Template-free synthesis of zeolite nanocrystalline with controllable phase and composition

This study reports a template-free hydrothermal synthesis of zeolite nanocrystals with controllable phase and composition. The controlled formation of sodalite (SOD) nanocrystals was primarily achieved through temperature modulation. Phase transitions in zeolite nanocrystals exhibited significant temperature dependence, sequentially yielding zeolite a, hydroxy-SOD, and cancrinite (CAN) as hydrothermal temperatures increased from 50 °C to 160 °C. Notably, hydroxy-SOD with consistent polyhedral morphology was obtained across a broad temperature range (60 °C-150 °C). Furthermore, a two-step synthesis strategy enabled the construction of hydroxy-SOD-CAN heterojunctions with tunable phase ratios in mixed crystals, demonstrating 38% higher CAN yield compared to single-step process. The crystallization mechanisms involve temperature-dependent assembly of [AlO4] and [SiO4] structural units, with phase transformation from hydroxy-SOD to CAN initiating at surface active sites. The hydroxy-SOD nanocrystals exhibit excellent nitrogen adsorption capacity, reaching up to 266 cm³g^-1.