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The syntheses of zeolites involve very complex nucleation and growth processes. During the past decade, significant progress has been made towards understanding zeolite crystallization mechanisms. This progress has been made possible by advanced analytical techniques, such as high-resolution transmission electron microscopy (HRTEM), small-angle X-ray scattering, and atomic force microscopy. [1][2][3][4][5] A number of zeolite growth mechanisms were proposed based on the respective synthesis of the zeolites. For instance, by monitoring the crystallization of silicalite-1 from silica sols in tetrapropylammonium ion (TPA) at room temperature, an oriented aggregation mechanism was proposed.[4] In the growth mechanism of zeolite A evolving from the nuclei inside the amorphous gel, the particles gradually grow into larger crystals by consuming the surrounding amorphous gels.[2] The gel was formed by using aluminosilicate solutions and tetramethylammonium hydroxide as the structure-directing agent (SDA).[2] For zeolite A formation, evidences of nucleation at the solid-liquid interface of the gel cavities were also found in sodium aluminosilicate gels without organic SDA.[3] In addition, a reversed crystal growth process from the surface to the core of nanocrystallite aggregates was observed in the crystal growth of zeolite analcime icositetrahedra.[6] These studies have undoubtedly provided new insights into zeolite crystallization processes.As non-structure-directing agents, organic polymers have significant effects on zeolite nucleation and growth. The confinement of sodium aluminosilicate zeolite gels in thermoreversible methylcellulose hydrogels resulted in zeolite A and X nanocrystals under hydrothermal treatment.[7] Crosslinked polyacrylamide hydrogels was used to reduce SAPO-34 crystal sizes in vapor-phase transport synthesis. [8] In all these cases, the small crystal sizes is due to space confinement of the polymer hydrogel networks. Hollow sodalite spheres and zeolite A crystals were also synthesized hydrothermally in the presence of crosslinked polyacrylamide hydrogels. It was suggested that the scaffolds of polyacrylamide hydrogels were the preferential sites for zeolite nucleation, and promoted the direction of nanoparticle aggregation subsequent to the surface-to-core growth.[9] These results suggest that the roles of polymer hydrogels in zeolite synthesis are complex, and syntheses of the zeolites depend on the microstructure of the polymer hydrogels and the interaction between the polymer chains and the zeolite gels.Herein we report the formation of cubes of zeolite A with a single crystalline shell and an amorphous core by in-situ crystallization of sodium aluminosilicate gel inside the polymer networks of uncrosslinked chitosan hydrogel. This work provides further direct evidence for the surface-to-core reversed-growth mechanism. Chitosan is a biopolymer derived from chitin that is found in a wide range of natural sources, such as crab, lobster, and shrimp shells. Chitosan, containing abundant amino and...

Macroporous NaP zeolite monoliths (M-ZPMs) with designed shapes such as cylinder, rectangularprism, and donut shapes were synthesized via gelcasting of the aged zeolite gel with colloidal silica as a binder and subsequent vapor-phase-transport (VPT) synthesis. X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury porosimetry, and nitrogen gas adsorption were used to characterize the samples at different synthesis stages. SEM images revealed that the resulting macroporous NaP zeolite monoliths were composed of interconnected hollow particles. Mercury porosimetry showed that the macroporous NaP zeolite monoliths possessed bimodal macropore size distributions involving the textural macropores (ca. 100 μm) and skeletal macropores (ca. 3.5 μm). Furthermore, colloidal silica played a crucial role in the formation of robust macroporous NaP zeolite monoliths. Specifically, as the mass loading of colloidal silica in the zeolite-gel monoliths increases, the mechanical strength and Si/Al ratio of the resulting zeolitic monoliths increased; dispersible and individual hollow NaP zeolite particles with lower Si/Al ratios were produced in the absence of colloidal silica. The formation mechanisms of the hollow NaP zeolites in the VPT synthesis process were discussed. The incorporation of functional magnetic Fe 3 O 4 in M-ZPMs was finally presented.