Engelhard titanosilicate ETS-10 is a large-pore zeotype material [1] with well-defined monatomic semiconductor …Ti-O-Ti-O-Ti… chains (Eg = 4.03 eV), which make this material a promising candidate in photocatalytic applications [2]. Light sources typically used in photocatalysis emit a spectrum of wavelengths; however, only wavelengths with energy equal to or greater than the material's band gap energy are sufficient to initiate the photocatalytic reaction. One strategy to improve the efficiency of photocatalytic devices is to use a photon source, such as optoelectronic semiconductor materials that produce a high density of photons in a narrow range determined by the material's band gap, while minimizing the productions of unusable photons whose energy is below the band gap of the catalytic material. Gallium nitride (GaN) is one of the most promising optoelectronic semiconductors for such applications as blue/UV light emitting diodes (LEDs) due to its direct transition band structure (3.39 eV [3]) and the ability to tune its bandgap energy up to 6.2 eV (AlN) [4] through the incorporation of Al. Thus, immobilization of ETS-10 crystals onto GaN will allow the direct use of the light emitted from the LED in activating the crystals for photocatalytic reactions when sun light is not available.

Molecular linkers, such as organosilanes, have been used to functionalize glass substrates for covalent attachment of ZSM-5 and zeolite A crystals [5, 6]. The use of these linkers has also been reported for functionalization of GaN in applications such as immobilization of biomolecules [7-9]. However, functionalization of GaN in zeolite-type applications has not been reported to date.

Here, the functionalization of n-type GaN (0002) substrates using aminopropyl trimethoxysilane (APTMS), and the attachment of ETS-10 crystals on the functionalized substrates are reported. Successful functionalization was confirmed through X-ray photoelectron spectroscopy (XPS) observation of the Si 2p core-level emission, since this element is only present in the linker material. Assembly of ETS-10 crystals on the APTMS functionalized GaN substrates via dip coating resulted in a firm attachment as determined by means of successive sonication for up to 30 min. These results suggest a strong covalent attachment between the surface hydroxyl groups of the zeolite and the APTMS linker from the functionalized substrates. Testing is presently underway to determine the effect of the linkers on photon transmission.

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