Journal
LANGMUIR
Volume 23, Issue 5, Pages 2784-2791Publisher
AMER CHEMICAL SOC
DOI: 10.1021/la062828q
Keywords
-
Ask authors/readers for more resources
We show that germania nanoparticle self-assembly in basic aqueous solutions occurs at a critical aggregation concentration (CAC) corresponding to a 1:1 GeO2/OH- molar ratio. A combination of pH, conductivity, and small-angle X-ray scattering (SAXS) measurements was used to monitor the effect of incremental additions of germanium (IV) ethoxide to basic solutions of sodium hydroxide or tetraalkylammonium cations. Plots of pH versus total germania concentration at varying alkalinities generated a phase diagram with three distinct regions. The diagram was analyzed with a thermodynamic model based on the chemical equilibria of germania speciation and dissociation. The model, which uses the GeO-H dissociation constant (pK = 7.1) as the single fitting parameter, quantitatively captures trends in the CAC and pH. SAXS patterns reveal that the germania nanoparticles have either a cubic or a spherical geometry of dimension similar to 1 nm that is independent of solution pH and cation. On the basis of these and other literature findings, we propose that the germania nanoparticle structure is that of the cubic octamer (double four-membered ring, Ge8O12(OH)(8)), which is common among condensed GeO2 materials and building units in [Ge,Si]-zeolites. Comparisons between germania and silica solutions show distinct differences in their phase behavior and nanoparticle structure. The results presented here, in combination with previous studies of siliceous solutions, provide a framework for ongoing studies of combined germania-silica phase behavior, which is part of an overarching effort to understand the influence of heteroatoms in the growth and structure direction of zeolites.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available