TY - JOUR
T1 - Kinetic and thermodynamic studies of silica nanoparticle dissolution
AU - Rimer, Jeffrey D.
AU - Trofymluk, Olga
AU - Navrotsky, Alexandra
AU - Lobo, Raul F.
AU - Vlachos, Dionisios G.
N1 - Funding Information:
Acknowledgement. This study was funded by a grant from the National Organization for Hearing Research. We wish to thank Kazim Husain for his assistance.
PY - 2007/8/21
Y1 - 2007/8/21
N2 - Small-angle X-ray scattering (SAXS) and microcalorimetry were used to study the dissolution of silica nanoparticles that serve as precursors in the synthesis of the pure-silica zeolite, silicalite-1. Temporal changes in nanoparticle size were monitored by SAXS to obtain radial dissolution rates on the order of 1 × 10-2 nm/min, 10 times greater than those of silicalite-1. Nanoparticle dissolution rates are independent of solution alkalinity (above pH 11) and particle surface area, although contributions from the latter account for more than 60% of the nanoparticle enthalpy of dissolution (13.5 ± 0.1 kJ/mol SiO2 relative to silicalite-1). We show that dissolution enthalpies and rates correlate to the molecular structure of silicates. Comparisons among amorphous silica, silicalite-1, and silica nanoparticles suggest that the latter are amorphous and therefore not simply small fragments of a crystalline zeolite. Nevertheless, they do possess a degree of ordering greater than that in dense amorphous silica. Dissolution experiments were also performed on heat-treated nanoparticles grown via Ostwald ripening. With increasing time of heat treatment, the nanoparticle dissolution rates and enthalpies decrease in magnitude toward those of silicalite1, suggesting a structural reorganization of silica within the particles. The results offer insight on silicalite-1 nucleation as well as relevant time scales and rate-determining steps involved in zeolite crystallization.
AB - Small-angle X-ray scattering (SAXS) and microcalorimetry were used to study the dissolution of silica nanoparticles that serve as precursors in the synthesis of the pure-silica zeolite, silicalite-1. Temporal changes in nanoparticle size were monitored by SAXS to obtain radial dissolution rates on the order of 1 × 10-2 nm/min, 10 times greater than those of silicalite-1. Nanoparticle dissolution rates are independent of solution alkalinity (above pH 11) and particle surface area, although contributions from the latter account for more than 60% of the nanoparticle enthalpy of dissolution (13.5 ± 0.1 kJ/mol SiO2 relative to silicalite-1). We show that dissolution enthalpies and rates correlate to the molecular structure of silicates. Comparisons among amorphous silica, silicalite-1, and silica nanoparticles suggest that the latter are amorphous and therefore not simply small fragments of a crystalline zeolite. Nevertheless, they do possess a degree of ordering greater than that in dense amorphous silica. Dissolution experiments were also performed on heat-treated nanoparticles grown via Ostwald ripening. With increasing time of heat treatment, the nanoparticle dissolution rates and enthalpies decrease in magnitude toward those of silicalite1, suggesting a structural reorganization of silica within the particles. The results offer insight on silicalite-1 nucleation as well as relevant time scales and rate-determining steps involved in zeolite crystallization.
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U2 - 10.1021/cm070708d
DO - 10.1021/cm070708d
M3 - Article
AN - SCOPUS:34548303251
SN - 0897-4756
VL - 19
SP - 4189
EP - 4197
JO - Chemistry of Materials
JF - Chemistry of Materials
IS - 17
ER -