A systematic investigation of silicalite-1 precursor mixtures with varying degrees of dilution

The effect of the composition on conductivity, pH, and particle size distribution (PSD) in precursor mixtures of silicalite-1 was studied in this work. Mixtures of TPAOH, TEOS, and water spanning a broad composition range were analyzed. Conductivity and pH measurements reported are consistent with previous investigations about the conductivity and pH behavior above and below the critical aggregation concentration (CAC). Dynamic light scattering (DLS) measurements were performed to determine the PSD. ‘Dilute’ mixtures (H2O/TEOS >65) showed trimodal PSDs with nanoparticles of ∼11 nm in diameter, small aggregates of ∼340 nm in diameter, and aggregates larger than 1 μm. The distribution of nanoparticles and aggregates changed with the mixture composition as the intensity-weighted PSDs showed more aggregates in mixtures with higher water content. However, a comparison between intensity-, volume-, and number-weighted PSDs showed that the amount of aggregates present is smaller than the amount of nanoparticles. It was also observed that TPAOH concentration slightly affected the nanoparticle size, which decreased at high TPAOH concentration. On the other hand, concentrated mixtures did not show a clear dependence of PSD or nanoparticle size on the mixture composition. Interestingly, and in contrast with ‘dilute’ mixtures that only showed one population of nanoparticles, two populations of nanoparticles of ∼2 nm and ∼30 nm were observed in the concentrated mixtures. The information presented in this work attempts to provide a better understanding of silicalite-1 precursors and shows the effect of the composition on the phase behavior of these synthesis mixtures. Thus, this work should help to unify previous findings on nucleation and growth among silicalite-1 mixtures with different compositions.

Silicalite-1 precursors solutions spanning a wide range of composition space are reported..Figure optionsDownload as PowerPoint slideHighlights
► An exhaustive investigation of silicalite-1 precursor solutions is reported.
► The effect of dilution on pH, conductivity, and particle size is shown.
► This work provides a self-consistent set of data for the zeolite science community.