title: Role of subcolloidal (nanosized) precursor species in the early stage of the crystallization of zeolites in heterogeneous systems.
abstract: A critical analysis was carried out for the purpose of understanding the role of subcolloidal (nanosized) (alumino)silicate precursor species in the early stage of crystallization of zeolites in heterogeneous systems (hydrogels). The formation and evolution of these subcolloidal species in both the solid and the liquid phases were investigated by various experimental methods such a scanning electron microscopy (SEM, FE-SEM), transmission electron microscopy, atomic force microscopy, particle size analysis, pH measurement, atomic absorption spectroscopy, and dynamic light scattering, after careful separation of intermediates from reaction mixture by two-step centrifugation treatment. The results revealed that a chain of processes (i) the formation of low-molecular-weight (LMW) silicate species, by dissolution of Al-enriched amorphous silica, and their aggregation into about 3 nm sized primary precursor species (PPSs), (ii) the formation of larger (∼3 to ∼15 nm sized) silicate precursor species (LSPSs) by a rapid aggregation/coalescence of PPSs, (iii) the formation of "gel" (primary amorphous precursor) by a random aggregation of LSPSs at room temperature, and (iv) the formation of the worm-like particles (secondary amorphous precursor) occurred in the solid phase during heating of the reaction mixture (hydrogel) from room temperature to 170 °C. It is interesting that almost the same processes occur in the liquid phase but with decreased rate according to the relative low concentration of LMW silicate species. With the above described findings, it is highly expected that the manipulation of crystallization pathway through controlling the formation/evolution of precursor species in the initial stage of the process can be achieved.
authors: Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Institute of Catalysis, and Laboratory of Advanced Material, Fudan University , 220 Han Dan Road, Shanghai 200433, P.R. China.
authors: Nan
authors: N
authors: Ren
authors: Sanja
authors: S
authors: Bosnar
authors: Josip
authors: J
authors: Bronić
authors: Maja
authors: M
authors: Dutour Sikirić
authors: Tea
authors: T
authors: Mišić
authors: Vesna
authors: V
authors: Svetličić
authors: Jian-Jiang
authors: JJ
authors: Mao
authors: Tatjana
authors: T
authors: Antonić Jelić
authors: Mirko
authors: M
authors: Hadžija
authors: Boris
authors: B
authors: Subotić
mesh_terms: D003460:Crystallization; D008855:Microscopy, Electron, Scanning; D017640:Silicates / Q000737:chemistry; D017641:Zeolites / Q000737:chemistry*
chemical_list: D017640:Silicates; D017641:Zeolites