Langmuir, Vol.19, No.11, 4619-4626, 2003
Physicochemical characterization of silicalite-1 surface and its implications on crystal growth
The value of the silicalite-1 colloidal crystal surface zeta potential was estimated from electrophoretic mobility measurements. Potassium nitrate and tetrapropylammonium bromide have been used as background electrolytes, and the pH was varied between 2.4 and 11.6. Comparison with similar results obtained with colloidal silica particles supports the hypothesis that both potassium and tetrapropylammonium ions can adsorb in the exposed silicalite-1 pores. The results were further analyzed with the triple layer surface complexation model that captured the observed zeta potential trends. The adjustable parameters of the model have been optimized by using a combination of factorial design, solution mapping, and linear regression. Furthermore, the model was used to study the effect of composition on the apparent activation energy. It is demonstrated that when surface complexation model predictions are used as input in the silicalite-1 growth model, there is qualitative agreement between growth model results and experimental observations. This is the first time that a detailed mechanism can explain issues such as the effect of composition on apparent activation energy.