Entrapment of Probe Species

Of major concern is the potential for leaching of the probe from the sol-gel matrix during the processing steps required to prepare the aerogel from the wet sol-gel. As was noted by Pierre and Pajonk [7] and Leventis et al. [11], among others, the multiple 

Nevertheless, Morris et al. [14] demonstrated that molecular species, such as acid-base indicators, can be trapped noncovalently within sihca composite aerogels prepared using CSCE extraction methods. (This work is described in more detail in Sect. 27.2.6.) 

One way to overcome the issue of leaching is to entrap species that are so physically large that it is difficult or impossible for them to leach from the matrix. Wallace et al. [15] were able to entrap within silica aerogels protein superstructures of cytochrome c cyt c) around gold nanoparticles. They demonstrated the apphcabihty of these materials for gas-phase NO sensing. The size of the cyt c superstructures is such that the resulting material can be considered a composite consequently, this work is described in more detail in Sect. 27.2.6. 

Recently, we have compared probe-doped RSCE aerogels, CSCE aerogels and xerogels, aU prepared from the same precursor mixmres [17]. The oxygen-sensitive probes PtOEP and platinum (II) mesotetrafluoro phenylporphyrin (PtTFPP) were included in the TMOS precursor mixture, and then aliquots of the mixmre were processed in three different ways. 

Silica Aerogels as Sample Holders for Raman Scattering Measurements 

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