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Mariam N. Ismail, Julo Warzywoda, Kate Ziemer, and Al Sacco, Jr. Deep space missions will become increasingly more important this century. These missions require strict control over commodities such as water, food, and energy. The use of multifunctional materials must be maximized in order to provide the greatest flexibility to the astronauts of the future. Zeotype thin films and membranes gain much of their functionality from the unique crystalline and porous structure of the zeotype material. They also have the additional benefit of high thermal and chemical stability. Titanosilicate ETS-10 zeotype material (Figure 1) containing titanium in its framework structure is photocatalytically active. Photocatalysis can be used to purify air and water both in space and terrestrially.
Figure 1: Titanosilicate ETS-10 framework structure Typical photocatalysis is initiated when light of a specific wavelength is absorbed by the photocatalyst. Light sources traditionally used in photocatalysis emit a spectrum of wavelengths; however, only one wavelength, with energy equal to or greater than the photocatalyst material band gap energy, is sufficient to initiate the photocatalytic reaction. The most energy-efficient photocatalysis system would utilize light with a narrow-range of wavelengths. This narrow range of wavelengths can be produced by a class of semiconductors, called optoelectronic materials, which create light.
Figure 2: Scanning electron microscope image of ETS-10 crystals attached onto glass substrate modified using photoconductive linker. Current research is focused on preparation of a thin film of titanosilicate ETS-10 photocatalyst on an optoelectronic semiconductor substrate - Gallium Nitride (GaN). The substrate would be able to produce narrow-range wavelength light and that light would be used by the thin film to perform photocatalysis. But, in order for the photocatalytic reaction to be initiated, modification of the materials will be necessary. Two approaches can be considered - modification of GaN, or modification of ETS-10. Due to availability of resources, modification of ETS-10 will be pursued by means of post acid treatments or the incorporation of transition metals such as V in the structure of ETS-10, which results in lowering the band gap energy. Several film growth methods are currently being investigated, such as in situ hydrothermal film growth, secondary film growth, and the use of photoconductive linkers. In the case of film growth via photoconductive linkers, the substrate surface will be modified using these linkers (Figure 2). Once this modification is successful, an attempt at attaching the ETS-10 crystals will be pursued. |
