Initial stages of self-organization of silica-alumina gels in zeolite synthesis.

We report the effect of aluminum on the formation and structure of silica nanoparticles formed in basic solutions of small organic and inorganic cations using a combination of small-angle X-ray scattering, conductivity, pH, and 27Al NMR spectroscopy methods. At low silica concentrations, our observations agree with previous reports and show the formation of small oligomers ((HO)4-nAl(OSi(OH)3)n)- that can be modeled qualitatively using a simple aqueous speciation model. We also find that aluminum drastically reduces the concentration of silica at which nanoparticles are formed.

Silica self-assembly and synthesis of microporous and mesoporous silicates.

The microstructure of silica in basic aqueous solutions containing organic cations and prepared from monomeric precursors is reviewed and interpreted within the context of classical ideas of self-assembly of molecular aggregates. The solution properties can be understood by using the pseudo-phase separation approach coupled to the acid-base chemistry of silanol groups and the Poisson-Boltzmann equation. The silica nanoparticles frequently observed in these systems have a core-shell structure with silica in the core and the organic cations at the shell.

Formation and structure of self-assembled silica nanoparticles in basic solutions of organic and inorganic cations.

The phase behavior of silica solutions containing organic and inorganic cations was studied at room temperature using conductivity, pH, and small-angle scattering experiments. A critical aggregation concentration (cac) was observed at approximately 1:1 ratio of SiO(2)/OH(-) for all cation solutions from conductivity and pH studies. From this cac, a phase diagram of the system was developed with three distinct phase regions in pseudoequilibrium: a monomer/oligomer region (I), a monomer/oligomer/nanoparticle region (II), and a gel region (III).