Gold-Containing Chitosan-Silica Aerogels

Chemistry of Gold-Containing Chitosan-Silica Aerogels 

The condition, if all else is constant , suggests the question what if other entities are present This is especially important in the field of nanochemistry/nanotechnology, where metal-containing nanoparticles usually are covered with small molecules to prevent them from agglomerating instead of staying separate. Typically, a surfactant is applied to cover the nanoparticles as they are being formed. 

In the case of SiO2-X-Au(0) aerogels, however, no surface-coating molecules are used to keep the Au(0) particles apart the aerogel structure and the growth mechanism play that role. The experimental question then becomes what happens if molecules that interact with Au(0) are present as they are grown photolytically in the aerogels  

Liu addressed this question using biologically relevant molecules and model compounds that can interact with Au(0) surfaces cystamine, cysteamine, biotinylated thiol-6 and biotinylated disulfide-5, as well as the thiols 11-mercapto-l-undecanol and 11-mercapto undecanoic acid [26]. In each case, the molecule was added to a dry Si02-X-Au(III) aerogel before photolysis. 

It is clear that these molecules limit the growth of Au(0) particles. The interpretation presented by X. Liu and coworkers [26, 27] is that the Au(0) particles grow to the size at which the attaching molecules have effectively covered the surface. Once that is 

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Figure 18.14. Average sizes of gold nanoparticles formed by UV photolysis of gold-chitosan-silica [13] aerogels containing 10% chitosan and the indicated ratio of Au(III) (as AuCU ) to amine. The squares denote those aerogels, the others denote them with the indicated molecule present during the photolysis.

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