Study on template removal from silicalite-1 giant crystals

The formation of silicalite-1 giant crystals with a size of up to 3 mm can be achieved by controlling the factors affecting the nucleation and crystallization process using a piece of tube of quartz glass as the silica source under hydrothermal conditions. Once prepared and characterized by scanning electron and optical microscopy, thermogravimetry and single crystal powder X-ray diffraction, a challenge that remains is the removal of the template giving rise to colourless and crack-free crystals. As pointed out by stereoscopical, optical and fluorescence confocal optical microscopies, this was achieved in this study by the calcination protocols developed, involving the use of pure O2 and 5% of O2 in Ar and O2–O3 (1.5% of O3), maximum temperatures of 400 °C and heating rates as low as 0.5 °C/min.