Colloidal Defect-Free Silicalite-1 Single Crystals: Preparation, Structure Characterization, Adsorption, and...

In this work, colloidal silicalite-1 single crystals are for the first time synthesized using fluoride as mineralizing agent at near neutral pH. SEM, TEM, DLS, XRD, solid-state (29)Si MAS NMR, and adsorption/desorption experiments using nitrogen, water, n-butanol, and ethanol as adsorbates were used to characterize the crystals. The single crystals have a platelike habit with a length of less than 170 nm and an aspect ratio (length/width) of about 1.2, and the thickness of the crystals is less than 40 nm. Compared with silicalite-1 crystals grown using hydroxide as mineralizing agent, the amount of structural defects in the lattice is significantly reduced and the hydrophobicity is increased. Membrane separation and adsorption results show that the synthesized defect-free crystals present high selectivity to alcohols from alcohol/water mixtures. The n-butanol/water adsorption selectivities were ca. 165 and 14 for the defect-free crystals and a reference sample containing defects, respectively, illustrating the improvement in n-butanol/water selectivity by eliminating the polar silanol defects.