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Issue 36, 2008
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Characterization of nanoparticles in diluted clear solutions for Silicalite-1 zeolite synthesis using liquid 29Si NMR, SAXS and DLS

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Abstract

Clear solutions for colloidal Silicalite-1 synthesis were prepared by reacting tetraethylorthosilicate in aqueous tetrapropylammonium hydroxide solution. A dilution series with water resulting in clear solutions with a TEOS ∶ TPAOH ∶ H2O molar ratio of 25 ∶ 9 ∶ 152 up to 25 ∶ 9 ∶ 15 000 was analysed using liquid 29Si nuclear magnetic resonance (NMR), synchrotron small angle X-ray scattering (SAXS) and dynamic light scattering (DLS). Particle sizes were derived independently from DLS and from the combination of SAXS and NMR. NMR allowed quantitative characterization of silicon distributed over nanoparticles and dissolved oligomeric silicate polyanions. In all samples studied, the majority of silicon (78–90%) was incorporated in the nanoparticle fraction. In concentrated suspensions, silicate oligomers were mostly double-ring species (D3R, D4R, D5R, D6R). Dilution with water caused their depolymerisation. Contrarily, the internal condensation and size of nanoparticles increased with increasing dilution. SAXS revealed a decrease of effective nanoparticle surface charge upon dilution, reducing the effective particle interactions. With DLS, the reduction of nanoparticle interactions could be confirmed monitoring the collective diffusion mode. The observed evolution of nanoparticle characteristics provides insight in the acceleration of the Silicalite-1 crystallization upon dilution, in view of different crystallization models proposed in the literature.

Graphical abstract: Characterization of nanoparticles in diluted clear solutions for Silicalite-1 zeolite synthesis using liquid 29Si NMR, SAXS and DLS

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Article information


Submitted
02 Apr 2008
Accepted
11 Jun 2008
First published
23 Jul 2008

Phys. Chem. Chem. Phys., 2008,10, 5574-5583
Article type
Paper

Characterization of nanoparticles in diluted clear solutions for Silicalite-1 zeolite synthesis using liquid 29Si NMR, SAXS and DLS

L. R. A. Follens, A. Aerts, M. Haouas, T. P. Caremans, B. Loppinet, B. Goderis, J. Vermant, F. Taulelle, J. A. Martens and C. E. A. Kirschhock, Phys. Chem. Chem. Phys., 2008, 10, 5574
DOI: 10.1039/B805520C

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