Molecular sieve-based host/guest compounds: Materials for optical gas sensing

摘要

The presence of different gas atmospheres is optically detected by the use of molecular sieves modified with metal oxide clusters or dye molecules. The reversible redox behavior of intrazeolitic titanium and tin dioxide clusters in reducing and oxidizing atmospheres (H_2, CO, O_2) is studied by in-situ diffuse reflectance UV/Vis spectroscopy. The nuclearity of the different clusters stabilized in the pores of molecular sieve NaY can be deduced from the blue-shifts of absorption edges in diffuse reflectance UV/Vis spectra and from the behavior towards reduction. The response time of hosted mononuclear Ti~(IV)O_x species for the registration of H_2 is shortened by a factor of about 10 in comparison to 4 nm TiO_2 particles. Concentrations down to 50 ppm CO in air can be optically detected by SnO_2 clusters in NaY. SO_2 can be deduced from the quenching of the fluorescence of rhodamine dye molecules anchored in the pores of Si-MCM-41.