Verena Goertz, Alexander Gutsche, Nico Dingenouts, Hermann Nirschl

J. Phys. Chem. C 2012, 116, 26938−26946

Abstract:

The present publication focuses on the specific synthesis of SiO₂ multiplets by the sol−gel process according to Stöber. The experiments were analyzed by means of smallangle X-ray scattering and TEM. To evaluate the experimental scattering data of various aggregate structures (multiplets), simulations had to be performed first in order to study theinfluence of the multiplet structures on the scattering data. It was shown that the nonisometry ratio Q_NI proposed by us, the quotient of two different gyration radii R_g,Guinier/R_g,qmax1, allows for a very simple and rapid evaluation of the multiplet structure. For the production of multiplet structures, ammonia concentration was varied while keeping the other process parameters constant. At low catalyst concentrations, the aggregate structures desired were synthesized due to low stabilization of primary particles. With increasing ammonia concentration, single, nonaggregated particles were obtained. A defined primary particle size was achieved by an adaptation of the precursor concentration and the reaction temperature. The multiplet structures were evaluated by determining the ratio Q_NI from the experimental scattering data. In order to evaluate the primary particle size distributions, the curves of the aggregate structures were fitted using previously performed simulations. The results obtained from the scattering data were in good agreement with the TEM images.