Mechanistic principles of nanoparticle evolution to zeolite crystals.
Precursor nanoparticles that form spontaneously on hydrolysis of tetraethylorthosilicate in aqueous solutions of tetrapropylammonium (TPA) hydroxide evolve to TPA-silicalite-1, a molecular-sieve crystal that serves as a model for the self-assembly of porous inorganic materials in the presence of organic structure-directing agents. The structure and role of these nanoparticles are of practical significance for the fabrication of hierarchically ordered porous materials and molecular-sieve films, but still remain elusive. Here we show experimental findings of nanoparticle and crystal evolution during room-temperature ageing of the aqueous suspensions that suggest growth by aggregation of nanoparticles. A kinetic mechanism suggests that the precursor nanoparticle population is distributed, and that the 5-nm building units contributing most to aggregation only exist as an intermediate small fraction. The proposed oriented-aggregation mechanism should lead to strategies for isolating or enhancing the concentration of crystal-like nanoparticles.
Davis
Tracy M
TM
University of Minnesota, Department of Chemical Engineering and Materials Science, 151 Amundson Hall, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, USA.
Drews
Timothy O
TO
Ramanan
Harikrishnan
H
He
Chuan
C
Dong
Jingshan
J
Schnablegger
Heimo
H
Katsoulakis
Markos A
MA
Kokkoli
Efrosini
E
McCormick
Alon V
AV
Penn
R Lee
RL
Tsapatsis
Michael
M