Understanding the effect of specific surface area and surface reactions on silicalite-1 nucleation and growth

During silicalite-1 nucleation and growth from clear solutions the nanoparticle specific surface area, defined as the ratio of external surface of the nanoparticles to the nanoparticle mass, decreases more than two orders of magnitude. The effect of such changes in solution properties such as pH, TPA+ activity and nanoparticle ζ-potential have been investigated using surface complexation modeling. The observed changes are explained by using the reactions taking place on the surface of silicalite-1 nanocrystals, namely the deprotonation of the surface silanol groups, the TPA+ specific adsorption on surface silanol sites, and the TPA+ adsorption on the pore openings exposed on the silicalite-1 surface. Simulations showed that both pH and TPA+ activity are expected to increase during nucleation and growth. The rise in pH is attributed to the decrease of the surface silanol concentration, while the increase of TPA+ activity can be attributed to the release of TPA+ cations adsorbed on the silicalite-1 pores exposed to the surface. The effect of composition on the magnitude of such changes is also discussed and compared with experimental results. Finally, the effect of composition on silicalite-1 nucleation and growth is discussed based on the calculated values of ζ-potential.