Aging effects on the nucleation and crystallization kinetics of colloidal TPA-silicalite-l

A direct experimental method, involving a two-stage varying-temperature synthesis, was utilized to investigate the effects of aging on the nucleation kinetics for the synthesis of nanosized TPA-silicalite-1 with various silica sources, including tetraethoxysilane (TEOS) and amorphous silica Ludox TM. For TEOS aging had only a mild influence on the nucleation and crystallization kinetics, whereas for Ludox TM dramatic changes occurred. After extended aging periods, the nucleation kinetics for syntheses with Ludox TM became similar to those for syntheses with TEOS, leading to increasing similarities in the properties of the products of the crystallization. Independent of aging time and silica source, the nucleation processes occurred over a substantial period of time, extending over the induction period, but were completed before crystal growth was detected. With increased aging, the nucleation period was gradually decreased and tended to be completed earlier in the induction period. Raman spectra revealed that with Ludox TM, aging enhanced the interaction between TPA(+) and the silica species, leading to an increase in the concentration of precursor species for nucleation, which in turn accelerated the nucleation rate. (C) 2001 Elsevier Science B.V. All rights reserved.