Andrew Ichimura of San Francisco State University is supported by the Experimental Physical Chemistry Program to carry out an integrated materials chemistry research and education project. The central research hypothesis is that pure silica zeolite films doped with alkali metals will become semi-metals or conductors depending on the size and connectivity of the zeolite pores, the specific metal, and its concentration. Alkali metal doped pure silica zeolite (M@Z; M= Na-Cs) films will be prepared from zeolites with different channel sizes and structures (for example,1D or 3D). It will be demonstrated that high quality multilayered structures can be prepared that will enable new studies of charge transport within and through a zeolite film. Various spectroscopic methods and conductivity measurements will be used to establish the structure and properties of the material and interfacial regions. Outcomes are expected to demonstrate the directional charge transport according to the channel orientation with respect to applied current. A major goal is to determine whether conduction is activated or intrinsic to particular M@SZ materials. Fundamental studies of nanoporous zeolite films will expand the scope and applications of silica zeolites, advance the understanding of chemical and physical phenomena and inorganic-organic interfaces, and permit studies of low-dimensional conductivity in nanoporous solids. The educational component will incorporate materials chemistry into the curriculum at SFSU, a primarily undergraduate institution, and enable unique research opportunities for undergraduate and master's level students.

Outcomes of this research are expected to impact solid-state chemistry at zeolites, zeolite films, and self-assembled monolayers, possibly opening new avenues of research and applications. Anticipated understandings of zeolite film growth may advance the use of nanoporous films as sensors and electrodes, and provide routes to prepare other technologically important oxide films. New physical chemistry laboratory experiments to be developed and implemented will revitalize the chemistry curriculum in the direction of nanoscale research, an important and innovative area of current chemical interest.

Project Report

Intellectual Merit The NSF CAREER award advanced research and student training in materials related to energy and the environment at San Francisco State University. New and better methods for preparing thin films (< 1 μm) of zeolites (SiO2), titano-silicate zeolties ((Ti)SiO2) and semiconductors such as titanium dioxide (TiO2), pyrite (FeS2), and molybdenum disulfide (MoS2) were developed. Research during the award period focused on the synthesis and characterization of zeolite and semiconductor thin films. Preliminary experiments were conducted to explore suitable applications. Zeolite Thin Films. Zeolites are essential catalysts in the petroleum industry and thin films or membranes find use in separations, size-selective electrodes, and even detectors. In this work, we characterized cesium-doped MFI films and found them to be insulators despite theoretical predictions. We also developed new methods to prepare titanium-doped silica zeolite films, which are excellent selective oxidative photocatalysts and also convert CO2 under UV light to fuels such as methanol and methane. The goal of this work is to prepare continuous thin films of Ti-BEA and Ti-MFI with varying amounts of titanium. We have succeeded in this goal preparing Ti-BEA films for the first time. Our goal is to explore the photo-reduction of CO2 with water and UV light and to improve on the photocatalytic efficiency of these materials. Semiconductor Thin Films. The anatase phase of TiO2 is of interest because it is nontoxic, made from abundant elements, and is an excellent photocatalyst. In recent work, we have shown that oriented anatase TiO2 thin films can be prepared that have ~100% {001} facets at the surface of the film (Figure 1). This reactive surface is useful for generating H2 gas from H2O (water splitting) and creating reactive oxygen species (ROS) such as hydroxyl radicals in aqueous solutions under UV illumination. For example, our TiO2 films are superior to high surface area powders for water splitting and H2 generation when the film is sparsely populated with platinum nanoparticles. Our films in generate up to 20x more H2 than comparable platinum loaded anatase powders reported in the literature. In addition, our thin TiO2 films are superior to P25 (standard TiO2 material) by a factor of 10 for water decontamination when normalized to the surface area of each material. The two metal sulfides, FeS2 and MoS2, that can be activated with sunlight have applications in solar cells and H2 production, respectively, Figure 2. The pyrite phase of FeS2 has a large absorption coefficient in the visible region of the spectrum and thus could be used to prepare thin absorbing layers for photovoltaic cells. The layered MoS2 structure is a known desulfurization catalyst but is also effective at splitting water using visible light. We are optimizing methods to produce thin films of FeS2 and MoS2 and then will investigate their use in solar cells and H2 evolution, respectively. Broader Impacts The PI has trained 15 undergraduate, 8 graduate, and 6 high school students throughout the period of the award. Approximately half of the students were women and 7 students belonged to underrepresented groups (e.g., African-American, Latino, Native American). Two students earned their M.S. Chemistry degrees during the award period (S. Usmani, 2010; G. Angha, 2012) and 6 are continuing. Students presented their work at national meetings such as the Materials Research Society meeting, American Association of Crystal Growth, and Gordon Conference on Microporous Materials. In total, 24 posters were presented undergraduate and graduate students at national conferences since 2008. The PI has contributed to a Materials Chemistry focus area at SFSU through the development of a graduate course in electron microscopy and laboratory experiments for the undergraduate physical chemistry laboratory (e.g., Preparation of CdS Quantum Dots, X-ray Diffraction of Salts, Surface Tension). Three papers have been published and eight manuscripts are in preparation.

Agency
National Science Foundation (NSF)
Institute
Division of Chemistry (CHE)
Application #
0645814
Program Officer
Charles D. Pibel
Project Start
Project End
Budget Start
2007-03-01
Budget End
2013-02-28
Support Year
Fiscal Year
2006
Total Cost
$589,458
Indirect Cost
Name
San Francisco State University
Department
Type
DUNS #
City
San Francisco
State
CA
Country
United States
Zip Code
94132