Self-Assembly of Colloidal Zeolite Precursors into Extended Hierarchically Ordered Solids

A new porous material containing both micropores and mesopores has been synthesized by the self-assembly of silicalite-1 colloidal precursors at low temperatures and thoroughly investigated by diffraction, electron microscopy, porosimetry, and spectroscopy. Our “bottom-up” approach yields mesoporous materials that contain a microporosity different from that of SBA-15. For the samples where the silicalite-1 mixture is aged at room temperature, we do not have conclusive evidence that silicalite-1 is responsible for the microporosity in our samples, as all analytical techniques are inconclusive. By contrast, samples where the silicalite-1 mixture is heated until Bragg reflections are observed appear by TEM to be heterogeneous materials containing both mesopores and domains of silicalite-1. Nitrogen and argon adsorption show that both the micropore size distribution and the total micropore volume of our samples are different from those of SBA-15. The conclusions from this study are fourfold:  (1) we have created a material containing both micropores and mesopores that is very well ordered on the mesoscale, (2) our material has a larger micropore volume and different micropore size distribution than SBA-15 made under the same conditions, (3) we have achieved this high degree of structural ordering and uniformity without the need for high-temperature syntheses, and (4) it does not appear possible to use larger (∼50 nm) nanoparticles of silicalite-1 to fabricate homogeneous materials. The ability to synthesize these materials at low temperatures makes them (and the synthetic concept) ideal for extension into areas such as thin-film syntheses.