Combined NMR, SAXS, and DLS Study of Concentrated Clear Solutions Used in Silicalite-1 Zeolite Synthesis

Abstract

Concentrated clear solutions, as used for the preparation of Silicalite-1 zeolite, were synthesized from tetrapropylammonium hydroxide, tetraethylorthosilicate, and water. The solutions were analyzed using three techniques: quantitative 29 Si NMR, synchrotron small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS). 29 Si NMR showed the coexistence of silicate oligomers and particles. For the first time, both fractions were analyzed simultaneously, providing a global, quantitative description of the clear solution microstructure. The SAXS patterns, typical of interacting particles, could be used together with the 29 Si NMR deduced particle volume fraction to estimate a particle size. A careful analysis of DLS data of the dynamics of the suspensions revealed the occurrence of two diffusive processes. The faster process is a collective particle diffusion. The slower process corresponds to the particle selfdiffusion and is present because of the presence of polydispersity in size, shape, and/or surface charge. The self-diffusion coefficient provides a means to estimate the equivalent hydrodynamic radius. The observations hence reveal a complex, polydisperse mixture of particles present at the onset of the Silicalite-1 zeolite formation. Implications on the proposed zeolite formation mechanisms are briefly discussed.

Investigation of the Mechanism of Colloidal Silicalite‐1 Crystallization by Using DLS, SAXS, and 29Si NMR Spectroscopy

“…Scattering techniques carried out in situ, such as dynamic light scattering (DLS) and synchrotron small-angle X-ray scattering (SAXS), have been successfully applied to determine the particle dimensions and shapes. [5][6][7][8] The silicon speciation is accessible through liquid-state 29 Si NMR spectroscopy. [5,6,9] Cryo-TEM analysis of frozen clear sols and TEM analysis of dried sols revealed the presence of a zeolite lattice in small particles collected early in the crysAbstract: Colloidal silicalite-1 zeolite was crystallized from a concentrated clear sol prepared from tetraethylorthosilicate (TEOS) and aqueous tetrapropylammonium hydroxide (TPAOH) solution at 95 8C.…”

“…[5][6][7][8] The silicon speciation is accessible through liquid-state 29 Si NMR spectroscopy. [5,6,9] Cryo-TEM analysis of frozen clear sols and TEM analysis of dried sols revealed the presence of a zeolite lattice in small particles collected early in the crysAbstract: Colloidal silicalite-1 zeolite was crystallized from a concentrated clear sol prepared from tetraethylorthosilicate (TEOS) and aqueous tetrapropylammonium hydroxide (TPAOH) solution at 95 8C. The silicate speciation was monitored by using dynamic light scattering (DLS), synchrotron smallangle X-ray scattering (SAXS), and quantitative liquid-state 29 Si NMR spectroscopy.…”

“…[5,6,9] Herein, we extend the investigation over the entire crystallization process and combine 29 Si NMR spectroscopy with DLS and synchrotron SAXS to seek answers to the standing questions. Gaining insight into the structuring of nanoparticles involved in zeolite crystallization not only is of fundamental importance, but also has immediate practical impact.…”

Evidence of Large Voids in Pure‐Silica‐Zeolite Low‐k Dielectrics Synthesized by Spin‐on of Nanoparticle Suspensions

“…In the period from 3 to 5 days the Silicalite-1 nanocrystal content increased by growth of existing nanocrystals and formation of additional ones. [33,34] To simulate the spin on Silicalite-1 film as previously done in literature, [8][9][10] samples of Silicalite-1 suspensions were dried and calcinated. Nitrogen and argon adsorption isotherms were determined at À196 8C on this powdery Silicalite-1 (Fig.…”

Aggregation and crystallisation in space

“…Very early in clear solution formation 2-4 nm sized particles appear, which are thought to be precursors for the final zeolite structure [1,2]. They consist of a silica core enclosed by a template shell [3]. Over time silica-template interplay leads to successive structure optimization within these precursors.…”