Non-thermal calcination by ultraviolet irradiation in the synthesis of microporous materials

Abstract

We describe a new photochemical method near room temperature conditions for the removal of organic structure-directing agents in the synthesis of microporous materials. The method relies on the exposure of the sample to short-wavelength ultraviolet (UV) radiation in air and the ozone environment generated by a medium pressure mercury lamp (184–257 nm). The generality of the approach has been confirmed using three test-cases of microporous materials: a high-silica synthetic zeolite, an aluminophosphate, and a Ge-substituted microporous silica. The structures and organic contents of the microporous materials before and after UV/ozone treatment were determined using a combination of X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetry, and nitrogen adsorption isotherms. For all three cases, the UV/Ozone treatment allows complete removal of the organic template while retaining the inorganic framework. The overall integrity of the microporous materials was comparable to or better than for materials derived by thermal calcination. This method is applicable in making new materials from organic–inorganic precursors and holds promise for microporous thin films on thermally sensitive substrates and for controlled spatial patterning.