By YU Jihong's Group

Aluminosilicate zeolites have been widely used as ion-exchangers, catalysts, and adsorbents. Since the first synthesis of zeolite materials in the 1940s, the crystallization mechanism of such materials has attracted great interest, but remains unclear until now. The mechanisms proposed so far are generally based on the knowledge that the crystallization process of is catalyzed by hydroxide ions. Hydroxide ions (OH-) catalyze the de-polymerization of the aluminosilicate gel by breaking the T-O-T (T=Si, Al) bonds and the polymerization of the aluminosilicate anions around the hydrated cation species, by remaking the T-O-T bonds.   Prof. Yu and her coworkers discover for the first time that hydroxyl free radicals (•OH) are also involved in the zeolite crystallization, which has not been aware before. This finding will significantly advance the scientific understanding on the crystallization mechanism of zeolites, and open new perspectives for zeolite synthesis. The theoretical calculations further provide valuable insights into the understanding of the role of hydroxyl free radicals in ccelerating the zeolite crystallization.

The discovery that zeolite synthesis mechanism can be promoted through free radicals sheds a new light on zeolite crystallization, and will open new perspectives for the synthesis of zeolite materials that are largely demanded in chemical industry. The respective work was published in Science in March 2016 (Science, 2016. 351, 1188-1191).

•OH radicals accelerate zeolite crystallization

Reaction of [SiO₂(OH)-O-SiO₃]Na₅ system and Gibbs free energy calculation. Reaction of [SiO₂(OH)-O-SiO₃]Na₅ system with OH^- and with •OH. Calculated Gibbs free energy profiles for the reaction of [SiO₂(OH)-O-SiO₃]Na₅ model with OH^- (blue) and with •OH (red).