Microwave Molecular Sieves Synthesis and Capillary Crystal Growth by Geometric Confinement.
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A5.13.1
Microwave Molecular Sieves Synthesis and Capillary Crystal Growth by Geometric Confinement. 1
Steven B. Ogunwumi, John F. Wight2, James C. Fajardo3 Crystalline Materials Research1, Inorganic Processing2, Surfaces and Interfaces3 Corning Incorporated, Painted Post, NY, USA 14870
ABSTRACT Microwave heating is an alternate means for material processing. The technique is promising for the accelerated synthesis of new materials. Microwave molecular sieves synthesis is combined with capillary confinement as a novel synthetic method. It is successfully demonstrated in the preparation of small ZSM-5 crystals by microwave hydrothermal synthesis within 1-1.7 µm channels of a capillary bundle. The geometric and spatial confinement offered by the capillary is expected to define and control the resulting crystal size distribution and orientation. MCM-41, a mesoporous molecular sieve with a uni-dimensional regular array of hexagonal channels is investigated as a candidate for capillary confinement. The large porous channels of MCM-41(>35 Å ) is attractive as a host for promoting inclusions of guest molecules or templates. The successful confinement of MCM-41 represents an important step towards the alignment of molecular sieves in a defined orientation within thin capillaries bundled (less than 5 µm channels). Ultimately, such an approach may be useful for the fabrication of new molecular sieve devices. INTRODUCTION Crystals of ZSM-5 were successfully grown within the channels of a 1-1.7 and 34 µm bundled capillary fiber using microwave hydrothermal synthesis. Microwave heating has been previously shown to reduce the synthesis time of ZSM-5 to hours in comparison to conventional hydrothermal synthesis, usually requiring several days [1]. In this document, the results of small sized molecular sieves crystal grown by capillary confinement are presented. Occlusion of zeolite pores with functional materials, resulting in a sensor or optical device has been reported [2]. MCM-41 and AlPO4-5 molecular sieves have unidimensional pore systems that are suitable and unique for alignment within (1-1.7 or 3-4 µm diameter) capillary channels. The large pore structures of these uni- dimensional molecular sieves may serve as host for guest molecules with specific functionality and desired properties. The orientation and alignment of guest molecules within the pores of these molecular sieves may result in new and interesting materials with enhanced properties. This may be potentially useful for new developments in the areas of catalysis, sensors, separation, and optical-electronic applications.
A5.13.2
EXPERIMENTAL SECTION Capillary bundle fibre Hollow core fibers were used as capillaries for the experiments conducted in this section [3]. These capillaries are made from silica. The diameter of the entire bundled fiber is typically 125 µm. The individual channels diameter may vary slightly. Two kinds of bundled fiber were used in these experiments. The smaller fiber consisted of channels between the range of 1-1.7 µm in diameter and
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