THE SYNTHESIS OF DISCRETE COLLOIDAL PARTICLES OF TPA-SILICALITE-1

Discrete colloidal particles of TPA-silicalite-l with an average parti cle size of less than 100 nm and with a narrow particle-size distribut ion have been synthesized in clear homogeneous solutions. The factors influencing particle size have been investigated. High silica contents in conjunction with high alkalinities favor the synthesis of colloida l silicalite suspensions. Polymeric silica sources result in larger pa rticles compared to those synthesized with tetraethoxy silane-presumab ly due to the different nucleation kinetics. It was found that the bas e concentration influences nucleation behavior in that high alkaliniti es result in the nucleation of a relatively large number of particles. The growth rates are constant for a given silica content irrespective of the alkalinity, at least within the alkalinity range studied. This result is ascribed to a rate-limiting surface reaction step that is a consequence of the synthesis mixture composition. The linear growth r ates recorded are lower than those typically reported in the literatur e.