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

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Title: Quantification of initial steps of nucleation and growth of silica nanoparticles: An in-situ SAXS and DLS study
Authors: Tobler, Dominique J.1 tobler@see.leeds.ac.uk, Shaw, Sam1, Benning, Liane G.1
Source: Geochimica et Cosmochimica Acta. Sep2009, Vol. 73 Issue 18, p5377-5393. 17p.
Subjects: Nucleation, Silica, Nanoparticles, Quantitative chemical analysis, Polymerization, pH effect, Chemical kinetics, Light scattering, Small-angle X-ray scattering
Abstract: 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 1600ppm ([SiO2]) and ionic strengths (IS) of 0.02, 0.05, 0.11 and 0.22M. 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 (1.4–2nm) and results from SAXS and DLS showed that over 3h the particle diameter increased to a final size of ∼8nm. 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. [Copyright &y& Elsevier]
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Abstract: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 1600ppm ([SiO2]) and ionic strengths (IS) of 0.02, 0.05, 0.11 and 0.22M. 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 (1.4–2nm) and results from SAXS and DLS showed that over 3h the particle diameter increased to a final size of ∼8nm. 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. [Copyright &y& Elsevier]
ISSN:00167037
DOI:10.1016/j.gca.2009.06.002