Quantitative correlation between morphology of silicalite-1 crystals and dielectric constants of solvents

The quantitative correlation between morphology of silicalite-1 (Si-MFI) crystals and dielectric constants of solvents for the reaction system of TEOS–TPAOH-alcohol under microwave heating was investigated. The dielectric constant of the solvent was finely tuned by mixing water and additional alcohols according to the equation of εm=Φ1ε1+Φ2ε2+⋯+Φnεnεm=Φ1ε1+Φ2ε2+⋯+Φnεn. The length and fraction of Si-MFI crystals with self-stacked morphology as a function of dielectric constant was investigated, and the linear correlation was found. The self-stacked crystals were obtained when the dielectric constant of the mixed solvent was lower than 41.0, while only fully isolated crystals were formed when the dielectric constant was higher than 45.0. The regularities observed in the microwave-assisted solvothermal synthesis system were not observed in the conventional oven-heated solvothermal synthesis system.