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Sensing, Separations and Artificial Photosynthetic Assemblies Based on the Architechture of Zeolite Y and Zeolite L

by White, Jeremy Clayton

Abstract (Summary)
The growth of zeolite L membranes with controlled thicknesses in the sub-micron to micron region is examined. It was demonstrated that by controlling the concentration of the zeolite solid load and suspension viscosity, dip-coating provided a method to prepare zeolite seed layers of controlled thicknesses. Disk-shaped zeolite L crystals, with size distribution of 0.5-2 microns in diameter, were used as seed crystals for the growth of 2-7 micron thick membranes. For the synthesis of sub-micron sized membranes, seed crystals from 20-60 nanometers were used. The optimum secondary growth conditions was found to occur at 60 hours of growth time (40 hours for sub-micron membranes) using a temperature of 110ºC with a solution composition of 10K2O:1Al2O3:20SiO2:2000H2O. Membranes were characterized by electron microscopy and single gas permeation studies, providing confirmation of membrane densification. Composite, defect-free membranes consisting of zeolite Y layers on the surface of microporous ?-Al2O3 support disks were prepared using externally synthesized nanocrystalline and sub-micron crystals. Polycrystalline layers were formed by two different hydrothermal secondary growth procedures. Nanocrystalline zeolite Y seeded membranes were utilized as chemical sensors for the detection of chemical warfare agents. Sensor traces were established to show that despite the good membrane sensitivity to DMMP, sensor recovery times were too long for practical applications. Due to the ability of small molecules to pass one another inside the micropores of zeolites, two different zeolite Y membrane types were prepared from sub-micron crystallites to investigate their gas transport and separation properties. Single gas permeances for helium were determined in the temperature range of 30-130ºC for both membrane types. The separation factors of equimolar mixtures of CO2 and N2 were measured at the same temperatures and at feed pressures from 1.4-4 bar. Both membrane types showed high separation factors between CO2 and N2 due to selective adsorption of CO2 in the sub-nanometer micropores of the membrane. For practical applications, it was determined that a slower, more controlled growth leads to membranes that have good interparticle connectivity, thus leading to higher permeances and excellent CO2/N2 separation properties. Motivated by the light and chemical processes that take place in photosynthesis, the objective of this research was to develop integrated photochemical molecular assemblies for the conversion of solar to chemical energy. In order to exploit the charge separation, the microstructure of zeolite Y has been utilized to develop hybridized photocatalysts using a variety of combinations of CdS, TiO2, and Pt. Novel procedures have been developed for synthesizing nanoparticles of these three materials within the microstructure of zeolite Y. Single, binary, and ternary systems were studied for hydrogen production from water containing Na2S and Na2SO3 as a sacrificial reagents under ultraviolet/visible light irradiation. The order in which these materials were integrated into the zeolite was optimized to provide the highest hydrogen production efficiency. The significant improvements in hydrogen production can be attributed to the ability of zeolite Y to organize these materials in a manner that provides good particle junctions, thus improved catalytic properties.
Bibliographical Information:

Advisor:

School:The Ohio State University

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:zeolite membrane artificial photosynthesis gas separation sensor cadmium sulfide

ISBN:

Date of Publication:06/26/2009

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