porous silicates

Another field of research is the structure, texture and surface characterization of amorphous porous silicates (xerogels, porous glasses, sol-gel materials, MCM-41). Therefore for these materials we presently develop a complex procedure to estimate the structure and texture parameters by combined examination of the results of various investigation methods (adsorption measurements, mercury intrusion, electron microscopie, SAXS, WAXS, shape selective catalysis). As a result for the investigated porous silicate it should be possible to generate a detailed model of the microstructure (pore size, pore length, pores per gramm). These parameters become more and more important for the application of porous silicates as host material, in membrane science and a deeper understanding of heterogeneous catalyzed reactions.

Heterogeneous Catalysis

The studies in the field of heterogeneous catalysis deal with the application of the olefin hydrogenation over nickel catalyst supported on xerogels, Controlled Pore Glasses (CPG), sol-gel and MCM materials as shape selective test reaction for the structure characterization of mesoporous silicates.

Host-Guest Chemistry

The study of liquid crystalline systems confined to a random network is a very rich area of research. Fundamental questions of how phase structure and transition are modified by a confining environment remain open issues. Complex liquid crystals confined in randomly interconnected porous networks are unique systems in that they allow us to address such questions. Our group is fortunately able to use the defined pore network of porous glasses (pores < 2 to 100 nm) and to prepare a specific form (ultrathin plates) of this material for application in the field of host-guest investigations. Different effects depending on wether the host material length scale is larger or smaller than the thermal correlation length of the liquid crystal confined to the pore network are investigated. High resolution calorimetry, dielectric relaxation measurements and nonlinear absorption measurements (second harmonic generation) are probing the orientational order and the thermodynamic of the phase behavior of the liquid crystals confined to the porous glass network.

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