title: Mechanistic principles of nanoparticle evolution to zeolite crystals.
abstract: 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.
authors.affiliation: University of Minnesota, Department of Chemical Engineering and Materials Science, 151 Amundson Hall, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, USA.
authors.forename: Tracy M
authors.initials: TM
authors.lastname: Davis
authors.forename: Timothy O
authors.initials: TO
authors.lastname: Drews
authors.forename: Harikrishnan
authors.initials: H
authors.lastname: Ramanan
authors.forename: Chuan
authors.initials: C
authors.lastname: He
authors.forename: Jingshan
authors.initials: J
authors.lastname: Dong
authors.forename: Heimo
authors.initials: H
authors.lastname: Schnablegger
authors.forename: Markos A
authors.initials: MA
authors.lastname: Katsoulakis
authors.forename: Efrosini
authors.initials: E
authors.lastname: Kokkoli
authors.forename: Alon V
authors.initials: AV
authors.lastname: McCormick
authors.forename: R Lee
authors.initials: RL
authors.lastname: Penn
authors.forename: Michael
authors.initials: M
authors.lastname: Tsapatsis