Hollow silica nanopartides

Scheme 8 Formation of cross-linked hollow spheres by (a) silica nanopartide templated layer-by-layer (LbL) assembly of polyelectrolytes, (b) cross-linking of polymer multilayer assembly by TEC, (c) functionalization with PEG using residual thiol, and (d) removal of silica core by hydrofluoric acid (HF) etch. ...

Increasing the methylation levels in the C3N3 species also increased the third-order rate constant For aU of the kineticaUy active species, the silica nanopartides produced were nonporous, which is most likely due to rapid nucleation. Thus, by modifying the composition of the polyamine, the abiUty to produce microemulsions which lead to hollow silica and the porosity of the silica can be tailored, leading to the production of a variety of potential nanomaterials [77]. 

Caruso, R.A., Susha, A. and Caruso, F. (2001) Multilayered titania, silica, and laponite nanopartides coating on polystyrene colloidal templates and resulting inorganic hollow spheres. Chemistry of Materials, 13, 400—409. 

Hollow siUca nanoparticles can be synthesized under moderate conditions using luminescent CdSe/ZnS nanoparticles, as described by Darbandi et al. [9]. The synthesis is conducted at room temperature within reverse micelles and by way of a modified water-in-oil microemulsion system, where silica is formed from the hydrolysis of TEOS. Here, the silica acts as a host for the CdSe/ZnS nanoparticles while the latter is simultaneously dissolved. The extent of this dissolution is determined by the amount of ammonia aqueous solution used and the reaction time. In a typical synthesis, cyclohexane is added to polyethylene glycol nonylphenyl ether (the surfactant), pre-prepared luminescent CdSe/ZnS nanopartides in chloroform, and TEOS, and the mixture then stirred vigorously to form the microemulsion. After 30 min, aqueous ammonia is added to initiate the encapsulation, and the reaction is then left overnight at room temperature before the nanopartides are precipitated. By increasing the amount of ammonia used, the core particles become increasingly dissolved to the point where hollow spheres can be obtained (250 (xl ammonia solution). Similarly, an increase in the duration of the reaction will yield nanopartides with increasingly dissolved cores. 

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