Quantification of initial steps of nucleation and growth of silica nanoparticles: an in-situ SAXS and DLS study

Tobler, D.J., Shaw, S. and Benning, L.G. (2009) Quantification of initial steps of nucleation and growth of silica nanoparticles: an in-situ SAXS and DLS study. Geochimica et Cosmochimica Acta, 73(18), pp. 5377-5393. (doi: 10.1016/j.gca.2009.06.002)

Abstract

The initial steps of silica polymerization and silica nanoparticle formation have been studied in-situ and in real-time. The experiments were carried out in near neutral pH (7–8) solutions with initial silica concentrations of 640 and 1600 ppm ([SiO₂]) and ionic strengths (IS) of 0.02, 0.05, 0.11 and 0.22 M. The polymerization reactions were induced by neutralizing a high pH silica solution (from pH 12 to 7) and monitored by the time-dependent depletion in monosilicic acid concentration over time. The accompanied nucleation and growth of silica nanoparticles (i.e., change in particle size over time) was followed in-situ using time-resolved synchrotron-based Small Angle X-ray Scattering (SAXS) and conventional Dynamic Light Scattering (DLS) combined with scanning and (cryo)-transmission electron microscopy (SEM/cryo-TEM). The critical nucleus diameter was quantified (1.4–2 nm) and results from SAXS and DLS showed that over 3 h the particle diameter increased to a final size of ∼8 nm. SEM and TEM photomicrographs verified the SAXS and DLS data and confirmed the spherical and hydrous structure of the forming silica nanoparticles. Furthermore, fractal analysis (i.e., fractal dimension, D_m ∼2.2) indicated that the formed particles consisted of open, polymeric, low-density structures. For the nucleation and growth of silica nanoparticles a 3-stage growth process is proposed: (1) homogeneous and instantaneous nucleation of silica nanoparticles, (2) 3-D, surface-controlled particle growth following 1st order reaction kinetics and (3) Ostwald ripening and particle aggregation.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Tobler, Dr Dominique
• Authors: Tobler, D.J., Shaw, S., and Benning, L.G.
• Subjects: Q Science > QE Geology
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences
• Journal Name: Geochimica et Cosmochimica Acta
• Journal Abbr.: Geochim. cosmochim. acta.
• ISSN: 0016-7037
• ISSN (Online): 1872-9533
• Published Online: 14 June 2009