Precursor molecules, silicates

Precursor Molecules identifies common silicate precursors and their synthesis. 

In a reverse microemulsion, the hydrolysis and polymerization of the silicate precursor occur in the water droplet, therefore, to dope dyes in the silica nanoparticles they must be water soluble. However, a number of organic dye molecules are hydrophobic, requiring modifications prior to doping. Several methods are available to link a hydrophobic dye molecule to a water soluble group. A simple and effective example is to link a hydrophilic dextran to the dye molecules [8]. This modification can greatly enhance the water solubility of hydrophobic dye molecules, but will increase the cost of resultant DDSNs. 

The synthesis of MCM-41 structure in fluoride medium has been reported by Silva and Pastore [10], who used sodium silicate as silica source and carried out crystallization at 150 °C. They suggested the behaviour of Si02-CTMA+-F system was significantly different from that reported previously on the mesophase system. It is known that fluoride ions do influence the nature, activity and polymerizing capacity of silica precursors, and a fluorinated silica surface is much more hydrophobic and more resistant to the attack of water molecules than a silanol silica surface [11]. 

As a totally different post-synthesis method that is firmly based on the structural charaderistics of MWW, reversible strudural conversion between 3D MWW silicate and its corresponding 2D lamellar precursor MWW (P) has been developed to construd more active Ti species within the framework [24, 70], Figure 4.7 illustrates the strategy of this post-synthesis method of reversible strudural conversion. First, highly siliceous MWW is prepared from hydrothermally synthesized MWW boro-silicate by the combination of caldnation and acid treatment. Second, the MWW silicalite is treated with an aqueous solution of HM or PI and a Ti source. A reversible structure conversion from MWW into the corresponding lamellar precursor occurs as a result of Si-O-Si bond hydrolysis catalyzed by OH, which is supplied by basic amine molecules. This is accompanied by the intercalation of the amine molecules. 

Silica nanoparticles are commonly prepared by polymerization of appropriate precursors such as silicates, silicon alkoxides, or chlorides (Fig. 11.2).2 Besides the industrial methods, which rely mainly on condensation of sodium silicate in water induced by sodium removal through ion exchange, three different synthetic methods are currently used in research labs to prepare silica nanoparticles loaded with organic molecules. In the first method, proposed by Kolbe in 1956s and developed by Stober and coworkers in the late 1960s,6 the particles are formed via hydrolysis and... 

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