Nanoparticle formation and zeolite growth in TEOS/Organocation/water solutions

This work investigates nanoparticle formation and zeolite growth in several tetraethyl orthosilicate (TEOS)/organocation/water solutions heated at 368 K using small-angle X-ray scattering. The effect of several synthesis parameters including organocation identity, hydroxide content, alkali content, synthesis temperature, ethanol content, and seeding are investigated. In all cases the TEOS/organocation/water solutions lead to colloidal silica nanoparticles both after aging at room temperature and after hydrothermal treatment. In addition, the size, number density, and shape of the colloidal particles depend on the organocation identity. However, in contrast to TEOS/TPAOH/water mixtures that rapidly form silicalite-1 at 368 K, none of the investigated solutions can direct the formation of a zeolite phase at 368 K. The key point that emerges from this investigation is that it is not straightforward to synthesize siliceous zeolites from clear solutions at 368 K with the investigated organocations under the conditions where silicalite-1 forms in a matter of hours. These results suggest that the zeolite community may wish to take pause before formulating a "general" description of zeolite nucleation and growth from the studies of silicalite-1 grown from clear solution at 368 K.