Potassium cation induced controllable synthesis of CAN zeolite hollow microspheres

• Hollow zeolite spheres were synthesized by one-step organic-free hydrothermal method from natural minerals.
• The diameters of the microsphere were controlled with potassium cation concentration.
• A possible K-induced Ostwald ripening reversed crystal growth process was proposed.

A novelty hierarchical hollow nitrate cancrinite zeolite microspheres (HNCMs) with micro-plate crystals act as sphere shell and wrapped with large number of nanorods crystal in the center of the microspheres were synthesized by a simple organic-free hydrothermal synthesis methods. With the adjustment of potassium cation concentration in synthetic system, nitrate cancrinite zeolites realize morphology tunable architectures from nanorod to HNCMs. A systematic investigation of the crystal growth over different crystallization stages indicates a stepwise crystallization progress of HNCMs. First, the primitive nitrate cancrinite nanoplatelets self assembled to yield solid spherical clusters. Then the spherical clusters undergo a surface to core crystallization progress which was supposed to be the reason for the formation of hollow cores. This work provides an alternative strategy for the synthesis of spherical hollow zeolite materials with tunable architectures, which may potentially be used in the field of separation, catalysis and biomedicine.

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